dead heater fan and window?

[Bob Turner]

Hi all

I am normally over on the 993 forum, so be gentle.

Just commissioning my 1990 964 C2 after a longish cosmetic rebuild/chassis rebuild. The cabin blower doesnt work. Checked fuse 1 which was blown it a d replaced with 25A fuse. No change. Swapped the relay with relay 04 (oil coller blower) no change. Have tried it with the demist button and the multispeed button.

I hate bloody electrical problems. :frustrated:

Without the engine running, I can just hear a fan turn slowly for a few secs and then stop. The engine is cold, so the rear blower should not make any difference ? :dont know:

Am i looking at pulling out the dash to replace fans/lubricate them? :nooo:

Are there any relays or other parts that I can borrow from my '94 993 C2 and try out?

Also one dead window. The other works so the fuse and realy are OK I think? Any ideas on this ? :question:

many thanks

 

[TommyC]

there is another fuse. perhaps that one has also blown. number 17 i think - have a look on the fuse list.

good luck.

 

[Bob Turner]

fuse 17 is good too. Anyone else got some ideas pls.

 

[Computamedic]

As you probably already know, the 964 (and 993) HVAC system is quite complicated and the operation of many things often depend on the correct operation of other things. Trying to diagnose problems often entails quite detailed sequences in order to isolate which bit isn't working.

If the cabin fans don't operate at all, regardless of what temperature is selected, it would suggest either a fuse blown or the main driver amplifier gone U/S. Don't attempt to pull out the dash to get to the fans because they are on the other side!! It's a fuel tank and firewall removal job I'm afraid.

It's worth checking if the rear blower operates - it should switch on when you select a temperature a little beyond the blue dot on the rotary control. If the rear blower doesn't start up with the temp selector towards the red dot the cabin fans won't start anyway. You need the temp selector on the blue dot to be sure you are testing the cabin fans.

If the cabin fans start up on blue dot temp and stop when moved towards red dot the problem is the rear blower. If they don't work at all on any temp setting and the fuse are OK it's almost certainly the driver amp (behind the fuse box) or the main CCU at fault. The CCU also controls the oil cooler and condenser fans so worth checking if they work.

Hope that helps.

Regards

Dave

 

[Bob Turner]

Thanks for that dave. I think it is more than the rear blower not working as the I get zero when the temp dial is not the blue dot. Any diea what I should be seeing from the driver amp? I have an old AvoMeter somewhere, and a 'scope. Is just a voltage/current I should be looking for are some nasty signal with a carrier wave?

 

[Computamedic]

Bob,

There's a lot that you DIDN'T say in your reply that might be more of a clue. What DOES happen with the temp selector on the blue dot?? Do the cabin fans operate at all??

The usual scenario is that the cabin fans operate over the full speed spectrum with the temp selector on the blue dot. Move the temp selector towards red and the cabin fans stop. If the cabin fans are OK on the blue dot it eliminates the final stage driver as a problem.

Can you confirm if the rear blower runs?? If not, further diagnosis is difficult since so much depends upon it.

Regards

Dave

 

[Bob Turner]

Thanks for the reply again. The cabin fans do not run when the temp is on the blue dot. I haven't looked at the rear blower. I will do on Saturday when I am home again.

I have similar issue with my 993, which almost certainly is the rear blower fuse, as the fans run on the blue dot, but not when the temp control is off the blue dot.

Any idea on the window. Seems there is only one fuse for both windows, and one of them works fine.

 

[Computamedic]

Bob,

A common problem with the windows is the switches. Bear in mind that the passenger window needs BOTH switches to be operational since they are wired in series. Swapping switches from side to side won't help unless you substitute a known good switch (from the driver's windows).

The cabin fans not operating on the blue dot suggests the final driver amp is toast.

Regards

Dave

 

[Bob Turner]

Thanks again. Switches should not be too hard to check out.

I believe the driver amp sit under the fuse box. Is that right? What should I be seeing as the amp input and output. Is fan speed just dependant on voltage like the oil cooler fan 8v/12v. Is t here a simple/lw cost replacement for the amp?

 

[Computamedic]

Bob,

Correct - the driver amp is just behind the fuse box. The fan speed is continually variable (unlike the blower and oil cooler fans) - hence the driver amp.

They come up on eBay all the time although I can't find any at the moment. New ones are around £400+ from memory.

Regards

Dave

 

[Bob Turner]

Hi again Dave.

Still not getting anywhere, but I have a bit more info.

Have changed both relays 04 and 14 for known good ones from the 993. Changed fuse 01 as whilst it looked OK it might not have been. Turns out is wasn't as a new fuse blew immediately I turned on the fan.

I took the light plastic trim off that covers the fans and air circulation valves etc.. but I am having trouble identifying the driver amp.

I was thinking I would try 12volts directly to each fan to see if thay run or are siezed. i.e try and eliminate the fans before the amp. Is this good thinking or not?

await your knowledge.

many thanks

Bob

 

[Bob Turner]

Hi Dave

Another hour of getting no where. I can't even find the wires that connect to each blower. Maybe they go in underneath. I did discover that the black and brown wire in the loose fitting black sheath on the driver side blower (LHD car) are not connected to anything. They may even have been shorting out as there is just longish (2cm) pin on the end of each wire. I also found tha that the grey sheathed wire go to some kind of temp or flow sensor, as I removed one of those and refitted it thinking it might have been the blower fan connection.

Which blower is the normal heater, and which one is the windscreen demist?

 

[Computamedic]

Bob,

It sounds like it's getting complicated!! The final stage amp is fitted vertically behind the fuse box (between it and the firewall) with the connector at the top. It consists of a small electronics box attached to a BIG aluminium heat sink that's roughly triangular in shape.

The two blower fans are used in parallel, i.e. they are both used for heater, a/c, demist et al. The final stage amp varies the voltage to the blowers in order to control the (continuously variable) speed.

I'm struggling to give you much more information as I've not taken mine apart

Regards

Dave

 

[Bob Turner]

thanks Dave. All fixed. See other thread.