Just my luck...so, what's the bad news???

[NoSpeedLimits]

I am picking my car up this evening after the shop is done putting the finishing touches on my new paint job. Yippy!!! Obviously, I am going to want to show her off. Hence, my dilemma... Prior to dropping her off I learned that my A/C was not working properly - only blowing hot air. And since it 90 degrees outside, I need help. I had asked some questions on this forum last month, http://www.bimmer.info/forum/showthread.php?p=28297&highlight=a%2Fcand and based on the responses the first thing I decided to do was have the A/C system recharged. Consequently, I found out that my auxiliary fan was not working. So, I bought the replacement ballast resistor for the aux. fan and picked up a new aux. fan switch socket (figured I'd replace it while I was doing A/C maintenance). I have plans to replace them this weekend. Anyway, the mechanic that did the recharge just informed me that it did not solve the problem. So, he took a peek at the compressor and noticed that the clutches were not engaging. The mechanic suggested that it could possibly be an electric problem. But wasn't sure... He mentioned that the A/C fuse was good, and that he did not know if there was anything else electrically that could be preventing the clutches from working. He indicated that it could possibly be related to the A/C switch mounted in the dash??? Any advise would be really appreciated.

[DanDombrowski]

Hate to break it to ya, but its probable that the thing is out of refrigerant. Most newer cars will keep the compressor from engaging if the system is too low. You can test this easily by testing the wire that goes into the compressor with a volt meter. If it has power, but no clutch, chances are its empty. If no power, its electrical.

Hope this helps.



I am picking my car up this evening after the shop is done putting the finishing touches on my new paint job. Yippy!!! Obviously, I am going to want to show her off. Hence, my dilemma... Prior to dropping her off I learned that my A/C was not working properly - only blowing hot air. And since it 90 degrees outside, I need help. I had asked some questions on this forum last month, http://www.bimmer.info/forum/showthread.php?p=28297&highlight=a%2Fcand and based on the responses the first thing I decided to do was have the A/C system recharged. Consequently, I found out that my auxiliary fan was not working. So, I bought the replacement ballast resistor for the aux. fan and picked up a new aux. fan switch socket (figured I'd replace it while I was doing A/C maintenance). I have plans to replace them this weekend. Anyway, the mechanic that did the recharge just informed me that it did not solve the problem. So, he took a peek at the compressor and noticed that the clutches were not engaging. The mechanic suggested that it could possibly be an electric problem. But wasn't sure... He mentioned that the A/C fuse was good, and that he did not know if there was anything else electrically that could be preventing the clutches from working. He indicated that it could possibly be related to the A/C switch mounted in the dash??? Any advise would be really appreciated.

[NoSpeedLimits]

Not being very familiar with A/C systems, I hate to ask but I gotta satisfy my curiosity...how can the system be out of refrigerant? I thought recharging an A/C system did ensure the system was full of new refrigerant? I didn't specify originally because I always feel that I am giving too many unnecessary details, but the mechanic told me that he drained the system and then refilled the system. Is recharging something totally unrelated to the refrigerant?

And after I borrow my buddies volt meter, where would a A/C ignorant person look to find the switch wire?? Or better yet, were should I tell my mechanic to check. Digital photos would be a nice touch... ;)

Thanks for your help.

[DanDombrowski]

If I'm not mistaken, its the green wire in this picture. If its not, there should be only one wire going to the A/C compressor.

Recharging the system will fill it, yes. If it has a leak, however, the system can empty rather quickly. As far as checking to see if the system has refrigerant, the shop you go to will have no problem doing that, usually for free.

I'm not saying that because it doesn't come on its empty, I'm saying that if its empty, it won't come on.

I just did this troubleshooting on my Dad's Honda where they told him he had to pay a lot of $$ for an electrical diagnosis. A quick check of that wire revealed power to the compressor clutch, so we knew to look elsewhere. I doubt that testing the wire will give you a solution to your problem, but it WILL tell you if the problem is electrical or mechanical, and that will help a lot.

Since you said you're not that familiar with A/C systems, I guess I should add that the car needs to be running with the A/C on for you to check power to the wire.



