Heater / AC blower fan motor going bad?

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timk225

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I shouldn't be surprised that a 52 year old motor might go bad, that seems to be what's happening.

Even from when I got my 1973 Duster back in the summer of '24, the heater / AC fan motor always worked well and blew air well. But a couple weeks ago it decided to quit.

In my troubleshooting, I ran a wire directly from the battery to the power lead of the motor (it is grounded through the case), and it ran well on high speed.

So I figured that either the on/off electrical switch in the AC controls or the low-med-high fan speed switch had an issue.

But once I got the heater / AC controls out of the dash, I saw problems. Looks like the low-med-high switch got hot, the plastic wiring plug is partly melted.

I had emailed thepartguy.com and he suggested the blower motor might be failing, causing high amp draw, and overheating the switch.

Anyone ever have this problem?

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I perscribe new switch and replacement harness connector, and a touch of dialectic goop.
Replacement screens are/were available if cosmetic matters.
 
That is a tough one. Look up the required fuse in the circuit, I mean what was specified, not what happens to be there. That is not sure fire, because those circuits are shared. Then measure amp draw of the motor. This MUST be with the heater installed, in place, etc, because the airflow through the blower affects current draw. I doubt there is a specif spec for amp draw, but that would give you an idea.

Many/ most/ all? of these are not grounded through the case. There should be a separate I think? brown wire with an eyelet, run over and bolted to ground.

Might be a combination of the two, a bad switch and a bad motor. Hard to say, I think. I do not disagree with Redfish.
 

Clogged coils kill HVAC blowers every day. Owners don't change filters regularly. Our a-body has no filters before coils. Not even the minimal window screen newer vehicles have.
 
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Common problem on 73-76 Abodies.
AC/heater wiring uses a separate harness that is not that difficult to replace.
Year one had many request for that harness so they had M & H start reproducing them many years ago.
You can clean and replace all the components but the switch can't handle the amps even with a new motor in the AC high blower position.
Certain wires in the AC harness should have been 12 gauge instead of 14 gauge.
Try to keep high blower speed usage at a minimum with stock wiring.

 
67Dart273 said:
That is a tough one. Look up the required fuse in the circuit, I mean what was specified, not what happens to be there. That is not sure fire, because those circuits are shared. Then measure amp draw of the motor. This MUST be with the heater installed, in place, etc, because the airflow through the blower affects current draw. I doubt there is a specif spec for amp draw, but that would give you an idea.

Many/ most/ all? of these are not grounded through the case. There should be a separate I think? brown wire with an eyelet, run over and bolted to ground.

Might be a combination of the two, a bad switch and a bad motor. Hard to say, I think. I do not disagree with Redfish.
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That might be right, a separate wire bolted to ground at the windshield wiper motor, I remember now. I had been running the blower motor on high a lot, the AC in the car isn't working yet.
 
I can't argue with anything above. They were meant to last 10 years. We're past that. If the heater core and/or vaporator core have never been cleaned or replaced, who knows what resides there today. Good luck
Edit, I have to address your running on high. The OEM heater should run you out of this car. I mean toast your biscuits warm. If you're running on high a lot, someting wong.
 
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I haven't been using it for the heater in summertime. I use it to blow air through the car since the AC isn't working yet. I disconnect the heater hoses in spring and summer to eliminate any excess heat getting into the car. I just loop the heater hose back on itself. I'll hook up the heater for winter time use, if it is even driven in the winter. I'm going to change the heater core anyway, who knows how old the one in there now is, and I'm not going to have it leaking on the new carpet. When I put carpet in the car.
 
