A/C stopped working, high pressure on low side

[Lancer521]

I've been driving my '03 Vibe GT for about 2 and a half years without any problems with the A/C, nor have I added any refrigerant to the system. Randomly last week it stopped blowing cold air - it just blew outside temp air. When I click the A/C button, my RPMs change slightly, so something is happening. I hooked up one of those dinky gauges from AutoZone to see the pressure on the low side and it was higher than the gauge would read. I even used a separate gauge to get a second opinion.

Any ideas as to why I would have high pressure on the low side? Or more generally what could be wrong? I've read a bit and seen some talk about a valve within the compressor being bad... but I haven't seen much concrete information on it, just that it has been mentioned.

Your help is appreciated!

[SlammedNiss]

I don't know much when it comes to A/C systems, but I had to change out the relay under the hood that controls the compressor last week. It had started being intermittent about a year ago, and finally stopped blowing cold altogether a couple weeks ago.

[tpollauf]

You need to visually watch the gauge all the time and have someone turn on/off the AC and then observe. If you're recording high pressure on the low side, then the compressor is probably not coming on at all, thus you're seeing the pressure of the system in the off state.

[gtv237]

I've seen this a few times. It's caused by a part in the compressor. Replacing the compressor will fix the problem. Of course it's always a good idea to go ahead and replace the orfice tube while you have the system decompressed.

[cptnsolo77]

I had the same problem as you did, my low side was HIGH and high side was LOW. Turned out to be a bad compressor. Straightforward repair, just remove the fan assembly and you will have plenty of room to work. Cheapest I found was on amazon for the OEM AC delco compressor. Dont forget the filter dyer. That can be made easier to replace by removing the left grille insert

[jayoldschool]

Just found out that mine's not working as well. 04 base. Relay swap wouldn't work, checked low side pressure with car off, it's about 25. I'll test the compressor clutch next!

[tpollauf]

checked low side pressure with car off, it's about 25.

Wooooaaa .... we have a problem here If your "static" pressure (that is, at rest OR in the off mode) is only 28 psi then you have a LEAK! Any system in any car which uses R-134A and is properly charged, will register 80-100 psi with NOTHING running at all. The car off! It will measure this pressure ANYWHERE in the system (hi side vapor/liquid, low side vapor/liquid). So for you to be measuring only 28, it is so low that the low side pressure switch is barely making. In your case it probably is NOT made and thuis nothing will work at all. I believe 30psi is the cutoff point where it shuts down the system.

[jayoldschool]

I'll check it running on the low. I agree that it may be low enough to not engage the pressure switch, I just threw the gauge on it to make sure it didn't leak out the complete charge (and it hasn't). I don't think the low should be reading 80-100 with the car off... what do you base that info on? I have full gauges and r134a in stock so I can add a bit to see if it will start to cycle.

[tpollauf]

I don't think the low should be reading 80-100 with the car off... what do you base that info on?

Simple answer to that question. Your car, when sitting there at rest and cold, contains roughly 26 oz. of R-134A in all the piping and components. Now your can of Virgin R-134A sitting on the shelf also is sitting at rest and doing nothing. Put a gauge directly onto the can of refrigerant and record the pressure. IT will be 80-100psi give or take. Now go to your COLD car just sitting there and measure the pressure in it's system. IT too should read 80-100 psi. If not then there is a leak and most of the refrigerant is gone. Don't let "low side" or "high side" confuse you. When checking system pressure, there is NO high or low side. The system is in a state of equilibrium where all pressures are the same. They only change once the compressor is engaged. Hope this helps1