Not being very familiar with A/C systems, I hate to ask but I gotta satisfy my curiosity...how can the system be out of refrigerant? I thought recharging an A/C system did ensure the system was full of new refrigerant? I didn't specify originally because I always feel that I am giving too many unnecessary details, but the mechanic told me that he drained the system and then refilled the system. Is recharging something totally unrelated to the refrigerant?

And after I borrow my buddies volt meter, where would a A/C ignorant person look to find the switch wire?? Or better yet, were should I tell my mechanic to check. Digital photos would be a nice touch... ;)

Thanks for your help.

[NoSpeedLimits]

Thanks, and nice picture! My mechanic was asking about the location of a low pressure switch. He claimed most cars have one so that you can check to see if the refrigerant is low. So, does my car have one and if so, where can I tell him to look.

Also...I am afraid to ask for fear that the answer will result in an expensive repair. But, since today is pay day, I figured I better know if I should start saving. If there is power at the compressor, then as you indicate there is probably a mechanic problem...what kind? And, does it automatically mean the compressor needs replacement?

[DanDombrowski]

Not sure what to tell you about the low pressure switch, the most I've ever gotten into A/C work is buying that gauge thingy at wal-mart, hooking it up, and seeing if the needle is in the green, yellow, or red range, thats the only method I'm aware of to test to see if the system is full.

As far as the compressor needing replacement, its certainly possible at that age, but I wouldn't declare that the problem just because it isn't turning on. The problem could be as simple as a small leak in a hose thats causing the refrigerant to leak out, or it could be a bad compressor, you're just going to have to run through the steps of troubleshooting it.

Now I'm going to give you some hints on how you can test a few things in your A/C cheaply and by yourself, but remember, the system can build up some pretty high pressures if you're not careful, so don't say I didn't warn you. Fortunately, since you have a 94, you should have the R134a system. Better check that to be sure before doing any of this, or you could just have your mechanic do it, in any event, here is how to analyze what you have.

You can go to wallymart and get a can of R134a refrigerant with the reuseable filling system (tube, connections, and gauge) for about $20. If you can, get one where the can has the UV dye in it. If not, it might be another $4 or so. So you want to read all the directions and connect the gauge to the low pressure side of the system at the connections I mentioned earlier. Check a bentley to be sure. Now, this should tell you if the system is low or not. If its low, you can fill the system back to normal. This is actually a pretty common DIY procedure and is a good skill to have for pretty much every car.

Here's where you get into the analysis:

Was it empty (or too low a pressure)? If yes, you probably have a leak since you said the mech just filled it.

Does the system turn on when its filled? If yes, again, you probably have a leak, and the low level of refrigerant is what is causing the compressor not to turn on.

How long does the A/C work for if it does come on? 1 hour? 1 day? 4 days? This will tell you how fast of a leak you have, if you have one.

Now lets assume it was low. You've filled the system and the A/C comes on and blows cold. By tomorrow, its warm again. Now is when you take a UV light, like a blacklight (I think) and look in the engine bay for the glowing residue of the UV dye in the can of refrigerant you bought. This should help you find your leak, if you have one.

Now lets assume that the system ISNT low. If the system has a decent amount of charge and you have power to the compressor and its not turning on, this is where my experience runs out, I'm sorry to say. If I were to venture a guess, I would say a bad compressor. This is where some of the professional mechanics can offer some suggestions.

Even if you don't like to do a lot of work on your car, for about $25 you can gain a lot of experience about A/Cs work, and can save you a lot of professional troubleshooting. These are the same instructions I gave my father (a civil engineer, or as we mechanicals call them, the engineers that work on stuff standing still), who knows nothing about cars, and we found the leak pretty easily. Just be sure not to connect to the high pressure side and not to overfill and you should be safe.

Whew. Am I done yet? Anything I missed?

[sbcncsu]

I am picking my car up this evening after the shop is done putting the finishing touches on my new paint job. Yippy!!! Obviously, I am going to want to show her off. Hence, my dilemma... Prior to dropping her off I learned that my A/C was not working properly - only blowing hot air. And since it 90 degrees outside, I need help. I had asked some questions on this forum last month, http://www.bimmer.info/forum/showthread.php?p=28297&highlight=a%2Fcand and based on the responses the first thing I decided to do was have the A/C system recharged. Consequently, I found out that my auxiliary fan was not working. So, I bought the replacement ballast resistor for the aux. fan and picked up a new aux. fan switch socket (figured I'd replace it while I was doing A/C maintenance). I have plans to replace them this weekend. Anyway, the mechanic that did the recharge just informed me that it did not solve the problem. So, he took a peek at the compressor and noticed that the clutches were not engaging. The mechanic suggested that it could possibly be an electric problem. But wasn't sure... He mentioned that the A/C fuse was good, and that he did not know if there was anything else electrically that could be preventing the clutches from working. He indicated that it could possibly be related to the A/C switch mounted in the dash??? Any advise would be really appreciated.

