It's my 2000 4 door 4x4 with 224k miles. The A/C blows cold when the temp dial is turned to cold, but it also blows cold when turned to heat. Actually, it blows cold compressed air through the heater core. I can tell it's doing this because it's a mixture of hot and cold air. I've been trying to use the heat and was noticing the compressor kicking on even though the "AC" light/button is off and the temp's turned all the way to hot. I unplugged the compressor to keep it off and the heat got much hotter.

It's also been occasionally switching from bi-level vents to floor, back and forth. I am familiar with the vacuum lines, actuators, flaps, ducting and stuff, I've had that all apart before because I replaced the heater core. I'm pretty sure the flaps are all moving correctly, just kind of by their own will.

Please help!

 

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Auto-climate?
Is the fan speed varying too?
I never had the problem, and I sure's hell dont know how you would check the Control system. My response would be to double check all connections, then go to junkyard for a control module.

 

If the compressor is coming on when it's not supposed to, my guess would be the HVAC control module in the dash is bad.

For the vent issues, when the flaps move at will, it's a vacuum issue. Probably a leak somewhere, and the only foolproof way to track it down is to get a MityVac (or similar) and test each vacuum line and each actuator. If you take a look at the HVAC schematic here (scroll down to the bottom), it's a good reference for what's going on (or supposed to be going on) inside the dash.

 

Thanks for the help guys. I'll check into these things and see what I find. The fan speed does not vary at all, it stays where I put it. It might take me a little while to acquire a good tool for checking the vacuum lines for leaks, but once I do, I'll post the results.

Thanks again!