8 cylinder front engine iconic vehicle
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By chalkboss
Really frustrated over this, and I'm guilty of throwing parts at a problem I don't fully understand. A few years ago I replaced my resistor pack with a newer style GTS part. I re pinned it as instructed and it worked fine, all speeds worked. Recently only high speed works, any position of slider. So I replace the blower motor and clean the resistor pack. Works fine the first time I start it, at all speeds. A few hours later I start it again and only have high speed. So I order and installed a rebuilt head unit today. Zero change, still high speed only.

I have a volt meter but I'm not very good with it. I don't understand what the problem is. Seems like a resistor pack but I don't know how that works or what to look for. Thanks for any help.
By SeanR
This '82 I'm working on did this to me yesterday. Put a new blower relay in and it started working. What's odd is I had already replaced that relay with a new Bosch, and that one works in other positions, but it didn't like being in there for the fan.

Remember, the high speed portion of the fan is controlled by the defrost relay.
By chalkboss
Makes sense now, of course. I'll check it tomorrow. How many times have I heard the mantra relay relay relay :cussing:

In my defense the blower motor was nasty looking and worn and the head unit had a wonky microswitch so I'm convincing myself it wasn't throwing money away.

By chalkboss
Couldn't help it so went out and swapped relays. No change. I did notice the relay was getting warm. I tried the back up light relay too which is the same and no change.
By Crumpler
As a shameless parts replacer myself I advocate these decisions!
It’s also important to support our 928 vendors;)
By chalkboss
I put new blower and defrost relays in, pulled relatively new resistor pack and cleaned it again, no broken wires. Still only works at high speed. Like I said before the head unit has been rebuilt, which also did not solve problem.
By Mrmerlin
I would pull the HVAC head unit and verify the connector is properly installed
By chalkboss
Figured this out finally. Swapped in another resistor (same part no) and it works! After some gentle poking around this small metal tab fell out of the thermal switch (I think that's what it is, a blue block). It's not broken, just fell out. I've ordered another part. God it was driving me insane and lightened my wallet.
By chalkboss
And before anyone tells me how to put the tab back in NO! I'm done messing around with this :cussing:
By Mrmerlin
FWIW on the restoration of the 82 I am working on,
the blower motor lower bearing seized and tore the bearing out of the motor casing.

Once that happened the fan was rattling around in the blower case.
This damaged the resistor pack and caused it to overheat.
A good used resistor pack from 928 INTL , and a new fan motor from Roger at 928sRus solved the issues
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