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92 c2500 heater control problems


broughy84
01-10-2014, 04:03 PM
I have a 92 c2500 cheyenne. It's just a base model nothing special work truck with a 4.3 and 198k on it. The problem started yesterday after I replace a battery that the cold weather zapped.

Let me start out by saying the heater controls function fine. When I reconnected the battery, immediately my a/c clutch engaged. I started the truck and turn the heat/ac panel off and it disengaged. Not trusting it, I unplugged it, as I need my truck to start in the mornings to go to work! So I drive to the store last night and shut the truck off and the heat controls stay on as does the blower fan! I reached over and hit the power button and the fan and display went off. I didn't think a bunch about it.

Tonight on the way home from work it did it again. I drove around town then shut the truck off and it did it again. SO I pushed another button to see if it would switch vents and it shut off. I'm puzzled!

Has anyone ever had anything like this happen to them? I AM BAFFLED!!!

777stickman
01-10-2014, 05:43 PM
Try disconnecting the NEG batt cable for 15-30 mins. Just a thought.

Schurkey
01-11-2014, 12:57 AM
If the heater control in the dash is anything like the one in my '88 K1500, they seem to be cold-sensitive.

When I bought the truck, the heater control was so goofy I pulled it apart, and re-soldered the main connections. Many had cracked, they conducted intermittently. Re-flowing the solder made the system much more reliable.

When the ambient temperature is below freezing, I often have to push on the display to get it to light up and function. Yet another cracked solder connection, I suppose.

broughy84
01-11-2014, 12:25 PM
A little more information on this issue. This only seems to happen if I have the defroster on ( or the a/c ). I'm assuming since the air conditioning compressor is activating as soon as a connect the battery, my issue is a relay issue and it's back feeding power to the control cluster. SO, does anyone know where the a/c relay on this is?

broughy84
01-11-2014, 01:43 PM
Found the issue. Checked for voltage at the relay behind the glove box. Terminal 87 ( going out to the ac system) had 12 V on it. So did the pressure switch on the condenser. So I tracked it in between the two. There is a 3 conductor plug in under the dash ( Red, Dk Grn. and Grn) This had melted between the red and the light green connector. Cut the connector out, wired it together and all is well. Thank you all for the help.

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