AC PSI Interpretation

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Gebo

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Gone for a week on vacation. Come back and get in the car that stayed behind and didn't get driven for a week. No prior notice to the AC getting worse before we left. Now, AC not working. It abruptly stopped working. Fuse good, compressor coming on, only ambient air from the vents.

Hooked up manifold gauges and got this reading with engine idling and AC running for 15 minutes:
115 PSI Low pressure side
150 PSI High pressure side

(The low pressure side started out at 85 PSI when first started engine)


After running for 15 minutes and turning car off I get these pressures:
125 PSI low pressure side
135 PSI high pressure side


What is your expert diagnosis? What would you begin with?
 
The pressures will equalize when it's shut down.

Was the compressor running when you measured the pressures? Your low side is very high and the high side is very low.

Bad compressor.
 
Last edited:
Compressor was running

Hooked up manifold gauges and got this reading with engine idling and AC running for 15 minutes:
115 PSI Low pressure side
150 PSI High pressure side
 
Which vehicle?

Could be a bad compressor or the expansion valve has a problem, as in is wide open.
 
Last edited:
Just thought it interesting it was working fine before it sat for a week....
 
You need a visit to an auto shop that repairs Air Conditioning units. Sounds like the compressor is not pumping right - valves?

They have the equipment for checking it over.
 
It does use an expansion valve instead of a orifice tube but really neither is that likely to fail.

I'd still go with the compressor. A good a/c shop can test it.

If the compressor did fail it'd be a good idea to flush the system - just in case.
 
It appears to be either the expansion valve or the compressor. How do I determine which it is between those 2 choices?
 
If the end of the compressor is turning that means it is engaged, correct?
 
There's a clutch, no? The end will always idle, but the compressor may not be clutched in. Do this, start the car, everything off, then watch the compressor while you have someone start hvac and turn AC on. You should hear a click when the clutch engages.

The shaft could be broken in there so it spins but doesn't compress.
 
The end of my compressor doesn't spin unless the AC is turned on
 
Your compressor has got to be toasted. A wide open expansion valve or even an orifice with the inner metal tube blown out (seen that) will still provide enough resistance to give you a wider pressure spread. Any needle bounce on your gauges when the compressor is on?
 
No needle bounce. Rock Steady.

I'm taking it in tomorrow. I'm betting expansion valve. We shall see.
 
Originally Posted By: Gebo
No needle bounce. Rock Steady.

I'm taking it in tomorrow. I'm betting expansion valve. We shall see.


Well good luck with it. Please post when you get a diag .
 
Except non-engaging clutch, blown compressor or the blown expansion valve *will* make the needle move.

Do this. Find the low pressure cutout switch and try to jumper/un-jumper it and verify that you hear the loud click from the compressor clutch.
 
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