HVAC control panel and engine fan issues, a little help over here please...

[mwilson]

My son recently purchased an '04 2500. Heater control had intermittent issues and has now given it up completely. He was all ready to order a new one but then noticed that the engine fan is not engaging......WTH...

Symptoms as follow...

Heater blower motor works fine.
Heater doors will move once in a while, then default to defrost
No A/C or Heated Mirror indicator light action
Engine fan not engaging at all.
No A/C operation (was working when purchased)
Fuses are fine unless he missed one somewhere.
Two codes present...

P0646. A/C Clutch Relay Circuit Loss

P0450. Cooling Fan Control Circuit Open

He has NOT checked the fan clutch wiring harness, I told him to do that tomorrow. Noted for issues as we all know.

So, can a bad control panel freak out the engine fan or can an engine fan issue freak out the control panel?

Any and all suggestions welcome and appreciated.

Mike.

 

[Prairie Dog]

Your fan has failed and it is corrupting or pulling down the bus.
Unplug the fan and see if everything else is ok. You'll probably need a new one, DONT BUY AFTERMARKET! Get an OEM (yes they are expensive but worth it) clutch or you will have even more problems.

The problem with the HVAC doors is probably a separate issue. It's a common problem for the blend doors to break - check out Heater Treater for a good fix.

 

[mwilson]

Thank you, we will unplug it tomorrow. We figured that the bus was being messed up, but were unsure what was the culprit. The heater door action may be a result of the control panel coming to life every once in a while.

We will post the results of the test tomorrow.

Mike.

 

[rscurtis]

My HVAC system would also work intermittently. What was happening is that the splines in the mode 1 door were stripped. As I understand it, the stepper motor will make one revolution, and then stop. When you restart the truck, it may work again if the splines happen to grab. The HT parts should fix it permanently.

 

[jhenderson]

I'm having the same heater control problem. Mine likes to default to vent. If I cycle to recirc, then heater and wait 15 seconds it comes around, then I can get defrost. I have done the heater treater swap while I had thing apart for evaporator replacement.it didn't help. My next move is the control panel.

 

[mwilson]

Well, he unplugged the fan harness last night and rebooted the truck. No change.

The fan clutch is weak, he can get it to freewheel 3 to 4 revs so it is on the way out.

Thinking he has two issues, fan and panel. He also mentioned the cluster acting up on occasion, kinda' have to drag this info out of him one tidbit at a time.....

Mike.

 

[mwilson]

I'm having the same heater control problem. Mine likes to default to vent. If I cycle to recirc, then heater and wait 15 seconds it comes around, then I can get defrost. I have done the heater treater swap while I had thing apart for evaporator replacement.it didn't help. My next move is the control panel.

Just talking to him, when it started this summer he had to rotate the knob all the way to Max A/C and back to defrost to get it off the panel and onto the windshield. Fine until you hit a bump and then back to panel it would go.
When the A/C light on the panel is on you can run the panel through the paces. If the A/C light goes out you have no control over anything other than the blower motor. Full heat out the panel vents, like it or not.
Suspect the circuit board in the panel.

 

[Prairie Dog]

The 06's had a lot of problems with poor solder joints in their gauge clusters. It would usually show up as a dead gauge. If that is what's happening then you can either rework the joints yourself (if your experienced) or have a shop do it.

 

[PWong]

According wiring diagram 8W-42-4 (2005) HVAC MICRO CONTROLLER which is part of the control panel is in the picture for most of your symptoms.