Temp Contol Unit

RogerD · Posted: Tue Aug 12, 2008 4:31 pm Post subject: Temp Contol Unit

Can someone tell me how to know if my temp control head is bad? My ac compressor runs when on everthing but heat. I am not getting proper cooling (about 68*)and the compressor cycles off and on constantly. It has R12 in the system. The temp controle moves the door correctly and the selector switch moves around the vacuum line positions ok. Just started this problem all of a sudden last week. Anyone had this happen or may have suggestions on how to test the system?
Thanks, Roger
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1980 El Camino
1951 Chevy Styleline (in restro)

mhamilton · Posted: Tue Aug 12, 2008 8:28 pm Post subject:

I think you have two separate issues to deal with. The easier of the two is probably the control panel.

The compressor clutch should receive 12v (through the low pressure cycling switch) from the control panel only in the 3 a/c positions and the defrost position. This is controlled by an electric switch that moves with the mode lever. It's a cheap part, should be available from any auto parts store.

The poor cooling and rapid cycling indicates a low charge. Look for leaks around connections, indicated by dirty, oily spots. You could top the system off and charge by pressures, but it would be best to recover and charge the system by weight.

Hope this helps,
-Michael

RogerD · Posted: Sat Aug 16, 2008 11:51 am Post subject: Temp control head

Well, after finally figuring out how to remove the ac heat control unit, found lots of grease, dirty connections, and burnt contact points. Glad I took it apart and found these problems, but now have to buy both switches including the fan switch. All had at some time arced over and one area had even melted some of the plastic. I did break the plastic fan switch shaft off trying to get the knob off. Anyone know how to remove them without breaking the levers? Know I have to figure out how to get the broken peice of lever out of the knob, or where to buy another knob.
Thanks for the ideas, and hope this might help others with same type problems.
Roger
_________________
1980 El Camino
1951 Chevy Styleline (in restro)

mhamilton · Posted: Sat Aug 16, 2008 8:28 pm Post subject:

Had that happen with my fan switch. You have to be careful to pull the knobs straight off. To get the broken one out, I just worked it out with the tip of a razor blade and various small needle-nose pliers.