Heater blower motor resistor question

[68Timber]

My fan only works in the high position, so I was told it had to be the resistor. I took it out and it was corroded badly but not broken so I cleaned it up and checked continuity. It tested good between all poles so I put it back in. Still no joy. Then looking at the plug I noticed I'm missing a wire. What goes here - ground maybe? There is a corresponding pole on the resistor but I don't have a wire in that spot.

[motornut]

my 79 has other colours

[68Timber]

This is on my CUCV, so that may account for the color differences. You have the heavy duty resistor too, and have a wire in that spot of the plug. Looking at the back-side of the resistor, I don't see how it can work without one, but I posted the same pic and question on Steel Soldiers and another guy said his didn't have a wire there either. Thanks John. I'm going to try a new resistor and see if that fixes it.

[Matt Man]

Mine doesn't work on the lowest setting. I will follow along.

[motornut]

just thinking some fans are wired to be on low all the time,no off
I cut the brown wire at the speed switch,in both the 78 (fan 3 speed) and 79(fan 4 speed),
to have low as an "off",
maybe someone else had another idea to stop the fan?...pull out the wire?

[hatzie]

Originally Posted by BRUISER

This is on my CUCV, so that may account for the color differences. You have the heavy duty resistor too, and have a wire in that spot of the plug. Looking at the back-side of the resistor, I don't see how it can work without one, but I posted the same pic and question on Steel Soldiers and another guy said his didn't have a wire there either. Thanks John. I'm going to try a new resistor and see if that fixes it.

The CUCV electrical is similar to the civilian trucks but not the same...

You really need to download the DOD CUCV TMs from Steel Soldiers and the GM CUCV parts and illustration catalog.
http://www.steelsoldiers.com/....CUCV-TMs

52D_1984_87_CUCV_Parts_and_Illustration_Catalog.pdf

Double Orange wire is from HI switch and out to the fan. This one works.
Yellow is low.
Light Blue is Medium. This is Orange with a stripe faded to pink in your picture...

Are you getting 12v on the yellow wire with the fan on Low and the Ignition switched on?
Move the switch to Medium and check the LT Blue wire.

No volts= bad fan switch or wire.
Volts=bad resistor.

The CUCV GM parts book is in the manuals link or you can use the DOD parts manual TM92320-289-20P

The CUCV resistor is GM # 500890

[68Timber]

Thank you sir. I'll check those for voltage. I have those manuals and had looked but could not find it. I was looking in the -20, I'm not sure if I have the -20P.

[hatzie]

Originally Posted by BRUISER

Thank you sir. I'll check those for voltage. I have those manuals and had looked but could not find it. I was looking in the -20, I'm not sure if I have the -20P.

You need the translation from Army TM nomenclature to what's actually in them...
TM9-2320-289-20P is the UNIT MAINTENANCE REPAIR PARTS AND SPECIAL TOOLS LISTS (parts book)
TM9-2320-289-20 is the UNIT MAINTENANCE MANUAL (Service Manual) I got the wiring diagram from this one.

Understanding Army Manual Numbers

[wilkin250r]

I've had similar problems on multiple cars. The first time I encountered this problem, yes, it was the resistor pack. However, on my current squarebody the symptoms were the exact same but the problem was the contacts within the blower switch.

I was able to take the switch apart and clean the contacts, but with little clips and tiny springs, it's not a task for those with a faint heart (or poor eyesight )


Exact same symptoms, different problem. Just another reference for people searching this thread in the future.

[68Timber]

Originally Posted by wilkin250r

I've had similar problems on multiple cars. The first time I encountered this problem, yes, it was the resistor pack. However, on my current squarebody the symptoms were the exact same but the problem was the contacts within the blower switch.

I was able to take the switch apart and clean the contacts, but with little clips and tiny springs, it's not a task for those with a faint heart (or poor eyesight )


Exact same symptoms, different problem. Just another reference for people searching this thread in the future.

And it's also worth noting that you can remove the switch only from the housing and replace just it, if you have one or can find one in the junk yard. A repop from LMC was $79, I wanted to try one.

[68Timber]

Well, I got the LMC heater controls hooked up. The temp and vent controls don't feel so good with a cable hooked to them. Flimsy. Does not feel like it will last. That's speculation though, and I won't ever know. It's going back. The fan switch is bad out of the box. I hooked up the old one to be sure. Oh well. It's not like the post office is crowded this week. Fudge.

