Need troubleshooting help with aux. heater blower

[Leland Pate]

Ok, please don't get fed up with my wiring woes, but I's gots another one fer you "current flow" fans.

I'm running into the same problem I had several weeks ago with my power windows... only this time it is my heater blower relay that is popping.

Ok, first of all... someone please tell me what kinds of things can cause a relay to pop. No fuses,... just relays.
I can't afford to get into another $80 worth of relays blown situation.

With this problem I've already ruined 2. So, I come to the board for help.

On page 970-20 in the SC Bentley manual there is a good diagram of the heater circuit.

This is a pretty simple circuit, and I've checked everything I know how, and I'm still stumped.

Here's what I've checked so far:

Resistance is good between the following wires-
Red/white wire from fuse #23 to terminal #30 of the relay socket.

From #87 to the connector on the blower motor.

Red/Black wire from fuse #22 to terminal #86 of the relay socket.

I know power is flowing through wire #50 (yellow) to the starter solenoid, but I'm not getting any power from either of the yellow connectors on the heater handles (between seats) even when the car is running.

But there is no resistance between socket #85 and the 14 pin connector in the engine compartment.

Can I pull the blower motor out and put 12V on it to test it?



Also on a side note, when we looked at the small tabs that close the switches under the heater handles, there was some goo on one of them... possibly from a spilled soft drink.

Could this have been the culprit?

What steps should I take now?

[marcesq]

Leland:

You probably know this already, a relay is a switch that allows one side to handle high amperage when a switch that can not handle alot of amps is used to operate the item that draws the high amps. A relay can be damaged if the low amp side recieves high amps.

If the blower motor is bad or going bad it will pull more amps than if in good shape. You can and should pull the plug on the motor and straight wire the thing to see if it running smoothly. You can use the hot terminals on the rear fuse box for the test.

The micro switches between the seat should be cleaned, but they should not produce any problem except if they don't close. In that event the fan would not run at all.

[Leland Pate]

Thanks for the reply, Marc.


I'm going to do what you suggest, pull the blower motor and clean the micro switches some more.

One thing though,

Am I supposed to get power out of the two yellow wires that lead to the microswitches on the heater levers?

I couldn't get any out of them the other night.



Thanks,

[marcesq]

Ok . . .here we go.

One end of the yellow wire goes to the 85 pin of the relay. This pin should have 12v with the key in the on or start position. If you don't have power at the 85 pin start back tracking.

The other end goes to the 50 terminal on the starter, but you know this.

You should have 12v on the 30 pin at all times, or at the very least when the key is on.

You should have 12v on the 86 pin when the key is on.

With key off, Pin 87 should read 0 ohms when grounded.

See if this helps, and let me know what readings you pull and we can work from there.

[Leland Pate]

Marc,


I have:

12V @ #30 at all times.

12V to #86 when ignition is on.

And 0 ohms of resistance between #87 and the leads to the motor. I'm not sure what you meant by "ground".

It appears that my problem is coming from #85.

I was not able to get any power coming out of that socket.

So, now it is becoming apparant where the problem is... but I still can't see WHY this is causing my relays to pop as soon as I start the car!

I'm going ot have to look at the factory diagram again to see where this yellow wire comes from.

Thanks for your help.

[Doug Zielke]

Originally posted by marcesq
A relay can be damaged if the low amp side recieves high amps.

Not sure what is meant by that.

A relay is a set of contacts that are connected to an armature of sorts. A coil inside the relay is energized and attracts the armature/contacts, making the circuit complete.

Lee,
When you say you're "popping" relays, do you mean you're burning out the coil, or the contacts?

[pbs911]

Leland,
Can't help with the wiring, but an alternative is to take the heat blower and all releated hoses and throw them in the trash where they belong! Then go get some pre-74 heater pieces that move the air via the fan. The cost is about equal to what you have already paid in relays. Plenty of hot air, above idle, and you will lose about 12 lbs of stuff. Really cleans up the engine compartment too.

[marcesq]

Lee:

Jump the relay sockets that hold pins 30 & 87 of the relay with a piece of wire and see if the blower motor works, and whether it runs smoothly or after running a short while the speed varies.

At that point you will know if the motor is ok and the wiring is not a problem from fuse 23 to the motor.

As to 85, turn on the key and pull the heater levers. Put the + lead in the 85 hole of the relay socket, and - lead to ground (body metal unpainted)see if you get a reading.

Next turn everything off & push heat levers down. Set meter to ohms and put the + lead in the 85 hole of the relay socket, and - lead to ground this sould give you an infinity reading. Now pull the heat levers and the ohm meter should go to zero if it dosen't the switch is bad or the wiring between the relay socket and the switch may be bad.





I might be wrong, but the blowing of the relay is probably because 85/86 circuit is being exposed to more amps than it has capacity. If it is the 30/87 circuit that is blowing then the motor may be bad.

But with any electrical gremlin it may be non of the above.

Sorry that I couldn't be more definitive.

[Leland Pate]

*Gremlin found*

All it took was for me to put my hand in there and try to move the blower fan by hand.

"Yup... it won't turn."

So, I took it out and disassembled the thing, I found that one of the two screws that hold the motor plate onto the case had come undone and jammed itself between the motor case and the blower dealie.

So, I loctited everything and put it all back together.

Too late tonight to see if it works...
Will try tomorrow.


Whew!

[marcesq]

Lee:

Let me know how it turns out.

Marc