HVAC woes

365Jeep

365Jeep

Member
Joined
Jan 27, 2016
Messages
49
Location
Siloam Springs, AR
Been I while since the posted. I’ll have to update soon.

Here’s the situation. My heater fan stopped working. It has been temperamental in the past. I’m having a bit of trouble diagnosing, so I’ll list out the symptoms in the order I found them.

- Over the summer I tried charging the A/C, and I noticed the A/C clutch would not engage. No fuses blown. Hypothesized the A/C clutch was out, but I did not “fully” confirm.

- Weather cooled down. Temp control works. Vacuum control will change where the air vents.

- Fan will not blow, and fan switch does not work in any position.

- Today I disassembled the dash to diagnose. No fuses blown. When I use a circuit tester on the switch, all 5 wires have current. When unplugged, only one does.

- When I looked at the “master” controller with the on/off/AC switch, the middle wire (C1 12 DG maybe) was burned and disconnected. The wires adjacent showed signs of heat damage.

- Do I have a switch problem, a resistor problem, a blower motor problem, or an A/C clutch problem?

Please help. It’s a daily driver, and defrosting the windshield is becoming problematic.

David
 
What happens if you unplug the blower motor from behind the battery and run power to one wire and ground to another?

My AC clutch is out on my 97 and short of no AC I have zero issues with heat in any position including defrost. Got a new compressor in the other day...Jeep is running so well I'm afraid to touch it.

-Mac
 
365Jeep said:
Been I while since the posted. I’ll have to update soon.

Here’s the situation. My heater fan stopped working. It has been temperamental in the past. I’m having a bit of trouble diagnosing, so I’ll list out the symptoms in the order I found them.

- Over the summer I tried charging the A/C, and I noticed the A/C clutch would not engage. No fuses blown. Hypothesized the A/C clutch was out, but I did not “fully” confirm.

- Weather cooled down. Temp control works. Vacuum control will change where the air vents.

- Fan will not blow, and fan switch does not work in any position.

- Today I disassembled the dash to diagnose. No fuses blown. When I use a circuit tester on the switch, all 5 wires have current. When unplugged, only one does.

- When I looked at the “master” controller with the on/off/AC switch, the middle wire (C1 12 DG maybe) was burned and disconnected. The wires adjacent showed signs of heat damage.

- Do I have a switch problem, a resistor problem, a blower motor problem, or an A/C clutch problem?

Please help. It’s a daily driver, and defrosting the windshield is becoming problematic.

David
Click to expand...

Head over to the resource section and download your service manual to see if you can locate and identify the burned wire. Could easily be just a tired/dead fan motor that was drawing excessive amperage as it aged (not uncommon).
 
I would test the blower motor to see if it spins freely.
Check the Blower Motor Resistor and the wiring looking for signs of overheating.
Attached is a page from the Factory Service Manual wiring for the A/C and Blower motor.
Hope this assists you to troubleshoot your electrical problem.


IMG_9938.jpg
 
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Start by checking the 2 fuses at the top of the page.
Next take a jumper and ground the brown/tan wire at the blower switch. The fan should come on high blower if not check the blower motor and relay.
Next check the mode switch with an ohm meter you should have continuity from the dark green wire to the black wire in all positions except off.
It sounds like you have a blower motor drawing excessive current causing connector to melt. This would require blower motor, switch and connector. After this verify blower works in all positions if not look at resistor and blower speed switch.
When the fan is working then move on to the A/C
 
First, thanks to everyone who posted.

I had already checked both fuses, and they were good. I pulled the blower motor, and it turned smoothly. It seems to run fine on the bench, and the contacts and wires look undamaged.

I pulled the resistor pack, and it and it’s harness look good.

I’m still puzzled by the fact that all the wires in the switch will light the test light.
 
The reason you are getting power is the power flows through the fuse, through the relay, blower motor then through the resistor and one wire directly to the switch then he ground is feed from the body G202 up through the mode switch (must be on) then through the dark green wire to the fan switch. When you switch the fan switch to high it grounds the blower motor directly through the brown/tan wire, when you switch the fan switch to #3 the current flows through the blower motor through one resistor through the fan and mode switch to ground. You will show power at all the wires because the switch is ground switching and you lost your ground ( dark green wire and mode switch) I colored this diagram hope it simplifies it and gives you a better understanding.

468AEDF0-C68F-450A-A010-4D925D6B90F1.jpeg
 
Last edited:
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Okay, I’m narrowing this down. The dark green wire on the mode switch had burned through (and had a bit of green corrosion). I plugged the fan switch back into the harness and jumped the dark green and ground wires. The fan came on, and I could switch between all 4 settings. Even though the fan works, I suspect it’s drawing too much current. For safe measure, I’ll probably replace the panel as it’s only $60 on Amazon.

Any thoughts? Am I seeing this right?
 
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365Jeep said:
Okay, I’m narrowing this down. The dark green wire on the mode switch had burned through (and had a bit of green corrosion). I plugged the fan switch back into the harness and jumped the dark green and ground wires. The fan came on, and I could switch between all 4 settings. Even though the fan works, I suspect it’s drawing too much current. For safe measure, I’ll probably replace the panel as it’s only $60 on Amazon.

Any thoughts? Am I seeing this right?
Click to expand...

Sounds like you found your problem and I would replace the fan motor.
 
365Jeep said:
Okay, I’m narrowing this down. The dark green wire on the mode switch had burned through (and had a bit of green corrosion). I plugged the fan switch back into the harness and jumped the dark green and ground wires. The fan came on, and I could switch between all 4 settings. Even though the fan works, I suspect it’s drawing too much current. For safe measure, I’ll probably replace the panel as it’s only $60 on Amazon.

Any thoughts? Am I seeing this right?
Click to expand...
You are correct, I would also put in a blower motor and the harness connectors that are melted.
 
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