RedFish said:
I perscribe new switch and replacement harness connector, and a touch of dialectic goop.
Replacement screens are/were available if cosmetic matters.
Click to expand...
I would like to change the labeled front panel, mine looks pretty bad. But the one I saw on thepartguy website has completely the wrong font on the letters, and I can't live with that. If anyone knows where to find an accurate reproduction, I'd probably get it.
 
townsend said:
Common problem on 73-76 Abodies.
AC/heater wiring uses a separate harness that is not that difficult to replace.
Year one had many request for that harness so they had M & H start reproducing them many years ago.
You can clean and replace all the components but the switch can't handle the amps even with a new motor in the AC high blower position.
Certain wires in the AC harness should have been 12 gauge instead of 14 gauge.
Try to keep high blower speed usage at a minimum with stock wiring.

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I had a heck of a time getting to the heater controls and getting them out. I'll have to look under the dash some more and see what's involved in changing that wiring harness. Does it run through the main bulkhead connector?
 
On 1973 Abodies the compressor and blower motor wires go thru the bulkhead connector.
 
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Correction has been made in post #12.
74-76 Abodies use a firewall grommet but the 73's run the wires thru the bulkhead.
 
timk225 said:
I would like to change the labeled front panel, mine looks pretty bad. But the one I saw on thepartguy website has completely the wrong font on the letters, and I can't live with that. If anyone knows where to find an accurate reproduction, I'd probably get it.
Click to expand...
Some mfgs dont bother to match fonts unless customer stipulates matching fonts. I have screens for eally amp gauges thst have been modified. Custom stocker shows volts scale. I would need to dig deep to find the vendor name again but you can mail your screen out to reproduced, die cut and all. Yeah I know it's don't a sticker. I've had items produced of this same material too. Affordable? In this case you are buying a 8x10 sheet of what ever count fits. Simply sell the surplus so in the end yours was free.
 
I took the fan assembly out and cleaned it up. Inside the AC evaporator area looked fairly clean. Once I got the fan off the motor shaft, I can tell the shaft is a little stiff to turn, the bearings are surely dried out. I didn't bring my tools in my car to work today (I have a lot of free time at work), so I can't try to take the motor apart until at least tonight and probably this weekend. I tried calling a few electric motor repair shops in my area, but they all either said they don't work on these little motors, or they are gone on vacation or just didn't answer.

I'm hoping a good cleaning and oiling of the motor is all that's needed. I'll check the brushes too.
 
Bearings are sintered bronze bushings. 3in1 may help a minute. In the the later models the fan would scrub the case long b4 melting its power source. I don't know about shims to stop that purrrrr noise. Yearone might have LOL
 
I finally got the motor apart today. Those stupid little recessed nuts that you can't easily get a socket or wrench on are a pain. I finally cracked one loose with a screwdriver and hammer. The other loosened without much trouble.

This motor is shot. Piles of rust powder, dirty, the fiber washer at the back was split in two.

Anyone know where I can find an exact replacement, to include the unique mounting system? Or a good used OEM motor?
 
1973 a/c blower motor part number is 3514305 which superseded to 3837343.
Chrysler shows blower motors from 73 and 74 Abodies will interchange.
Four Seasons has an aftermarket motor #35565 but they have modified it to fit 70-76 Abodies so it's not an exact replacement.
The original Chrysler numbers have become rare and expensive.
Maybe you can find a used one.
 
I can think about the entire cars I bought for a couple hun. Scraped remnants including that motor for 75. I also have to think those motors would be as bad or worse condition as your OE part. A used 50+ year old motor would not interest me.
If you research what other owners have chosen from aftermarket you can bet it will.be the most practical / affordable one. Good lick
 
townsend said:
1973 a/c blower motor part number is 3514305 which superseded to 3837343.
Chrysler shows blower motors from 73 and 74 Abodies will interchange.
Four Seasons has an aftermarket motor #35565 but they have modified it to fit 70-76 Abodies so it's not an exact replacement.
The original Chrysler numbers have become rare and expensive.
Maybe you can find a used one.
Click to expand...

If that Four Seasons one will bolt up to the firewall and fit right and work, then that's good enough for my needs. I don't care if it isn't 100% OEM original look, this isn't a show car. I can splice on the power connector from the original motor, unless I can get a new one of those plastic connectors somewhere.
 
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