Air-con pressure high / low side

[CoolHands]

I had my air con recharged as it had stopped working (blowing cold). The machine self-does everything and I saw it’s programme evacuate the gas, then do a 5 min test of pressure etc and was perfect (no leak). Eventually it then added new amount of refrigerant after doing its automatic tests.

My question is, why does both the high and low pressure gauges record the identical pressure (110psi)? - do I need to be concerned. I don’t know if this is normal and the operators were not helpful/didn’t know anything worthwhile. Note, this is as the machine finished, not with my vehicle engine running so maybe the info below is irrelevant as I assume those are operating pressures with it running?

From an online webpage about my model of car (Mini Cooper) it states the below.

Expect a static system pressure of 75 psi. The compressor should come on with a minimum of 45 psi. When testing, the following pressure scenarios can be used to point you toward the issue (85 degrees F ambient temp):
Normal low pressure (21-35psi), Normal High pressure (199-275psi)
High and low pressure needles bouncing from low to normal indicates moisture in system.
Low pressure reading Low side (7-14psi), Low pressure reading High side (99-142psi)
Low refrigerant charge
Poor refrigerant circulation
High pressure reading Low side (30-50 psi), Low pressure reading High side (280-355psi)
Over-charged system
Expansion valve stuck open
Air in system

[CoolHands]

Hmm seems from reading, the static pressures (engine off) should be relatively equal, but it depends on ambient temp. Mine at 7.5bar would be expected in 34+ degrees C heat. Since it was only 24 degrees according to a r134a pressure chart it should be about 4.3 bar.

But I don’t think this is was adjustable by the operator.

So probably ok, maybe bit high, but high and low should be checked with engine running which was not done.

[Jaz2000]

May sound like a stupid question the engine was running, but was the a/c turned on.

[ARHarh]

In very basic terms ac is just a loop of pipes and stuff. So if the engine is not running and AC is off, the pressure in both sides will be the same. Only if running will the gauge after the compressor show a higher pressure. I have not read this but the pic looks good. https://www.coolcaraircon.co.uk/maintain-your-car-...

[CoolHands]

Jaz2000 said:

May sound like a stupid question the engine was running, but was the a/c turned on.

No in that pic engine was not running. So just the ‘static’ pressure which I understand is correct that both sides are equal. He didn’t check pressures with engine running either before or after the job, just hooked up the machine which did everything automatically.

I think on balance, I’ll leave it, it seems ok!

[ARHarh]

Yeah They don't normally start the engine and AC until the machine is disconnected, I guess the gauges are for diagnosing a faulty compressor. They should have checked the AC was chucking out cold air at about 10 degrees c or less though.

[richhead]

The pressures will always be close if the compressor isnt running. As long as its cold all good.