Maybe this is too obvious:

How did he recharge it if the compressor wouldn't engage?
How could he read the high and low side pressures without the compressor running?

Answer: He couldn't have.

The low pressure switch is probably not making due to the low refrigerant. To check, simply jumper it with a paperclip. It should be located on top of the receiver dryer (I am not sure, I no longer have my e34 so don't quote me on that). If it isn't there, it will definitely be in-line somewhere on the low side of the system.

Good luck,

I hate A/C work....

[DanDombrowski]

Scott is probably correct about it being somewhere near the receiver dryer, that is where it is on my Volvo, however, I was hesitant to suggest jumpering this if the system is low because I honestly don't know what kind of damage it could cause to the system, running it without refrigerant (and thus running without lubrication). Perhaps it will be perfectly fine, but I don't know, and now I'm asking.

Now, as far as charging it without the compressor running:

If he's a competant mechanic, and I'm going to assume he is, we'll say he's using all the proper tools and methods for filling the system at the low pressure side. If you start to flow high pressure R134a in from a can or resivoir or something, the pressure will increase until the switch does make contact and the compressor starts and the refrigerant flows through the system, allowing further filling. If it doesn't, well, I don't know what would happen, and I don't really want to either.

Am I wrong in assuming this is a normal procedure for filling a system that is too low to allow the compressor to come on?


Maybe this is too obvious:

How did he recharge it if the compressor wouldn't engage?
How could he read the high and low side pressures without the compressor running?

Answer: He couldn't have.

The low pressure switch is probably not making due to the low refrigerant. To check, simply jumper it with a paperclip. It should be located on top of the receiver dryer (I am not sure, I no longer have my e34 so don't quote me on that). If it isn't there, it will definitely be in-line somewhere on the low side of the system.

Good luck,

I hate A/C work....

[NoSpeedLimits]

First, thanks for your time and the detailed response. Second, to give you an update. I questioned my mechanic about the systems pressure. He claimed that he checked the pressure prior to draining and replacing and said that it was good. I am a bit confused as to why he replaced it when it was supposedly good??? I believe he mentioned something about doing it as a precaution. Does anyone have the recommended hi and low pressure numbers available??? I don't remember the numbers my mechanic rattled off but I would like to compare them the next time I see him. Otherwise, I checked the fuses and did not notice any bad ones, plus the horn worked fine. Unfortunately, I run out of time so I did not get a chance to test for power at the compressor. Hopefully, I will fine the time on my next visit to the shop. And, I also want to question him on how he filled the system without the compressor running.

[sbcncsu]

Scott is probably correct about it being somewhere near the receiver dryer, that is where it is on my Volvo, however, I was hesitant to suggest jumpering this if the system is low because I honestly don't know what kind of damage it could cause to the system, running it without refrigerant (and thus running without lubrication). Perhaps it will be perfectly fine, but I don't know, and now I'm asking.

Now, as far as charging it without the compressor running:

If he's a competant mechanic, and I'm going to assume he is, we'll say he's using all the proper tools and methods for filling the system at the low pressure side. If you start to flow high pressure R134a in from a can or resivoir or something, the pressure will increase until the switch does make contact and the compressor starts and the refrigerant flows through the system, allowing further filling. If it doesn't, well, I don't know what would happen, and I don't really want to either.

Am I wrong in assuming this is a normal procedure for filling a system that is too low to allow the compressor to come on?

I too would hope that the mechanic was competent, however if you read this:

Anyway, the mechanic that did the recharge just informed me that it did not solve the problem. So, he took a peek at the compressor and noticed that the clutches were not engaging. The mechanic suggested that it could possibly be an electric problem.

It doesn't give that impression.

