hvac is not allowing me to have cool air.

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Blackjack
Posts: 27
Joined: Sun Dec 26, 2021 3:36 pm

hvac is not allowing me to have cool air.

Post by Blackjack »

I got 2015 l77. It was sorta cool (a/c wise) when I got it, but it got less and less so until it was ambient temp. I looked under the hood and saw the hose assembly was leaking and showing green die on the rubber part. I replaced the hose and charged it. Compressor would not engage the clutch. Pulled the relay and forced it on with a power probe. Clutch engaged but no cool air or sweating hoses. Hooked up gauges and there is no pressure change on either side with clutch running. So, I stupidly replaced the (expensive) compressor. Same boat as before. Next I'm going to test the HVAC module wires for signal values. Spent too much already, now I need to think my way into fixing it. Any help would much appreciated. I have fixed a bunch of normal stupid systems, but this one is so smart, it's out-smarting me. Please someone have a solution! Thanks.
JoeR
Posts: 150
Joined: Wed May 25, 2022 12:34 am
Location: Central, NC

Re: hvac is not allowing me to have cool air.

Post by JoeR »

I can only imagine 3 reasons for no pressure change with the compressor running.
1) The compressor isn't pumping
2) The expansion valve is stuck completely open.
3) There's no refrigerant in the system.

Joe
Sanford
Posts: 356
Joined: Mon Dec 12, 2016 9:38 pm
Location: Texas Gulf Coast

Re: hvac is not allowing me to have cool air.

Post by Sanford »

The compressor is a variable displacement compressor. I believe the solenoid that controls the swash plate is pulse width modulated by the HVAC module. I have hooked a decent scan tool on the 11-13’s and I have not found any info as to the percentage the solenoid is on. May need a couple grand scanner to get that info or maybe a scope. Just be careful when running it. I had one on an 11 that locked up due to it not pumping. It lost the flow of refrigerant, which carries the oil with it. The swash plate and the buttons were torn up, put the pistons and cylinders looked like new.
Blackjack
Posts: 27
Joined: Sun Dec 26, 2021 3:36 pm

Re: hvac is not allowing me to have cool air.

Post by Blackjack »

Thanks everybody. I'm only running it (forcing the clutch) long enough to see if there's pressure changes. I have access to a few scanners at work, including a tech2 and some snapon verus and other types. I only get to use them on my 15 minute breaks. I'm thinking maybe the head unit is bad. I have to correctly guess which scanner will let me know if the switching is working.
Blackjack
Posts: 27
Joined: Sun Dec 26, 2021 3:36 pm

Re: hvac is not allowing me to have cool air.

Post by Blackjack »

BTW, I considered installing a new expansion valve. The basic scanners show no codes, and the old systems would have identical pressures because of a stuck expansion valve. It's the smart aspect that's slowing my roll on that. That, and all the goddamn money I've already poured down an open hole. I'm gonna see what the scanner tells me tomorrow at work and go from there.
JoeR
Posts: 150
Joined: Wed May 25, 2022 12:34 am
Location: Central, NC

Re: hvac is not allowing me to have cool air.

Post by JoeR »

The Snap-on scanners can do it, and of course so can the Tech 2.
To engage the Compressor Clutch: Engine/Functional Tests/Output Controls/AC Compressor Clutch Relay
To shift the variable displacement solenoid: HVAC (not HVAC Controls)/Functional Tests/AC Compressor Solenoid Valve

The Compressor Clutch may need to be cycled with the engine not running, but you can try it either way.

You're going to need the scope of the Verus to see if the HVAC Module is trying to shift the compressor plate. I'm betting you can use the 14V scale and 100mS sweep speed to see it.

Joe
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