AC Compressor question [Expired Topic]

[unplugged]

OK, after reading the posts here I decide to upgrade from R12 to R134a on my 93 burb, thinking that the lack of cold air is because of low refrigerant level.

Wrong. I notice that the compressor is not operating when the AC is on. Is there a way to troubleshoot this or am I stuck with trial and error component replacement?

btw, it has rear ac too.

[MrShorty]

There's a low pressure cut off switch in on the system that prevents the compressor from coming on if the Ac pressure is below a certain value. Basically, the compressor may not be coming on because of low refrigerant level (the same diagnosis you started with). I would think one of the first steps in diagnosing this would be to put a pressure gauge on the system and see what your charge looks like.

[84fiero123]

Put a test light on the plug going into the clutch on the compressor. then have a helper turn AC on.

You should get a light from it then, if not you may be so low the system will not allow it to turn on. A safety feature.

If the system is that low you may have a leak somewhere.

You should have the system evacuated before change over, that way you can be sure you don’t have a leak. If it holds the vacuum it’s cool. Then you can refill with the new coolant.

[unplugged]

Pressure in the 'green' zone on the DIY gauge that came with the refill kit. I checked the voltage at the ac plug, and there was zero volts when the AC switch was on. With the system off there is no pressure at the low or high side. Looks like I have a leak. The instructions say to have the AC running when filling, but since the low pressure switch is shutting the compressor down, I seem to be in a catch22 situation.

[unplugged]

Just put a new compressor on and took it to the shop to have it pumped down , leak checked and refilled with fresh R12. Skipped the conversion to R134A since the price was only $38/lb for R12. 4.5 lbs total to fill. Cold stuff coming out the vents! Front/rear ac works great now!