boring AC question- could the compressor run w/o pressure?

[AllanS]

I finally got around to futzing with the ac problem, and did what Winfred suggested (about a month ago), and jumpered one of the connectors on the drier switch while the car was running and the ac was turned "on".

The compressor instantly turned on! I went in the car, and bam, cold air right away. I played with it while the jumper was still there, and it worked flawlessly.

Now I'm wondering... is it safe to drive around with this jumper there, bypassing the low pressure switch? Is it possible that the pressure really is low, but enough for me to get cold air? Or is it most likely a faulty sensor? Should I jumper the white aux fan connector as well?

The sensor body itself is cracked and looks pretty beat up, but I'm not sure what bearing this has on it.

Thanks!
AllanS

[mike wong]

did you see a lot of bubbles in the sight glass?
or just gas? all clear means it's liquid.

you really need to hook up pressure guages.
then you can determine if you have a bad sensor of not.

the low pressure switch protects the compressor from overworking burnout.

if you are in the SF bay area, email me offline.

[632 Regal]

low pressure switch also prevents it from burning out from lack of oil lubrication that should be floating in the charged freon.

[AllanS]

Should I not be seeing bubbles if it's working properly? Do I need a special gauge to test the pressure of the system?

Thanks,
Allan (in NY unfortunately!)

[Bill R.]

leave it jumpered then the compressor doesn't shut off when the pressure gets too low and when the pressure gets too low and the return gas gets too cold then it turns to liquid coming back to the compressor and when that happens the compressor won't compress liquid so you break all the valves and pistons in the compressor..... Also what Jeff was saying is that the oil used in airconditioning systems circulates through the system in the form of a mist and the refrigerant gas carries this oil around the system and back to the compressor, If you don't have sufficient charge in the system then the oil will get trapped in various places in the system such as the condensor and it will all get taken out of the compressor but won't return since there isn't sufficient volume of gas to carry it back to the compressor, when this starvation happens the compressor will run out of oil and sieze and break just like an engine does when it runs out of oil, and yes you need a gauge set to accurately check the pressures in the system.






I finally got around to futzing with the ac problem, and did what Winfred suggested (about a month ago), and jumpered one of the connectors on the drier switch while the car was running and the ac was turned "on".

The compressor instantly turned on! I went in the car, and bam, cold air right away. I played with it while the jumper was still there, and it worked flawlessly.

Now I'm wondering... is it safe to drive around with this jumper there, bypassing the low pressure switch? Is it possible that the pressure really is low, but enough for me to get cold air? Or is it most likely a faulty sensor? Should I jumper the white aux fan connector as well?

The sensor body itself is cracked and looks pretty beat up, but I'm not sure what bearing this has on it.

Thanks!
AllanS

[AllanS]

So the sight glass really isn't a great way to gauge the pressure, correct? Do you know if a gauge set is expensive to buy? Would an autoparts store have it or am I going to have to have a shop look at it?

Allan

[AllanS]

I just looked at the sight glass when the compressor is running, and when it turns on, there's a lot of bubbles, but they clear up after maybe 10 seconds, and then it's clear.

[632 Regal]

however the site glass is theer for a reason. A few years back while getting my certification in this (for the mere reason of buying improper freon to replace R-12..another story) the site glass does work, in theory if the oild was never lost in the system and air was not ever introduced. The proper way to use the glass upon charging the system is to attemot to charge it on an 80 degree day, all windows ope and AC fan on high, add freon until the moment the bubbles go away, un-jumpered for you!, and can sustain running with no bubbles appearing.

[632 Regal]

however the site glass is theer for a reason. A few years back while getting my certification in this Automotive HVAC (for the mere reason of buying improper freon to replace R-12..another story) the site glass does work, in theory if the oil was never lost in the system and air contamination was not introduced. The proper way to use the glass upon charging the system is to attempt to charge it on an 80 degree day, all windows open and AC fan on high, add freon until the moment the bubbles go away, un-jumpered for you!, and can sustain running with no bubbles appearing. Make sure the compressor cycles and the bubbles remain gone during cooling.

I am not disagreeing with George because a gage set is indespensible if the temperatures arent exact and if you are still having problems there is no way a site glass can give you a clue about where to look next. These methods were used for many years and do work however they may not be at the best pressure for economy and cooling.

Now I want to watch my site glass and run the AC to see if this is true but it it 70 degrees and should be solid with no bubbles if correct.hmm... BRB

[632 Regal]

now I am wondering if the ambient temperature was say...100 degrees if there would be bubbles...damn internet courses. Going to have to break out the real HVAC book from MANY years ago.

[Bellicose Right Winger]

Bubbles when AC first starts is OK as long as they go away. Another quick check is to inspect/touch an exposed metal part of the large diameter suction line from firewall to compressor. It's right next to line with sight glass. If you've got a full refrigerant charge and system is otherwise working, this line should be cold (~50F) and, if humidity is high, it'll be sweating extensively.

The pressure switch on my '90 535 has two connectors. How do you know you jumped the low pressure switch and not the high pressure switch?

Paul Shovestul



I just looked at the sight glass when the compressor is running, and when it turns on, there's a lot of bubbles, but they clear up after maybe 10 seconds, and then it's clear.

[AllanS]

Is it true that with r134, you can't use the sight glass as accurately as with r12?

If I get bubbles at start up, but they disappear right away, what do you think that would mean?

[AllanS]

One switch (the white one) just turned the aux fan on (I jumpered this one first) and the other (black) switch made the compressor clutch engage (these were jumpered while the ac was "on" so everything started right away- I wasn't jumpering the actual compressor itself).

Those were the only 2 switchs/connectors there, coming off one sensor which was screwed into the drier.

I'm going to have a local shop do a pressure test to see if it really is ok or not- if it's fine, then I'll probably just order a new sensor and hope it works.