I have a 2000 C5 and noticed recently that the A/C went from ice cold to cold on one side and cool on the other, and finally just ambient temp. It seems to have a full charge of 134,.which surprised me. When I vacuumed the system out last year, and put the recommended 26-28oz of 134 in, it worked great. Until now. I have my own vacuum pump and manifold gauges. So I vacuumed the system again, and it held a vacuum overnight. Now I see the compressor clutch is not engaging at all. I checked fuse #24, and it's good. I swapped the fuel pump relay out with the A/C relay, since they're the same relay. Since the fuel pump still works, the relay is O.K.. But of course the compressor clutch still won't engage. I also replaced the orifice near the dryer. I have the electronic climate control, and the light comes on when the A/C button is pressed, but goes out in maybe 3 seconds. All other HVAC functions seem O.K.. Air comes out wherever it's supposed to. Anyone have any ideas? Any help would be greatly appreciated. Thank you.

 

Any codes?

 

No codes......

 

Do you know anyone with a GM Tech II?
There may be something shut down in the BCM or a bad sensor somewhere.

 

I.d put power to the clutch and verify its locking. (probably is but its an easy thing to rule out)

 

^Agree

 

FIRST see what your low side reads after the car has been sitting for a while when you hook up the gauge set...low side pressure should read close to the outside air temp...have you checked this recently since the AC hasn’t been working ??...if good I’d remove the relay and jump pins 87 and 30 (pictured) at the fusebox. The terminal numbers are on the bottom of the relay but they normally sit diagonally across from each other...first I’d see if you have power at 87 and 30 is the ground G102 which goes into the splice pack 100 which is behind the R/H headlight....if that doesn’t work you’ll have to check for power down to the compressor or if you have a bad ground...if jumping 87 and 30 engages the AC clutch with key ON...you will hear it click !!...you should see if you have power at pin 86 or 85 at the relay...can’t remember which one but you’ll always have 2 terminals at a relay that should have power when the key is ON. Also you may have issues with the AC pressure sensor which sits aft of the high side Schader valve....just back probe the signal wire (red/black)...you can stick a safety pin into the back of the connector....you should have 1 volt with AC off at idle and 2.8-2.9 with AC on !!...if the clutch is engaged see what our high side reads...290 psi is good...if 290 psi with compressor running but have 1 volt our pressure sensor is bad !!...if you were to disconnect this sensor you would have the AC light come on for 3 seconds and go out !!

 

I wish I did, but no.

 

Clutch is not working at all. I know generally speaking when refrigerant is low, a clutch will try to cycle for a second or two, then disengage. Mine is not even doing that, not clicking, nothing. When in the drivers seat I can select the gauges function, go to battery volts, and when checking that the voltage doesn't change at all. When all is well, you can usually hear the clutch engage with a click, and engine rpm momentarily drops slightly. Mine shows no voltage drop, no engine RPM drop, and when viewing the compressor clutch you never see it spin. The belt is on. I think something is preventing it from getting any electrical signal. Relay is good. Fuse is good. I'm stumped....

 

Don’t be stumped...it’s not a difficult circuit to diagnose !!Like I said jump pins 87 and 30 with key ON and see if clutch engages...this is the LOAD side of the relay...if not you MUST check for power at the clutch and also that your ground is good !!

 

Haven't checked voltage yet, but I have confirmed relay and fuse #24 are both good. You're correct about low side pressure; It was near 0, and after pulling vacuum I was able to get maybe 1/3 of 12oz can into it, but can just got cold because the compressor clutch won't engage. Thank you all for input. Still frustrated, but guys on this forum are the BEST!! I'll check pins when I get home this afternoon. Thx again!!

 

What is puzzling is how it gradually stopped cooling. Almost like a slow refrigerant leak. But it held vacuum overnight. On the other hand, vacuum has a LOT less suction than the compressor has pressure on A/C system. Might be a couple things. I'm thinking the compressor may be going, or already gone, and something in the electrics has dumped. After all, EVERYTHING is 20 years old, and original.......

 

Checking the high side of the refrigerant would tell you if the compressor has worn out.

The orifice tube may be clogged.

 

Your were just LOW on refrigerant !!...I think 24 oz is the correct amount !!...if your clutch is now engaging and AC working just check your low and high sides...I’d see if you may have a slow leak !!

 

Let me just suggest that when you jump the relay to force the clutch to engage for troubleshooting purposes, don't run the compressor without connecting your A/C gauges first. You want to keep an eye on both pressures at all time. It might be that your High Pressure Switch or your Low Pressure Switch is being activated to protect your system.

 

You are absolutely 100% correct about not running the compressor without sufficient refrigerant... I believe there are no high and low pressure “switches” that I know of...there is however an AC refrigerant pressure “sensor” (3 wires with a 5 volt reference)...it reads the high side pressure and this can be seen on a scan tool or you can back probe the signal wire...1 volt at idle AC off and 2.8-2.9 volts with AC on....2.9 volts is about 290 psi. If pressure drops below 30 psi compressor will not engage..,Let me know...thanks !!

 

True... Brain fart! Anyways, the idea behind my suggestion was to prevent damage to the compressor due to either low pressure below safe threshold, or extremely high pressure, when temporarily bypassing protections during troubleshooting. I still recommend monitoring both pressures while jumping the relay. One can never be too careful!

 

Moved to C5 Tech.

 

Thanks all. Family life got in way of C5 life this weekend. As for being low on refrigerant, I realize its low, but it wont take anymore from the refill can when I try because compressor never engages. Several of you guys know more about this than I do. Just because I have a set of gages and a refrigerant "sniffer" doesnt make me an expert! Thanks much for the help. I do believe that the compressor is not getting any electrical signal. Does anyone know if the electrical connector at the compressor is accessible from the passenger side wheel well if that tire is removed? I DONT want to pull the rack! AGAIN!! I did have a major oil leak, caused by a bad compression fitting, that did oil most everything in the front and sides of the engine. However, nothing else was effected (yet!), if this is the root cause. I'm starting to think whatever sends the signal to the compressor isn't doing its job. I have the electronic climate control, and everything else, like blowing air in right places, high and low temperatures, work good.

 

I suggest you verify things first, beginning with the easy stuff, to avoid the pain and suffering that comes with unnecessary complications.

Why don't you jump the relay as suggested above, just with the key in the ON position and engine OFF, to verify if the compressor clutch engages or not? It's easier than even thinking of pulling the rack

If the clutch engages when you jump the relay, then whatever is happening, is happening in the control side of it. If it doesn't, THEN check the connector.

If you decide to check the refrigerant pressures, I suggest you connect your gauges first and then start the car and jump the relay. Since you are temporarily bypassing protections, you want to be able to keep an eye on both pressures at all times to avoid any potential damage.