Rear AC relay?
 

Hi folks,

After poking around for a bit, I was unable to find what I was looking for, so starting a new thread.

My Rear AC works for low and medium, but not high. Front AC works for Low, Medium, and (now) High - since I replaced the relay (see http://67-72chevytrucks.com/vboard/s...64&postcount=3 ). Folks on the forum helped me find it behind the glove box.

Anyone know if perhaps the rear AC also has a relay, possibly hidden somewhere equally fun? :lol:

Thanks,
-Greg/IrieReggaeMan

Re: Rear AC relay?
 

not many folks with rear air-conditioners, I'm guessing? I'm on my second rear-AC switch with the same behavior, so looking for other reasons why HIGH doesn't work.

Thanks!

Re: Rear AC relay?
 

I have a rear AC setup out in the barn I can look at but it is raining cats & dogs right now so it won't happen until it lets up some....

LockDoc

Re: Rear AC relay?
 

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There is both a relay and a resistor (on the same order as the heater resistor) on the inside of the rear housing. I'm betting one of those is the culprit. I would visibly check the resistor first to see if any of the coils are broken or touching each other......

LockDoc

Re: Rear AC relay?
 

Thanks LockDoc! I'll give that a check.

Re: Rear AC relay?
 

ok, so it took me a while to get back to this. Life gets in the way of non-essential old truck fixes.

Review: I'm trying to get my rear AC to run on high. Low and Medium settings work just fine.

I popped of the rear AC housing. I looked at the resistor, as suggested by LockDoc. A rough glance, I don't see any obvious failures. Here are a couple pics:
Attachment 1904164

Attachment 1904165

Attachment 1904166

Attachment 1904185

Attachment 1904186

and a short video:
https://youtu.be/PXq9Dhlf2ZY

The resistor has labeled INDAK 3929051. I see available resistors for sale labeled INDAK 3929055. I wonder if they are the same, or close enough.

Anyone have any ideas what to try next? Is my relay perhaps located somewhere else? Generally the relay should be near the thing it controls, so I would guess it's nearby. I didn't take apart the motor housing...perhaps it's in there?

Re: Rear AC relay?
 

Here is a copy from a post by Sneakysnake. It has the wiring diagram from a pickup A/C unit and I suspect the wiring on that and the Suburban rear are similar. The control switch sends power to the relay to control the med and low speeds and it should send power direct to the blower via the control relay. I don't believe that the relay should operate when high speed is selected thus the resistors are not part of the circuit at that time.
When the blower is turned from off to high the switch contacts from the high setting arc as the blower is not turning. Repeated over time this causes the high speed contact to fail. Having seen several units with toggle switches installed by POs probably means these switches are problematic and not available (or spendy)
Here is the link I copied the diagram from.

http://67-72chevytrucks.com/vboard/s...d.php?t=209480

To test your resistor use a meter set to ohms to check for continuity from tab #1 to #2 and then from tab #1 to #3 on the resistor. One ( the one with the larger coil) will have more resistance than the other. Then going from #2 to #3 will be total resistance of both checks (#1 to #2 and #1 to #3)

Good luck. If it continues to frustrate you try a post in the electric forum.

Re: Rear AC relay?
 

I will check mine for a relay since it is still apart.

LockDoc

Re: Rear AC relay?
 

thanks HO455 and LockDoc. I'll test out the resistance of the two coils. I'll see if I can trace the wiring from the resistors as well to possibly find the elusive relay. I have an all-inclusive manual 67-72 Haynes manual I'll look at too for inspiration.
At the moment I'm installing power locks from A1 Electric, and have the usual stumblings with running wires around the whole rig. Maybe I'll get lucky and run into the relay during that! ;)

Re: Rear AC relay?
 

"High" will never run through the resistor as the fan motor gets full 12 volts on high speed.

I don't remember a relay for the rear unit. That would mean all the power goes through the switch. Not good for the switch and probably should be on a relay