Automotive Air Conditioning Information Forum

My 2008 with the 5.7L is acting very strange to me. When the AC is running, sometimes, it will vent at the high pressure bypass on the compressor. It only seems to do this when the ambient temps are above 90 or so. Below that the AC seems to work pretty well and blow cold. I replaced the compressor last year because of this issue, and the compressor was making a lot of racket, and all seemed well enough for a while. I only changed the compressor, nothing else. Pulled the vacuum overnight and filled the next day to the pressures per the r134a charts.

So as this happens intermittently, and seems to be caused by rising pressure from ambient temps I am left thinking about it being a couple of possibilities.
1. The pressure switch is failing to cut off the compressor at high pressures.
2. The expansion valve is sticking causing the pressures to spike and the compressor to vent. However, this leads me back to #1 as I need to turn off the AC inside or it will keep venting over and over.

Anyway, as you can probably tell, I'm not a professional, but I am trying to learn.

I'd first ensure that your fan clutch or electric condenser/radiator fan(s) are operating properly.

Interesting youemtioned that. I just discovered some, if not all, the foam blocking between the condenser and the radiator is missing. I assume this is there to ensure proper air flow when sitting still. I'm looking up part numbers and am going to get the bits on order now. Probably going to be a real pain to install them. I also wonder if installing a pusher fan onto the condenser would be a better solution. Just run it off a relay that gets a signal from the compressor clutch?

If you're charging by pressures instead of by weight, you've most likely overcharged the system, causing the safety valve to vent refrigerant.

JohnHere wrote: Mon Jun 16, 2025 3:44 pm If you're charging by pressures instead of by weight, you've most likely overcharged the system, causing the safety valve to vent refrigerant.

Always charge by specs. We are so far from the retrofit pressure charts at this point, IMO.