I have a 1996 K1500 pickup with a 305 V8. Recently I have encountered a problem with the cooling system. I turn on the heat in the truck and the air is cool that comes out, meanwhile the temp gauge for the engine goes way up, the temp will then suddenly drop and the air blowing out of the vents becomes hot, then the air will cool back down and the engine temp will go way back up. It repeats this process endlessly. Meanwhile i will have the AC switch in the cab off and the AC compressor will kick on and off randomly. I have replaced the thermostat to the cooling system and it is still having the problems. Are these two issues related? If anyone has any ideas as to what could be wrong that would be great. Thanks

 

Its got to be low of coolant to get hot,then cold like that...let her cool off and make SURE its full.

the a/c..maybe a relay.

 

I added some more coolant last night that seems to be helping. As for the AC I took the relay cap off and it keeps switching on and off is that due to a bad relay, because it only does it when I turn on the vent fan switch if i leave the vent switch in the off position it does not do it, but as soon as i turn the vent fan on (not turning on the AC button) it starts turning the AC compressor on and off. Thanks for the help.

 

No..it wouldn't be a relay then...Maybe a control head...or (hope not) some wires melted together in the dash...

 

I will have to check out the control head and wires then. Hopefully the wires didnt melt, I havenot smelled any melting rubber or anything burning so hopefully I can get away with a new control head. Thanks for the help I will keep the post updated with any new finds.

 

What needs to be done is..
get a test lite...spend a FEW bucks on a decent one (not a dollar store one)...and begin at the back of the control head and "follow" the current...
A schematic would really help as well