Dan87951

Hello! My dad's HVAC system in his 85S is completely dead. He said over summer he was driving with the AC on and everything was working fine until it just died and a puff of smoke came out the temp sensor hole on the front of the dash. Every since than none of the blower motor settings work. Actually, nothing works AC, DEF, or heat as I cannot get the motor to spin. I did some checking and the AC fuse was blown as well as fuse 17 (blower motor). It's almost like everything just died! Below is what I have checked so far:


1. Replaced Fuse 17 (blower motor fuse) and no change, still dead.
2. Swapped HVAC control unit from another car and still no function on any settings. Almost like its dead.
3. I checked power at the blower motor and I'm get .220-.228 volts so pretty much dead.
4. Swapped the blower motor relay and still no change.

Could this be a resistor pack I keep hearing about? I heard if the pack fails that you still have some function with the blower motor but I have nothing, so I'm thinking it could be more serious? Let me know what you guys think as I'm lost now.

Thanks

AirtekHVAC

I was thinking resistor pack meself....or motor...my motor went bad

Dan87951

So the resistor pack can cause the motor not to work on all settings? thanks!

Just an update: I hooked up a 12v battery directly to the blower motor and its working fine. I think my problem lies in not getting 12v to the blower motor. What supplies the power feed to the motor?

SeanR

If you got a puff of smoke out the inside temp sensor, you have other issues. The fan inside that sucks air in and takes a reading. I think you are going to need to pull your center console and find out where that puff of smoke came from, to me it sounds like something shorted out and needs to be replaced.

AirtekHVAC

Oh....there is also a relay....when mine died, it was actually locked up, and the relay smoked...

Mrmerlin

I would pull the resistor pack out of the duct and test it,
since the sensor in console sucks air in,
this can be tested with simply putting a cigarette near the opening and see if the smoke is sucked into the hole NOTE this with the HVAC system on,

BUT check the resistor pack and the blower motor relay first

WallyP

1) Pull Relay X, the Blower Relay. Look at the diagram on the side, and locate Terminal 30 in the relay socket. Use a test light to check for power on Terminal 30 - there must be full battery voltage. If so, go to 2). If not, the fuse contacts on Fuse 17 are probably faulty.
2) If you have power on Terminal 30 of Relay X, install a temporary jumper between Terminals 30 and 87 in the socket for Relay X. Try the blower switch. If the blower works normally, the Resistor Pack is OK. If the blower works only on the highest speed setting, there is a broken resistor wire in the Resistor Pack. If the blower doesn't work at all, there is a faulty connection somewhere between Terminal 87 and the blower motor.
3) If the blower works at all, remove the relay jumper and install Relay X in the socket and repeat the test. If the blower works exactly the same with the relay as it did with the jumper, you should now know what the problem is. If the blower does not work at all with the relay installed, swap Relay X and Relay VIII (the Defrost Relay). If the system still does not work, you probably have a failure in the HVAC Control Unit or elsewhere. The most common failure is the small relay inside the unit. This can be replaced.

It is possible that you have a problem with the cabin air temp sensor - perhaps the fan motor - but do the suggested tests first.

Alan

No the resistor pack has nothing to do with the max setting or the DEF setting - either will work with the resistor pack unplugged - so it isn't that.

What stops the fan on full speed is the motor itself (you say it tested OK), the fan switch (could be unplugged), the blower/HVAC fuse, The blower relay (or the DEF relay) and the presence of a ~working head unit required to turn the blower relay on.

What caused the fuses to blow is probably the thing you need to know...?

Are the replaced fuses still good - replacing them isn't whats important - its if they continue to blow and what exactly causes that...?

Alan

Dan87951

Wally, thanks for the detailed info it really helped!

I do have 12volts at terminal 30. I installed a temporary jumper between terminal 30 and 87 as outlined in your instructions and the blower motor is working good on all settings so my resistor pack is ok! If I reinstall the relay nothing works again. I tried a few of them and no luck on any of the relay's I have. Since my blower motor is not working when reinstalling the relay and I'm positive its not my HVAC controller (pulled from my working car for testing), what else could it be since the motor and HVAC are ok??

Thanks

Edit: Would the in car temp sensor to the right of the blower vents cause the blower motor not to work? Under closer inspection I believe this is what got real hot and gave out the puff of smoke. By looking at the temp sensor it looks burnt and also has a white ashy substance on the end.

Mrmerlin

..

Alan

See my previous list - check the blower switch connector 1st.

Not directly - but it could have taken out the HVAC head unit...? The head unit has to operate to turn on the Blower Relay (and the DEF relay). For the temp sensor to give up any smoke - I think you had to have a short on the sensor loop (any work in the console/drivers front fender recently?) - its not normally under any stress.

It is most likely the sensor went puff in max heating mode (temp slider all the way to the right...? ring any bells ?). Check (test?/replace/test? again) Fuse #8

Alan

dzaprev

Check the relay jsut had same thing happen. $5.50 at Pelican

Dan87951

Hi Alan,

What do you mean by the "blower switch connector"? Are you talking about the connectors on the side of the HVAC unit? If so those are fresh and cleaned and have good contact.

Yes we did replace the dash board with a recovered unit from 928 Leather shop about a year ago. Just to recap we have three 928's in our family and I'm able to swap parts for testing. So far the HVAC controller and relay's are all from a known working car. The blower motor has already been tested as working as well.

I wasn't in the car when the puff a smoke came out. My dad said the AC was on when it failed though. He did mention after just talking with him that the air temp sensor was glowing red and a puff a smoke came out and everything died.

Alan

The HVAC blower speed switch has a separate connector, also on the HVAC module.

Check fuse #8 - if you haven't checked it yet that's what I'd suspect.

You can't see the sensor down the sensor hole - so not sure what was glowing red...?

Alan

Dan87951

Fuse #8 is fine. However my relay VIII (defrost relay) has a test port on the top of it. What is this used for? Can I test it with out pulling the relay out and swapping it. At the moment I'm having issues pulling VIII relay out.