Heater Fan Control Switch Question

[robfg67]

My ’89 Comanche heat fan control switch operates in the high position only. I picked-up a new switch control at the local dealership today, installed it, and there was no difference. The 4-wire plug has no visual problems. Not sure if this matters, but the control assembly does NOT have AC.

 

What would be the next troubleshooting steps?

[Eagle]

Ther fan speeds are controlled by routing the circuit through a set of resistors with different ratings. Full speed doesn't go through a resistor. The lower speeds do. More than likely your resistor pack is burned out, so the lower speeds aren't sending any juice to the fan.

[HOrnbrod]

My ’89 Comanche heat fan control switch operates in the high position only. I picked-up a new switch control at the local dealership today, installed it, and there was no difference. The 4-wire plug has no visual problems. Not sure if this matters, but the control assembly does NOT have AC.

 

What would be the next troubleshooting steps?

 

If the fan operates only on the HIGH position, the blower motor resistor is most likely shot. Common problem, it's in the blower housing. P/N 56000522.

[comancheon33]

Very easy to do. It is behind a small cover on the passenger side just below the dash. Move the cover, remove the two screws and and unplug the old one. Reverse the process to get your multi speeds back.

[HOrnbrod]

My ’89 Comanche heat fan control switch operates in the high position only. I picked-up a new switch control at the local dealership today, installed it, and there was no difference. The 4-wire plug has no visual problems. Not sure if this matters, but the control assembly does NOT have AC.

 

What would be the next troubleshooting steps?

 

You should have asked your question before you shelled out the $$ for the new HVAC dash control switch. :oops: :oops:

 

But that's how I always learn too - the hard way.........

[robfg67]

I agree hornbrod-replacing the switch seamed so obvious and it was only $12.

 

Does anyone know how much the blower motor resistor costs? Is this a part that can be purchased from NAPA or is it a dealer part only?

[HOrnbrod]

I show it from the dealer at about $7 and change.

[HOrnbrod]

Oh, and pull yout old one first, will be obvious if it's smoked. You might even luck out and find a wire lose or disconnected.

[robfg67]

Ok, I took the 2 screws off the black roundish cover just below the dash on the passenger side and there was an electrical connector attached to a cardboard-type cover that also had 2 screws holding it in place.

 

As you can see from the pictures below, the connectors are fully rusted and one of them is actually rusted into two pieces. Is this the blower resistor?

 

Do you think I can file/de-rust this part in order to get it to work again?

 

 

 

 

 

[HOrnbrod]

Yes, you are there. Dayem, that looks terrible. :oops: :eek: Get a new resistor pack from the dealer - it's cheap and clean up the harness plug and you should be good to go. Use some dielectric grease when reassembling. Is all that rust possibly from just weather/age or a leaking heater core?

[robfg67]

Thanks again hornbrod!

 

I'm pretty sure it's just from age. There are no signs of leakage inside the housing. By the look of this piece, I'm lucky to have heat at all!

[HOrnbrod]

The blower control speed control resistor module burning up is a common problem. The AMC engineers designed a fail-safe circuit to allow bypassing the voltage dropping speed control resistor pack if it smokes, but under-designed the power rating of the wire-wound resistors, especially if the blower motor gets stuck and sucks up amps. The resistors blow most often before the fuse blows! Anyhow, let us know if a new pack fixes it. A new splice-in connector is also available from the dealer and aftermarket sources if yours is beyond repair.

[robfg67]

If I were to destroy the connector head during the disassembly & removal, would I still have the high fan setting & heat? It is cold up here in the northeast. If so, I will purchase the splice-in connector at the same time to be on the safe side.

 

Also, are you or have you ever been a Jeep mechanic/engineer-your knowledge of the Comanche is insane!

[HOrnbrod]

If I were to destroy the connector head during the disassembly & removal, would I still have the high fan setting & heat? It is cold up here in the northeast. If so, I will purchase the splice-in connector at the same time to be on the safe side.

 

Also, are you or have you ever been a Jeep mechanic/engineer-your knowledge of the Comanche is insane!

 

When your HVAC blower switch is in the HIGH position, you bypass the resistor speed control pack. You can disconnect the resistor pack, and you will still have a functioning HIGH speed blower. But I would get the connector also, because when you pull it apart it will prolly disintegrate.

 

And no, just a redneck electrical engineer in my past life in the federal gov before I recently retired, have some good sources, have all current FSMs (your best friends), and have had lots of Jeeps. Mechanically; well that's a different story. There are true wizards in this forum in all areas, and most all are willing and very able to help each other.