It also stated above that he drained and refilled the refrigerant. Again, all he could do is use a vacuum pump to pull the refrigerant out and then a pump to put it back. Even then, he stated that he investigated the clutch not engaging AFTER the recharge. Not so good. First things first. Find out why the clutch isn't engaging. Then worry about the level of charge in the system and diagnosis of the compressor.

[DanDombrowski]

If it has a decent charge then I see no problem in jumpering the low pressure switch to concentrate on the compressor engaging (or not engaging), however, priority number 1 is to check that power wire first to find out if its an electrical or mechanical problem, which we still haven't found out.

Now that we know that the system has a charge (or so the mechanic says), we can jumper the low pressure switch to see if we can get the clutch to engage. Before I was hesitant to suggest that without knowing that the system wasnt empty, and thus my recommendation of checking the pressures to see if the system is charged.

If you have a charged system, have electrical power to the wire on the compressor, and jumper the low pressure switch, and it STILL doesn't come on, I would diagnose that as a bad compressor (or perhaps a bad clutch in the compressor). Thoughts?

BTW, I like those wheels in your sig, Scott.

[NoSpeedLimits]

Good point, thanks. Hopefully it is just a loose wire. I can't wait to see the mechanics face when I ask him how he completely filled the refrigerant when the compressor did not operate. :) Thanks for the education. I just hope my car doesn't require a new compressor, my budget can't handle it. Fortunately, winter is just around the corner.

[DanDombrowski]

What do you need A/C for anyway? (as I peel myself off the seat). I have to get down to south florida and repair the A/C on my Volvo (have to do a r134a retrofit).

A loose wire would be a cheap fix that we always hope for. Don't get too carried away with expensive repairs until you find out the facts and make some educated decisions based on the results. Sure hope you don't need a compressor. Feel free to PM me or anything if you need more help after you finish testing.



Good point, thanks. Hopefully it is just a loose wire. I can't wait to see the mechanics face when I ask him how he completely filled the refrigerant when the compressor did not operate. :) Thanks for the education. I just hope my car doesn't require a new compressor, my budget can't handle it. Fortunately, winter is just around the corner.

[NoSpeedLimits]

UPDATE: THERE IS NO POWER at the compressor, now what?? I am partially relieved, but on-the-other-hand nervous about tracing down an electric problem; especially since the fuses appeared okay. BTW-while I was checking the fuses, I noticed slot #8 was missing a fuse, is this normal? Any pointers as to where to begin looking to find the electrical problem??? TIA.

[DanDombrowski]

Aaahh, good to see we're making progress! Now, you see where not following the correct troubleshooting steps may have led to replacing your compressor when not necessary? This is why we do things right the first time.

Electrical troubleshooting, my FAVORITE!!

Before doing ANYTHING, follow the power wire through the engine bay and make sure it hasn't worn through.

Now, First thing to do is check a bentley and find out what fuse/fuses is/are for the A/C. I wish I could tell you, but my Bentley is in Gainesville and I'm stuck at work.

Check power on both sides of the fuse block (before the fuse and after the fuse) for all fuses that go with the A/C system. If all of those work, well, then you're going to need to get a wiring diagram and find out where all the connection points are for the A/C control module.

If you can find an easy place to disconnect the wire from the compressor and hit that spot on the compressor with +12V from the battery (while the car is running), you should confirm first that the compressor WILL come on when it does get power. It would be a good idea to have an inline fuse (if possible) in this jumper wire. If it does, we can spend more time tracing down electrical woes. Make sure before you do this that the original power wire is disconnected, otherwise current goes backwards into the system, and that is no good.

Now, assuming you jump the compressor and it works, and all the fuses are good, and you have your wiring diagram, I recommend that you work backwards from the power wire in the engine bay when testing connections.

Let me know when you need more help.

[Bill R.]

the compressor if anything such as the compressor relay, low pressure switch , high pressure switch is faulty or the system is low on refrigerant.
The first thing you should do is get a set of gauges and see how much charge is actually in the system. Thats first. IF there is insufficient charge then the low pressure switch won't allow the compressor relay to energize which won't send power to the compressor clutch. There are 2 fuses that can affect the compressor relay, both f9 and f20 will keep the compressor relay from working. But first check the system pressure, regardless of what your mechanic said, take it elsewhere and just ask them to tell you the static pressure in the system. Or get some gauges and do it yourself.










