2000 Silverado AC Compressor cutting out

[Deereman]

My 2000 Silverado blows cold air until the engine is revved. When the vehicle is started it will blow cold air low side at 32psi 70* ambient temp, High side around 150. When I rev it up the high side will come up to around 200 psi and the compressor will kick out and won't start again until I shut the engine off and restart it. I have by passed the low pressure switch at the dryer, High Pressure switch at the compressor and the one leaving the condenser with no change.

[stu_pidasso]

32 and 150 pounds for 70F are normal. But 200 when you rev to the point it cuts out is not. Do not bypass the pressure switches, especially after you discovered the high side cranks out 200 pounds. Pressure switches are not a computer nanny. They are very, very necessary. If you need to bypass them as part of troubleshooting, only do it after you confirm the pressure ranges are normal. You run the risk of over pressuring parts of the system, blowing seals etc. 

 

Has any work been done to the AC like new gas or a gas top up? Does the condenser fan cycle and can the condenser get good air flow? Does the compressors clutch cycle properly? Or does it just engage and stay engaged? If it cycles properly, there is a chance theres a restriction somewhere. When the high side goes to 200, what happens to the low side pressure? 

[richard wysong]

Stu has good advice. it could also be a bad relay or weak compressor clutch. check the voltage and the ground at the compressor. a scan tool that does live data can tell you if the compressor is comanded on by the bcm

[DENALIA]

12 hours ago, stu_pidasso said:

32 and 150 pounds for 70F are normal. But 200 when you rev to the point it cuts out is not. Do not bypass the pressure switches, especially after you discovered the high side cranks out 200 pounds. Pressure switches are not a computer nanny. They are very, very necessary. If you need to bypass them as part of troubleshooting, only do it after you confirm the pressure ranges are normal. You run the risk of over pressuring parts of the system, blowing seals etc. 

 

Has any work been done to the AC like new gas or a gas top up? Does the condenser fan cycle and can the condenser get good air flow? Does the compressors clutch cycle properly? Or does it just engage and stay engaged? If it cycles properly, there is a chance theres a restriction somewhere. When the high side goes to 200, what happens to the low side pressure? 

My 2013 GMC Denali is doing the same thing. At 103* ambient temp my pressures are 40-45 on low side and 140-150 on high side. I just got it back from the shop and they said it did not have any r134 in it. He said the filled it with 2 cans r134 and the idle pressures are normal. While taking off from a stop you can feel the air cut off then once you maintain normal throttle pressure it gets cold again. 
 

any help will be appreciated. 

[richard wysong]

idle pressures normal but what about off idle? either the charge is still low or under hard acceleration it's normal for the ecm to shut the compressor off. this is why you recharge by weight not pressures

[Deereman]

I plugged back into it today at 70* ambient temp. Before starting the truck I had 72psi on the high and low side. Running I had 25 psi  low and 145 psi high. When I gave it throttle the low side dropped to around 22 and high side went to 160. After the idle came back the compressor kicked back in. Which it wasn't doing the other day. We did remove a bit of freon. 

[richard wysong]

you have a low charge now. time to start over, evacuate the system and charge with the correct freon weight, add a tracer dye in case you have a leak

[Deereman]

Will I need to add oil with the recharge, or does that stay in the system when it’s put under vacuum?

[txab]

No oil is lost during the vacuum process. Adding dye to the system at this time is a great idea.

 

 

[richard wysong]

you may lose some oil during evacuation. if you use a recovery machine it will capture and measure the recovered oil so it can be replenished. you may find a local garage that will do the recovery for free if you are doing the vacuum and recharge yourself. some recovery machines also weigh the recovered freon

[DENALIA]

On 7/4/2022 at 4:34 PM, richard wysong said:

idle pressures normal but what about off idle? either the charge is still low or under hard acceleration it's normal for the ecm to shut the compressor off. this is why you recharge by weight not pressures

Thanks for the info. Is there a tag somewhere in the engine compartment that says how many oz. should be put in?

[richard wysong]

yes, sometimes on top of the accumulator or rad support

[Deereman]

On mine the sticker is on the radiator support. I was planning to do the recovery myself with a vacuum pump and scale, and recover the Freon into a recovery can. I wouldn’t mind having some HVAC tools for future projects.

[richard wysong]

if you have a vacuum pump that will do that go for it. all the vacuum pumps I've owned vent to the atmosphere 

[richard wysong]

you can buy PAG oil with dye already in it, check service manual for viscosity.