Author Topic: A/C - Heater Fan issue... (Read 11941 times)

mapandjlp · « **on:** January 09, 2010 - 09:57:26 PM »

My '70 Challenger heat / a/c blower only blows one speed and only when the a/c buttons are selected. It doesn't blow at all on heat functions. The fan speed switch makes no change. Any ideas on where I should start?

ShelbyDogg · « **Reply #1 on:** January 09, 2010 - 10:14:13 PM »

Check the plug in the middle of the A/C box. It has all the load resistance wires to give you the different fan speeds. Should be under the glove box, but facing towards the seat.

Slotts · « **Reply #2 on:** January 10, 2010 - 11:07:46 AM »

Sounds like you have a couple if issues going on at the same time. As far as the fan not working in the heat or defroster positions, try testing your vacuum switch. That is what will enable/disable the motor from working. All four positions should show continuity except the off position.

Slotts

mapandjlp · « **Reply #3 on:** January 10, 2010 - 11:55:32 AM »

Thanks for the input, Guys! I'll take a look at it next weekend and let you know how it goes.

mapandjlp · « **Reply #4 on:** February 17, 2010 - 06:23:05 PM »

I finally got around to checking out my blower issue. I checked the resistance at the switch, definitely have continuity in all positions but off. I removed the resistor and checked it out. Looks ok, resistance is about 2.4/2.9/3.4. I don't know if that's normal but seems logical to me. Any thoughts before I replace the resistor?

Slotts · « **Reply #5 on:** February 17, 2010 - 07:18:37 PM »

I am reading 2.2/3.0/4.2 so I don't think your resistor is the issue. Could you try measuring your heater fan switch and see if both low and high positions are working separately. It might be your switch not traveling internally far enough to hit the high fan position is and is still making contact on the slow speed.

Slotts

mapandjlp · « **Reply #6 on:** February 17, 2010 - 08:27:30 PM »

Thanks. How do I go about checking the switch?

Slotts · « **Reply #7 on:** February 18, 2010 - 08:22:25 AM »

The bottom middle pin will be your common. Test between that and the two upper blades. In the low position one of the with show continuity and the other off. The move the switch handle to the high position and the other spade should show continuity and the low off. Both individual positions when on should show zero ohms of resistance. Give it a try and let us know.

Slotts

mapandjlp · « **Reply #8 on:** February 18, 2010 - 04:36:08 PM »

With the switch to the high side, both upper pins show continuity. With the switch on the low side, neither of the upper pins show continuity. So, is it the switch?

ShelbyDogg · « **Reply #9 on:** February 18, 2010 - 05:39:06 PM »

Quote from: mapandjlp on February 18, 2010 - 04:36:08 PM

With the switch to the high side, both upper pins show continuity. With the switch on the low side, neither of the upper pins show continuity. So, is it the switch?

is the one speed it blows on, high speed? You can check it by hooking the battery straight to the motor's wire in the engine compartment.

I have 7 wiring harnesses spread out on my basement floor now, trying to build a good one for my vert. I'll power one up and see what exactly drives what. Answer the speed question for me........

Slotts · « **Reply #10 on:** February 18, 2010 - 07:39:51 PM »

Yes, with readings like that on your switch, it needs restored. I do that work if you would be interested. You can take a look under the company folder section to see my work.

Not a bad idea to do as a test sending some 12 vdc down the lines to test the motor. I think you should be ok since you tested the the vacuum switch and resistor plate.

Slotts

mapandjlp · « **Reply #11 on:** February 18, 2010 - 09:34:19 PM »

I took the switch apart, cleaned it, made an adjustment or two, and put it back together. Now it appears to be functioning properly. One position gives continuity on one pin, next position gives continuity on the other pin, final position gives no continuity. Still, nothing has changed. The fan only runs on high and only when the A/C functions are selected. Of course, I'm assuming it's high speed but it sure sounds like it's on high. Any thoughts on where to go from here?

Slotts · « **Reply #12 on:** February 18, 2010 - 10:23:39 PM »

Well the good news is it appears that the fan switch, vacuum switch and resistor plate has been tested and found to be of working order. So what�s left is wiring. There may be a melted wire between the low and high speed that would cause the pathway to run the motor on full in either fan position. There may be a swapped pair off wires in a socket. Do you have the wiring schematic from the service manual? I think verifying that the harness is not damaged and the wiring colors are in the correct socket positions. That will be a PITA because that harness is really buried but there is not much left to test.

Slotts

ShelbyDogg · « **Reply #13 on:** February 19, 2010 - 12:51:05 AM »

Here you go. It helps if you look at the wiring to the blower. There really isn't too much to this circuit so you shouldn't be having such a problem troubleshooting it once you see my diagram.

mapandjlp · « **Reply #14 on:** February 19, 2010 - 07:46:37 AM »

Thanks, Guys! You've been a HUGE help! I'll get back to this, hopefully this weekend. I'll let you know what I come up with.

One thing - I noticed that the two seperate wires going to the back of the vacuum switch aren't on your diagram. What are they for?