My '02 Dakota's heating/AC system seems to be going on the fritz. I noticed about a week ago that the blower fan was turning on randomly for turning off after about five seconds. It's probably been doing that for a while, I just haven't ntoiced it since this is the first time I've had to blow air through the vents (I usually have it to floor and defrost).

Anyways, for troubleshooting, I turned on the fan and activated the A/C (so the light was on. I turned off the fan (which turns off the A/C light but it comes back on if you turn on the fan again) for this test:

• When the fan turns on randomly, the A/C light stays off. If I manually operate the fan, the A/C light will come on normally
• I can also randomly hear the outside vent door motor open and closing the vent door. When this occurs, the A/C light will turn on as the vent door opens, and turn back off when the vent closes. This occurs seperatly from the fan turning on issue described above.

Following up with the second point above, the A/C light will blink randomly regardless what vent setting is selected, but the vent door will open and close only when the setting is on a fresh air mode. I took a video to show it:
http://www.youtube.com/watch?v=BHk_cgAQdn8[/URL]
Light blinks at ~0 seconds, ~11 seconds and ~31 seconds.

Looking at wiring diagrams and the FSM, would I be right in diagnosing this as a problem with the A/C heater control and that it needs to be replaced? Or could it be an issue with the relay?

 

Bump.. any suggestions? I'm looking the FSM and it looks like it might be the A/C heater control module, but I'm hoping for a second opinion before I dorp that kind of money....

 

That is too strange. A really wierd problem. I agree with you and I also think it could be in the control head, because if it were a problem in the HVAC housing the blend doors would either not work at all or they would not move in relation to the settings on the control head. If this was my truck I would remove the control head and check the operation of the selector **** and the fan **** with an ohm meter. The FSM should tell you how to check the switches. Then if that checked out OK, if I could I would try to find the 2 wires going to the snowflake button that turns on the AC. If you could locate those 2 wires and short them together, then you could check to see if the AC runs like it should. There is a possibility though that the snowflake button has more to its circuit than just 2 wires to make it work like an on-off switch. It could be there is circuitry in the control head itself that has gone haywire and that's why it cycles on and off like that.

I would test the operation of the compressor too, be sure it cycles on and off like it should. You can short the compressor switch to make it run constantly too, as a test. And before I spent the money for a new control head, and since this problem is so strange I would try to get a used control head from a junk yard first and see if it makes the AC work like it should.

I am no expert with AC but that is one of the wierdest things I have seen in a long time.

Jimmy

 

No kidding its an odd issue. I'm going to take a gamble and order a new control unit. It acts up only when the fan speed selector is off. When the fan is running, everything works (ie AC, blend doors, etc.)