Chevrolet Malibu Forums banner

Quick question about ac pressure Solenoid.

762 Views 12 Replies 4 Participants Last post by  Astroman
Hey all I'm new to this forum.

I'm trying to help a buddy fix his a/c. So the first issue I saw was that the pressure was equal between low and high. The clutch doesn't engage either.

Just curious, I heard the ac pressure solenoid often goes on these. Would that cause this equal pressure issue? I know it would definitely prevent the Compressor from engaging.

Thanks for any help!
1 - 7 of 13 Posts
Pressures equalize with system off for a while. Need at least 40 psi. for clutch to engage.
The pressure is 70psi both sides, so there's enough to start the clutch. And it's weird because even when you command it on, it doesn't turn on, not even the fan motor, but the lines change temp anyway. One gets warm, the other frosts up a bit.

All the relays and fuses are good btw. And it has the ACC system.
It's impossible for one line to warm up and the other frost up unless the compressor clutch is engaged. Low and high pressures remaining the same with the lines changing temp is also impossible. Time to re-examine the situation.

The compressor is of the variable displacement type so the length of the piston stroke within the compressor can vary. Perhaps they are stuck of improperly controlled so that the stroke is very short.
Thanks for your reply. I'm totally with you, man. I watched this thing, hut I never noticed it cycle on. Idk maybe it did briefly when I went into the cabin to check fuses, but I never heard any change. I guess it had to have.

What do you think though, could this pressure solenoid mess with the stroke of the piston(s)? I thought that was part of its function. Also, do you agree with the previous post that pressure equalizes when the system is sitting off for a while? I never knew it to do that, but I can definitely be wrong.

Thanks again guys.
The clutch does not cycle as often on a variable displacement compressor. It more or less stays engaged the entire time AC is selected. When there is less demand, the compressor reduces it's output by shortening the stroke length of the compressor. This a computer controlled system which anticipates demand and varies the position of the solenoid or spool valve within the compressor. The valve uses system refrigerant pressure within the pump/compressor to alter the angle of the swash plate, hence lengthening or shortening the stroke of the pistons. The solenoid/spool valve has been known fail. Unfortunately replacing this valve entails draining the system of all refrigerant.

It cannot be said what the problem is with your car until more diagnosis is performed. To properly diagnose the system a good scan tool and gauges are required and someone who knows how to use them.

Refrigerant travels in a continuous loop motivated to do so by the compressor/pump. Half way around this loop is a small orifice which restricts the flow of refrigerant but never totally blocks it. As the system sits inoperative, refrigerant gradually flows through the small hole [orifice] equalizing pressure throughout the system. Differential pressure between the high and low side only exists when the compressor is in operation, and for a small amount of time thereafter.

Usually the problem with an older car is the system has lost some of the refrigerant. If you can get the system operating and post what information you can, some one here might be able to help. Again, hot and cold pipes without compressor operation does not make sense. A re-test is needed.
Gotcha, thanks for the info. I remembered a little about this type of Compressor because I had one in my old Sonoma. Not exactly the same, but it was also variable displacement. I have a good set of guages and an "ok" scan tool. I do have hp tuners though. I wonder if the vcm scanner could help me. What sort of things can a better scan tool do to help with hvac? Sorry for my ignorance!

Yeah I watched a video on how to replace the solenoid and as much as I think that's the problem, I don't want to deplete/recharge his system without knowing for sure haha.

If yall have any more ideas, please feel free to throw in. I will do more research to see what the best way approach to this is. And thanks again for all the information!
Yes, you're right, I can't believe I forgot that!

It's a 2015 2.5L. It's got a few other issues too. For instance, the blower motor won't even start up. I only really got to look at it for 30 minutes because he had to go, so I still have to do some digging. But I did check fuses and relays. Simple stuff first. And the pressure in the system.
Copy, will do that when I see him next. That makes sense.
The blower doesn't work? A clue? The system is computer controlled. Part of the control is the HVAC panel which also controls the fan.
I would look at the power to this HVAC panel, fuses, connections. Fix the control of the fan first. Maybe connections at the body control module. This may be the entire problem.
Yes a good point, indeed. When he told me his heat was working either, it had me wondering.
1 - 7 of 13 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.