# What should a/c low side/high side pressures be after weeks of non-use?

I removed the compressor clutch relay last week when I began noticing severe engine bog when the compressor engages. I'm Hopeful that I can minimize further damage and salvage whatever I can. Now it's a week later and I finally had time to hook up my gages (compressor still disabled via clutch relay removal). Low side and high side both read ~60 psi. I know hi should be 198-228 and low 22-36 psi, but I assume that is when the system is running. So my question is, would a good system be expected to maintain those pressures after days/weeks?

## 1 Answer

If you are asking if the pressures should remain as low/high for several weeks, no. It's not going to do that. There's two principles with an A/C system at play here. In order for the A/C to work, there has to be a high pressure side where, after the charge is compressed is run through the condenser and is cooled (while still at pressure). Then the low side, where the cooled refrigerant has a chance to expand and thermodynamics has a chance to do it's thing and this cools the inside of your car. The second part is there has to be flow in order for this these things to happen. Refrigerant has to be able to flow through the system. If it doesn't, you'd never get the first part to happen. Due to this, given time, refrigerant is going to equalize between the low/high sides over time.

Something to think about ... when, after running your A/C system and you shut your engine down. If you've listened to your A/C system after the fact, you'll hear it hissing. This is the refrigerant equalizing through the system. Really, it won't take it too long for the equalization to occur. Probably going to be equalized within a 1/2 hour of shutdown.

• Thanks! I wonder if you could advise me on something further. What is the best way to diagnose if the compressor has simply failed versus self destructed with metal fragment release? I'd like to determine that myself before to make sure I buy exactly what I need before getting started. Will it be obvious to whoever I take it to for gas removal? Dec 8 '17 at 15:51
• Please ask that as a new question! :o) Dec 8 '17 at 16:28
• I did. Here it is.(mechanics.stackexchange.com/questions/50182/…). Dec 8 '17 at 18:32
• If the system uses r134a, equalized pressures at 75° should be 75 psi. At 70°, 70 psi. Feb 16 '18 at 23:52