backitoff

I have an intermittent blower problem when driving along. I thought it was the air sampler or a bad connection but can find nothing.
I have a spare CCU which I have swapped over to try and still have the fault.

Interestingly if I turn the heat control to coldest the blower comes back on.
Here is a list of what I have checked so far;
All flap / solenoid motors are working
Both blower motors in good condition
Rear flapper boxes now working freely
New blower relay
Replaced 1x mixing chamber temp sensor, both now reading the same ohms.
A while back I did the rear blower delete and ran a permanent live from the coil to the relay socket so thats ok too.

I'm at a loss now what to do next. Is this likely to be something related to the mixing chamber temp sensors? or the blower rheostat on the front firewall?

Any other suggestions / help would be appreciated.
Thanks

BGLeduc

I will be watching this thread closely because I just now encountered avery similar problem.

I do note that I get little air movement (and thus heat), but I can not increase the airflow.

I am also just now starting a search, which is how I found your thread.

BGLeduc

Found this in another thread.

It appears I have a rear blower issue.

http://www.bergvillfx.com/porschehvac1.html

Outstanding website BTW.

David A

Time for a Heater bypass?

http://www.patrickmotorsports.com/pa...ht-heat-elbow/

JJ964

I had a similar problem. I noticed that the CCU appeared electrically dead when it happened so I pulled the fuses associated with the CCU (3 I think) sprayed contact cleaner in the sockets and "exercised" the fuses. I had a 99.9% improvement.

Kuchar

I had similar problem too. Probably, the cause of the fault is a dirty temp sensor in CCU. In my car it happend twice. Somwhere on RL is a thread about it.

Kuchar

https://rennlist.com/forums/964-foru...em-solved.html

WA3FRP

I had the problem of no blower except when the temp was set to cold (counterclockwise) and thought that the CCU was defective. After I swapped it with no improvement, I discovered that there was a blown fuse on the engine compartment. If you haven't done so, check to see the condition of fuse 1. This is a 30A fuse. If you have a lower value fuse and a 1989 C4 and maybe a 1990 C2, please note the technical bulletin from 15 December 1989 (8904) that reports 25A is too low a value for this circuit.

ToreB

Kuchar, I would like to point out that intermittent front blower behaviour will not be caused by a dirty cabin temperature sensor in the Climate Control Module. In your case you probably had a slightly corroded or dirty fan speed potentiometer.

A dirty interior/cabin temp sensor will make the cabin temperature to decrease during driving.

The most common cause that makes the front blower fans to shut down is a failing rear fan circuit. (motor/fuse/low speed resistor)
See my HVAC pages for details: www.porschehvac.bergvill.com

Cheers,
Tore

BGLeduc

I can report that my heater fan issue was due to a blown 30a fuse.

Interestingly enough, the inside cover of the rear control box still had the fuse removal tool and the spares for the 7.5 and the 25, but the 30a was missing. I can only assume that at some point prior to my purchase in 2001, someone must had had to use it. Luckily I had one.

Massive thanks to Tore for his fantastic web site. I had no idea that there was a separate control box in the engine bay. I would have struggled to troubleshoot the problem without the great instruction and photos from your site.

Brian