[tucsonjwt]

My symptom was intermittent no power at the fan switch for several years of fiddling with it. I finally got an LMC heater control assembly and it still did not fix the problem. I could wiggle the connector at the fan switch and it would work. The solution was to get a new short harness and connector to the heater control. I think you can find this harness in the AC Delco pigtail/harness catalog online. You might also find an AC Delco heater control online from the OEM suppliers - most likely cheaper than LMC.

When I was in college I worked for one summer in the Chevy parts plant that made these heater controls. One guy had a full time job fixing these things so the heater control levers would work - if they worked smoothly coming off the assembly line it was an exception. These were far from precision made components.

[68Timber]

Yeah, apparently they get hot inside the pigtail and melt at the connection and you can still buy the pigtail or the switch separately. I haven't been able to find the whole assembly anywhere but LMC. Out of the box, it seemed nice. The levers moved smoothly with positive detents. But once a little bit of tension was on them, they were crap. And I made sure not to hook those cables up in a twist, they were just like they came off. Oh well. I'll see if someone here has one. If you know of a supplier for AC Delco replacements I'd appreciate it.

[wilkin250r]

Good info. I was thinking about trying the LMC repop, but if it feels flimsy, I think I'll just stick with reconditioned original.

[hatzie]

If the switch is melting... You can use a 5 terminal 40A Mini ISO relay to limit the current through the switch when the blower is set on HI. The civilian AC equipped trucks did that with a proprietary relay.

Terminals;
Coil- 85- Chassis ground.
Coil+ 86- Orange 52A wire from switch HI
COM 30- Power Out to Blower
NC 87a-Orange 52B from resistor pack (Low & Med)
NO 87- 12v battery power through a fusible link (HI)

[68Timber]

Originally Posted by hatzie

If the switch is melting... You can use a 5 terminal 40A Mini ISO relay to limit the current through the switch when the blower is set on HI. The civilian AC equipped trucks did that with a proprietary relay.

Terminals;
Coil- 85- Chassis ground.
Coil+ 86- Orange 52A wire from switch HI
COM 30- Power Out to Blower
NC 87a-Orange 52B from resistor pack (Low & Med)
NO 87- 12v battery power through a fusible link (HI)

And mount this on the firewall behind the switch? I've used relays here and there but I still speak 12v haltingly - forgive my ignorance.

[hatzie]

Originally Posted by BRUISER

And mount this on the firewall behind the switch? I've used relays here and there but I still speak 12v haltingly - forgive my ignorance.

Mount it wherever it's out of the way. GM put the AC blower relay on the AC box in the engine bay. Just be sure the terminals are facing down so water will not fill the relay.
Autoshop101 Relays

[68Timber]

Originally Posted by hatzie

Mount it wherever it's out of the way. GM put the AC blower relay on the AC box in the engine bay. Just be sure the terminals are facing down so water will not fill the relay.
Autoshop101 Relays

I appreciate the help. From looking at the schematic and comparing it to this:

Terminals;
Coil- 85- Chassis ground.
Coil+ 86- Orange 52A wire from switch HI
COM 30- Power Out to Blower
NC 87a-Orange 52B from resistor pack (Low & Med)
NO 87- 12v battery power through a fusible link (HI)

it's starting to make sense. I think. Except for NO 87- 12v battery power through a fusible link (HI). Is that a wire you need to add, or can that come from the switched hot on the back of the fan speed plug? Whichever one that is, I'm not sure.

[68Timber]

I should have skipped the whole LMC controls and gone this route from the start. The cables clip onto the little control board behind the switch. I couldn't get mine to release, so I forced the issue and tore the tab. Why fight it, right? I have a new one sitting here from LMC. So now, instead of just getting a new switch for my old controls, I need another complete unit. Ebay to the rescue. These are the sellers pics.

[hatzie]

Originally Posted by BRUISER

I appreciate the help. From looking at the schematic and comparing it to this:

Terminals;
Coil- 85- Chassis ground.
Coil+ 86- Orange 52A wire from switch HI
COM 30- Power Out to Blower
NC 87a-Orange 52B from resistor pack (Low & Med)
NO 87- 12v battery power through a fusible link (HI)

it's starting to make sense. I think. Except for NO 87- 12v battery power through a fusible link (HI). Is that a wire you need to add, or can that come from the switched hot on the back of the fan speed plug? Whichever one that is, I'm not sure.

That one is a new wire. It offloads the current draw from the Blower switch with the blower on HI. GM did this with the AC trucks. Not sure why they didn't do it with the base Heater trucks.