UPDATE: THERE IS NO POWER at the compressor, now what?? I am partially relieved, but on-the-other-hand nervous about tracing down an electric problem; especially since the fuses appeared okay. BTW-while I was checking the fuses, I noticed slot #8 was missing a fuse, is this normal? Any pointers as to where to begin looking to find the electrical problem??? TIA.

[DanDombrowski]

Right after I posted that, I thought about the low pressure switch and realized that that may be what is causing the system not to energize, but without my bentley, I wasn't sure.

As far as the low pressure switch and the charge in the system, I was going off the assumption that the mechanic did check and charge, but you're right, he should take it elsewhere to be sure. Any thoughts on jumpering the low pressure switch Bill? I.e., any significant damage if the system is turned on on low refrigerant for a few seconds?

[Bill R.]

Therefore he's either lying or if he's a republican then he was simply mistaken. There's no point to jumpering the low pressure switch until you put some gauges on it to see if the system has any charge. If theres any charge at all he can jumper it then, running it for a few seconds won't hurt anything







Right after I posted that, I thought about the low pressure switch and realized that that may be what is causing the system not to energize, but without my bentley, I wasn't sure.

As far as the low pressure switch and the charge in the system, I was going off the assumption that the mechanic did check and charge, but you're right, he should take it elsewhere to be sure. Any thoughts on jumpering the low pressure switch Bill? I.e., any significant damage if the system is turned on on low refrigerant for a few seconds?

[NoSpeedLimits]

Thanks Bill, and Dan. I guess I will take her up to the BMW stealer sometime next week and let them check the static pressure, and give me there opinion as to what is wrong. Any idea as to what the numbers are supposes to be? Also, are the low pressure switches known for going bad on E34? If so, I can call BMA and attempt to replace it before wasting any cash at the stealer (I'd much rather throw a few bucks to BMA then the local stealer).

FYI. I questioned the mechanic again today about the pressure and he swears it is sufficient. BTW-not sure if this info. is relevant, but he also showed me that the clutch spun freely when turned by hand -- it was not locked up or frozen. Dunno know if that helps or not??

Again, thanks for all of help!

[Bill R.]

set of r134 gauges... Thats almost any shop at all... everybody has them.
Won't take them 30 seconds to see what the pressure in the system is.
ON a hot day the static pressure will be over 100 psi in the system if its charged up.







Thanks Bill, and Dan. I guess I will take her up to the BMW stealer sometime next week and let them check the static pressure, and give me there opinion as to what is wrong. Any idea as to what the numbers are supposes to be? Also, are the low pressure switches known for going bad on E34? If so, I can call BMA and attempt to replace it before wasting any cash at the stealer (I'd much rather throw a few bucks to BMA then the local stealer).

FYI. I questioned the mechanic again today about the pressure and he swears it is sufficient. BTW-not sure if this info. is relevant, but he also showed me that the clutch spun freely when turned by hand -- it was not locked up or frozen. Dunno know if that helps or not??

Again, thanks for all of help!

[DanDombrowski]

See, I tend to base my recommendations around the assumption that the mechanic performed his check correctly and that the system was running at the time in which case the most likely problem would be a wire that broke or a sudden leak.

As you and some other people have said, he can't check the pressure without running it, which is more and more calling into question the mechanics practices.

However, I am now confused.
If you just said that the mechanic can't check the high and low pressure systems without it running, how is he going to go get some gauges and check the pressure without the system running?

[Bill R.]

vary according to the ambient temperature and the temp of the car.
Heat from the radiator will indirectly heat up the condensor which will heat the contained refrigerant in the system causeing the pressure to rise.
High and low pressure are the pressure reading from the discharge side of the compressor and the suction side of the compressor when the system is running. You know what they say when you assume...:)





See, I tend to base my recommendations around the assumption that the mechanic performed his check correctly and that the system was running at the time in which case the most likely problem would be a wire that broke or a sudden leak.

As you and some other people have said, he can't check the pressure without running it, which is more and more calling into question the mechanics practices.

However, I am now confused.
If you just said that the mechanic can't check the high and low pressure systems without it running, how is he going to go get some gauges and check the pressure without the system running?

