Chevy p/u Air Conditioning Problem

[tonystewart01]

Just purchased a 1992 CK1500 v-8 and the air conditioner quit cooling on the way home while driving at highway speeds. I turned of the a/c for about 2-3 minutes and turned it back on. It began cooling again. After another 5 minutes or so it quit cooling again. I drove it the rest of the way home (about 5 more minutes) and couldn't get the unit to cool. When I got home, I opened the hood and the compressor wasn't running. I turned off the truck and came back in about thirty minutes, cranked the truck up and the a/c worked fine. Low refrigerant problem? Switch? Any ideas would be helpful.

[ChevyTech007]

Replace the cycling switch on the accumulator. Make sure the terminals in the connector are not spread apart and not making good contact with the pins in the switch.

[KICK]

Just purchased a 1992 CK1500 v-8 and the air conditioner quit cooling on the way home while driving at highway speeds. I turned of the a/c for about 2-3 minutes and turned it back on. It began cooling again. After another 5 minutes or so it quit cooling again. I drove it the rest of the way home (about 5 more minutes) and couldn't get the unit to cool. When I got home, I opened the hood and the compressor wasn't running. I turned off the truck and came back in about thirty minutes, cranked the truck up and the a/c worked fine. Low refrigerant problem? Switch? Any ideas would be helpful.

 

<{POST_SNAPBACK}>

 

 

 

 

you need to put gages on it and see if it is cycling out on the low or high side and go from there. .

 

it is normal for it to cycle, but not to stay off for long periods of time which indicates a pressure problem in the refrigerant.

 

92 still had R 12, dont know if yours has been converted to R 134a but it is quite possible it is low on refrigerant which will cause the condition you describe.

[tonystewart01]

It's been converted to R134A. I plan on picking up some manifold gauges today (mine only work w/ r12 fittings) to check pressures. Roughly what should I expect on low and high sides w/ R134A in 90-95 degree weather? At what pressure should the accumulator switch shut out? Thanks.

[tonystewart01]

OK... have quite a bit more info. I put the manifold gauges on today. It was 96 degrees out and the low side reading dipped to 27 psi while the low side climbed to 290 psi. Just before the compressor kicked off, the low side dipped to approximately 25 psi and the high to 270 psi. This was with the truck running at 1500 rpms with the windows down on recirculate at max fan speed. After several minutes (say 10), I rolled up the windows to get the compressor to kick off (this is the point at which the pressures began to drop slightly). The compressor then kicked off and never came back on even though the cab temperatures continued to climb. I'd say I ran the truck another 10 minutes and the compressor never came back on.

 

Additionally, I tested the cycling switch on the accumulator and it seems to work. Continuity exists when the compressor is running... and when it is "supposed" to be running but is not. I then went to the two pin connector mounted on the upper front of the compressor. While the compressor was running, their would be 12VDC across the terminals. When the compressor kicked off, the voltage would drop to zero. However, the voltage would cycle back on (12V) shortly after the compressor kicked off, but the compressor would not cycle back on. Repeated pressing of the A/C button would also cycle the 12V at the compressor on and off, but the compressor would not kick in. It seems to me that the 12V at the compressor should be signaling the clutch to engage but it is not for some reason. Could this indicate a bad clutch? BTW when I say the compressor does not cycle back on, I mean it makes no attempt to come back on... no chattering clutch, no momentary engagement... nothing. Thanks in advance for any suggestions.

[tonystewart01]

... Forgot to mention... at 96 degrees (ambient temp) the system equalizes to about 85 psi once the a/c is shut down. Don't know if it's of any use but trying to be as thorough as possible. Thanks again.

[pm26]

Check the A/C compressor clutch for resistance, If the circuit is open, the clutch coil is burned out.

 

On my 83 Mercedes 300SD, bad A/C thermostat switch caused the compressor clutch not to operate. I am not sure if the set up on Silverado is the same, but it is worth looking into. You can bypass the thermostat switch and see if the A/C clutch engages.

[KICK]

sounds like its cutting out on the hi side. I don't know the specs for the condesner pressure switch but I believe 270 is too high for a R12 system. it has been switched over to R134a but it still has the old switch I'd suspect.

 

 

 

you might have a clogged orfice tube, that will cause hi head pressure and low suction pressure at the same time.

 

see if you can get it to work and touch the condenser at its inlet, if its hot enough to burn you suspect the orfice tube.

 

pop the grill, discharge the system and remove the line going from the condenser to the evap, the orfice tube is usally in the condenser at that fitting.

[KICK]

http://www.ackits.com/index.cfm?fuseaction=Chart

[tonystewart01]

Thanks guys. Simultaneous posting to an a/c forum has diagnosed the problem. The air gap on the compressor clutch is too large causing the clutch to fail to engage. The lightest of taps on the front of the clutch will close the gap enough to allow it to engage. It appears that this gap is adjustable on at least some models so I'm waiting to find out whether mine can be adjusted. I'll post when I know for anyone else who may follow this thread. Thanks all.

[tonystewart01]

Here's the reply I got on adjusting the air gap. Thanks again to everyone.

 

"It can be adjusted. You can borrow the tools from autozone. You need the clutch plate "installer" to close the gap. Screws onto the center bolt on the shaft, then pushes the hub closer. Be careful, if you go to far, you'll need the clutch plate removal tool to pull it back out...press fit...

 

Push it in slowly until a business card is snug all around it, without the outer hub touching the pulley."