525i A/C problems...

[Spud]

I need some help on an A/C problem I'm having with my 92 525i

I had the A/C system checked, flushed and topped off with fresh R12 and the requisite amount of oil. It blows cool although at start up the idle speed sometimes hunts between 500 and 700 rpm until the car has reached operating temperature. Once up to temp everything seems fine, including the secondary fans turning on if necessary.

I've had the fuel injectors serviced, replaced all the fuel hose, fuel filter&air filter, plugs and plug-to-coil connectors so I think my fuel system is OK.

I did use my PAEKE tool to read the codes and got a 55, "A/C compressor" which is a bit vague. I tried to do a stomp test, but couldn't really make sense of what I was seeing. Probably didn't help trying to do this in the parking lot at lunch time…

Anyway, I guess if the Peake tool is correct then the options according to Bentley are "A/C compressor cut off" and "A/C compressor signal". If this is the case then what do I need to look for since to me everything seems OK.

I suppose I can check the pressure switch on the drier and take it from there, but any other suggestions, or weak points in the system, would be appreciated.
:(

[shogun]

including the secondary fans turning on if necessary. ?

I thought that runs always when a/c is on, either on low or high.
Last Saturday a friend had a prob with this, was only running on low. I replaced the relay and all was o.k.

[Spud]

Shogun,

Thanks for the suggestion. I guess I can get out there with my multimeter and check out going on...

Spud

[Spud]

OK, I checked out the system and it looks like the aux fan resistor is shot.

The relays, drier pressure switch and connectors all check out. Since there's voltage at the fan connector and the fan runs in "high speed" I think the resistor is open circuit.

I'm going to order a replacement wire wound resistor from Mouser Electronics (www.mouser.com), part no. 284-HS100-0.5. This is a 100 watt, 0.5 ohm resistor and whilst the mounting is a little different at $16 its got to be worth a try. I'll reset the codes and see what happens.

Thanks again to Shogun for the suggestion.

I'll try to post a reply following the fix, but it might take a while...

[Spud]

Just an update to say that the wirewound resistor that I ordered from Mouser Electronics (www.mouser.com), part no. 284-HS100-0.5. seems to work just fine as a fix for a failed aux fan ballast.

I had to modify the original mounting bracket and take some material off the resistor flanges, but since its rated for 100 watts and is considerably larger than the original I think it should be OK.

I guess its up to you to decide if the $$ savings are worth the extra hassel of fitting. I also managed to replace the resistor by working through the access panel next to the fog light. It was tight squeeze but workable, just...

[CBC]

Spud - Can you help me with a few more details on this resistor you replaced? I seem to have a similar issue with my aux. fan, but in reverse. Mine only works on low. This seems to be affecting the A/C cooling at higher interior fan speeds ( speed #3 and 4 on the control panel). I looked up the part number on the mosser site and found it no problem. Did you use the Bentley repair manual to determine how the replacement should go? I've got one on order, but without some directions, I have no idea where to actually find the resistor. Secondly, will this new resistor correct the fan problem I have, given that I only have the low speed working? Thanks.

[winfred]

the resister is only to slow the fan and lower it's power consumption/noise during normal operation, if it's not kicking into high it's, not needed, bad high speed relay or bad high pressure switch, those are the most likely issues


Spud - Can you help me with a few more details on this resistor you replaced? I seem to have a similar issue with my aux. fan, but in reverse. Mine only works on low. This seems to be affecting the A/C cooling at higher interior fan speeds ( speed #3 and 4 on the control panel). I looked up the part number on the mosser site and found it no problem. Did you use the Bentley repair manual to determine how the replacement should go? I've got one on order, but without some directions, I have no idea where to actually find the resistor. Secondly, will this new resistor correct the fan problem I have, given that I only have the low speed working? Thanks.

[Spud]

Spud - Can you help me with a few more details on this resistor you replaced? I seem to have a similar issue with my aux. fan, but in reverse. Mine only works on low. This seems to be affecting the A/C cooling at higher interior fan speeds ( speed #3 and 4 on the control panel). I looked up the part number on the mosser site and found it no problem. Did you use the Bentley repair manual to determine how the replacement should go? I've got one on order, but without some directions, I have no idea where to actually find the resistor. Secondly, will this new resistor correct the fan problem I have, given that I only have the low speed working? Thanks.

CBC,

As Winfred said it looks like your low speed circuit, and therefore the resistor, are OK.

You can easily check both the low and high speed operation of the fan by removing the relays and jumping the connections. You'll need some pretty thick wire, a paper clip won't cut it...

The high speed relay, in my car was orange, and can also be identified by the fact that it has 4 prongs - the normal speed relay has 5 and was grey. Unplug the relay, take your jumper wire and carefully connect sockets numbers 2 and 6 together (look for the numbers on the relay socket). Take care because the fan motor induction will cause the connection to spark a little as the contact is made.

If the fuse, F25 (30 amp), wiring and aux fan motor are good then you're hear the fan run at full speed. Remove the link and the fan should stop. Repeat the process with the low speed relay, the connections are the same, and you should hear the fan run again albeit slower. If both these tests check out then its probably the relay or the relay control.

You can check the relays on the bench, but you'll need a power source, or a means of connecting the really coil contacts to 12 volts and DVM to measure the contact resistance as the relay coil operates. It should go from a high to a low reading. If the continuity tests passes this still may not be enough to prove the relay is in good condition since as the relay ages and the contacts wear the contact resistance increases and makes the operation under full load potentially unreliable. Its generally not a good idea to use a car battery for testing relays unless you fuse your hot test leads as the current capacity of the battery is significant and if something's wrong it can get messy very quickly.

If the relays check out along with the wiring then you'll need to use a DVM to check the relay control signals. Check F29 first (7.5 amp) since this is the relay coil supply voltage and if this is OK you should be able to measure approximately 12 volts on contact 8 of the high speed relay and contact 4 of the low speed relay. If these voltages check out and the relays are good plug them both back in and remove the temperature switch which is mounted on the passenger side of the radiator and has three wires connected to it. Pin 1, the brown wire, is ground and you should be able to take the same wire you used in the relay test and carefully connect this to pin 2 the violet/grey wire. This should operate the normal speed relay, which you should hear click, and the fan should run. Remove the short and the fan should stop. Repeat the test by shorting pin 1 to pin 3, blk/gry/yel and the high speed relay should operate and the fan should run at full speed.

Finally if all this checks out and the A/C still doesn't work then you'll need to check the pressure switch and climate control signals. The pressure switch is located on the A/C drier located under the windscreen washer bottle. Check to see if you have continuity between the connector pins where the blk/gry and blk/red/yel wires plugged in. This should be 0 ohms. If this is OK then it may be the climate control compressor control output which isn't turning on the normal speed relay…

I hope the above makes sense and I strongly recommend, as many others do, to invest in a Bentley manual. The wiring diagrams are invaluable. Also, if you don't feel comfortable checking out wiring then don't. You can cause a lot of problems by melting wires as you can probably appreciate. I'd suggest getting some help to check out the above and then if you still can fix it you can approach a shop safe in the knowledge that you've tried all the obvious stuff. You may even find that the systems not working because its simply low on refrigerant…

Spud