[NoSpeedLimits]

If my memory servers me, the mechanic said the systems high pressure was around 120 psi, (he possibly said 150 psi). And I think he said the low was around 80 psi. Does that sound about correct??? Either way, I'll bring her by a local shop and get confirmation on the static pressure a.s.a.p. I am still waiting on the body shop to finish detailing my new paint job -- I should have her back on Monday.

[Tiger]

Low Pressure is 34 PSI for optimal... 30 is fine also for colder A/C

[Bill R.]

hours the pressure will equalize and it will be the same high and low when checked with the car not running. If his number were for the high and low side running then its way low on the high side and way high on the low side.

You need to know the ambient temp and the relative humidity to determine what the high and low pressure should be accurately for any given time you check it.




If my memory servers me, the mechanic said the systems high pressure was around 120 psi, (he possibly said 150 psi). And I think he said the low was around 80 psi. Does that sound about correct??? Either way, I'll bring her by a local shop and get confirmation on the static pressure a.s.a.p. I am still waiting on the body shop to finish detailing my new paint job -- I should have her back on Monday.

[Tiger]

I totally agree with Bill R... get a set of gauge... it is the best investment you will make. In any case, if you bought the pro gauge with long hoses, I suggest you purge the lines before you attempt to refill it. If you are just checking the pressure, then just hook it up.

The short hoses versions you see at the auto parts store... it is short enough to not worry much.

But in any case, everyone needs a gauge to check the pressure in system when diagnosing A/C problem. I paid only $18 for a good gauge that also charges the system with spin on bottle... It only does the low side though. I will get a dedicated R134a pro gauge soon. I already got the R12/R22 but I use it for home A/C, fridge, central air, etc.

[DanDombrowski]

ok, so you want him to check the STATIC pressure with his own gauge, and then, if decent, jumper the low pressure switch and go from there? Makes sense.

Is there anything different about checking the static pressure with a handy wallymart gauge than checking the low pressure side?

Yeah yeah, you make an "ass" out of "U" and "me".

I have to go pretend to work now.

[NoSpeedLimits]

I never thought to ask weather or not he checked the pressure while the system was operational. Since the car is at a local Ford stealer getting the new paint, I assumed (I know I shouldn't assume ;) ) that they knew what they were doing. However, base on the information you've provided, I am starting to believe that he could not have obtain an accurate operating pressure since the compressor was not functioning. He did lead me to believe that he checked the pressure while it was running, I will confirm on Monday. In-the-mean-time, I will stop by the local auto store or wally-mart to look at the A/C gauges. Thanks again for your help!

Oh-BTW, I forgot to tell you what the mechanics response was to my questioning him on how he filled the refrigerant without the compressor operating. Unfortunately, the dude is soft spoken and I am forced to interpret every other word, so I cannot quote him. But, never-the-less, he mutter; by using a vacuum to relieve the system's refrigerant and by using R134a refrigerant, having the compressor operational was not necessary to get the system to full pressure. He said it cannot be done with the R12 or R(don't remember), but it can be done with the R134a. Does this sound right, or has this guy been hanging out in the paint booth too much??

[bimmerd00d]

your a/c will not kick on if the aux fan is not functioning.

[DanDombrowski]

Not true. My Aux fan does not work and my A/C works fine. By fine, I mean that its warm when the car is standing still because it has no airflow, but the compressor certainly runs.

[Tiger]

The system can be charged without car's compressor running. You have to vacuum the system... using a vacuum pump... to 30 PSI Vacuum... and then after a while to see if the vacuum holds (indicates no leak in system)... then you simply hook up the refrigerant and let the vacuum suck it in. You have to understand... the whole system need only like 2.3 pounds... depending on what car... bigger car takes a bit more.

As long as there are minimal pressure to get by the low pressure sensor, the compressor can run... and then add more if necessary to achieve 34 PSI... with windows closed... run at least 5 minutes to determine the actual final pressure...

The most important of all is that the aux fan must be working at the time of final adjustment in pressure. Otherwise, you will never be able to get the accurate pressure... (pressure will be much higher if aux fan is not working) and it totally screws up the final reading because you think it has too much R134.

[Tiger]

This is correct... aux fan can be dead and A/C compressor will runs as long as the low pressure sensor says it is okay... or the high pressure sensor says okay too.