rastapapa

Hello,
The other day in my 1982 928, I turned the defrost on and after a second of it working the entire blower stopped working. By stopped working I mean that the blower motor does not come on no matter the setting of the climate control.

I tested ths fuses and pulled the hvac blower relay and jumped the terminals and the blower went on, and with the jumper in the blower works correctly changing speeds when you turn the dial from 0-3.
So I pulled the jumper and put in a new relay. No luck. It seems that power is not getting to the relay coils.
I then tore out my climate control unit and opened it up and didn't see anything wrong. I cleaned up the terminals since I was in there, but no luck.
Ive been looking at the current flow diagrams, but I cant figure out what would be preventing power from getting to that relay.

Any ideas?

Thanks
Oliver

Mrmerlin

you have 2 relays for the blower system XXI and XXII, try swapping out the other relay with the horn relay they are all 53 relays, replace the blower fuse

rastapapa

Thanks Mrmerlin. I did swap out both the XXI (hvac blower) and XXII (defroster) relays with new ones from 928intl with no luck. I might try replacing the fuses just to be safe, but the electrical diagrams seem to show that it the fuses are to protect the current through the switching contacts, not the coils of the relays. Am I wrong?

where can I test to see if the power is being switched to the relays?

Ive searched the forums and found two other things to try, but Im skeptical of both.
Number One is the resistor pack that claims responsibility for mystery blower syndrome from this thread:
https://rennlist.com/forums/928-foru...quick-fix.html
but I think that this controls the speed of the blower, which is not my problem - the speeds work fine when I jumper the relay terminals.

And Number Two is other this weird link:
http://www.nichols.nu/Tempctrl.pdf
but I dont really know what it does.

Thanks for the help

Mrmerlin

swap out the fuse first

WallyP

Check Fuse #9, and carefully check the fuse connecting clips for corrosion and tightness.

rastapapa

You nailed it Wally! Fuse #9 was busted! Thanks so much! The blower is now working!!

Howd you know? And can you tell me why fuse #9 (Backup Light, Mirror Motors) knocks out the power to the blower relays?

Also just before this blower went out, my window winder relay went bad. Any ideas of why this might be happening now and what I can do to try eliminate it from happening again?

Thanks again.
Oliver

rastapapa

I took a look at the flow diagrams again and tracing fuse 9 you can go through several pages and low and behold you do find a wire that goes into the climate control unit. I am new to these drawings, and porbably wouldnt have guessed that that fuse was responsible for the climate control power. Is it because it is a black and white striped wire going in to the unit?

WallyP

The power for both relay coils comes from the Heater Control Assembly. If you look at Zone 14 on Page 97-135, you will see the power supply for the Heater Control Assembly coming in on the black/white wire from L6. If you follow the internal line from L6, it leads you (over several pages) to Fuse #9.

Glad that it was so easy to fix!

rastapapa

not as easy as I had hoped. Fuse 9 keeps blowing. It seems the most it lasts is a week of normal driving and using the heat. Any ideas on how to troubleshoot this one?

WallyP

Could be tough. It is much easier to find the problem if the fuse blows instantly...

One possibility is to try cutting off circuits powered by Fuse #9 and see if that stops the fuse from blowing.

As an example, #9 feeds the backup lamps and the rear window wiper. If you disconnect the black/blue wire from S7, it will disconnect that circuit. Run for a week or two - if the fuse blows, reconnect the circuit and start checking these two items.

If it doesn't blow, reconnect the circuit and disconnect the red/white wire at F1 that feeds the outside mirrors.

If the fuse still blows, reconnect the wire at F1 and start checking the HVAC system...