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

[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.