1990 911-964 3.6l a/c

fleetline51 · 07-08-2009, 01:36 PM

just got this car on the road and havin' fun!

A/c won't work...seems that the fan is not running...any ideas?

Thanks much in advance!

Tony

dmwallace · dmwallace's Garage

Maybe check fuses and relays?

Oracle · 07-08-2009, 07:10 PM

maybe a bad climate control unit? Hook the car to the diagnostic tool and take it from there.

computamedic · 07-09-2009, 04:58 AM

When you say "the" fan it would be helpful if you could clarify. There are no less than 4 fans involved with the a/c - 5 if you include the sampler fan on the CCU itself.

The common problem area is the rear blower. If that doesn't run very little else will work. Problems can be blown fuse (MUST fit 30 amp fuse despite label maybe indicating 25 amp), failed relays (swap with oil cooler relay up front to check), problems with the ballast resistor (in the blower trunking) and potential problems with the CCU itself. The cabin blowers are controlled by a solid state amplifier attached to the firewall driven by the CCU and the condenser blower also driven by the CCU via it's own relay (same as rear blower relay) in the main fuse box. Where do you want to start???

Regards

Dave

fleetline51 · 07-09-2009, 05:28 PM

OMIGOD!

You Guys are Scarin' Me! LOL

I will search out - one by one- the advice given me ...Thanks SO MUCH for Your insight!

HOW MANY FANS?

computamedic:

Thanks especially for the "in depth" directions...

" I'll Be Back."

Thanks Again,Folks!

Tony

fleetline51 · 07-10-2009, 04:00 AM

Quote:

Originally Posted by computamedic

When you say "the" fan it would be helpful if you could clarify. There are no less than 4 fans involved with the a/c - 5 if you include the sampler fan on the CCU itself.

The common problem area is the rear blower. If that doesn't run very little else will work. Problems can be blown fuse (MUST fit 30 amp fuse despite label maybe indicating 25 amp), failed relays (swap with oil cooler relay up front to check), problems with the ballast resistor (in the blower trunking) and potential problems with the CCU itself. The cabin blowers are controlled by a solid state amplifier attached to the firewall driven by the CCU and the condenser blower also driven by the CCU via it's own relay (same as rear blower relay) in the main fuse box. Where do you want to start???

Regards

Dave

Does anyone here have schematics or wiring diagrams so I can check some of this stuff?

Any help would be greatly appreciated!

Thanks Again! Tony

cjoenck · 07-13-2009, 04:05 PM

Send me a pm with an e-mail. I might be able to help with a wiring diagram

fleetline51 · 07-14-2009, 05:09 PM

Quote:

Originally Posted by computamedic

When you say "the" fan it would be helpful if you could clarify. There are no less than 4 fans involved with the a/c - 5 if you include the sampler fan on the CCU itself.

The common problem area is the rear blower. If that doesn't run very little else will work. Problems can be blown fuse (MUST fit 30 amp fuse despite label maybe indicating 25 amp), failed relays (swap with oil cooler relay up front to check), problems with the ballast resistor (in the blower trunking) and potential problems with the CCU itself. The cabin blowers are controlled by a solid state amplifier attached to the firewall driven by the CCU and the condenser blower also driven by the CCU via it's own relay (same as rear blower relay) in the main fuse box. Where do you want to start???

Regards

Dave

Dave:

Went as far as checking fuses, (yes..ALL of them! lol) relays, wire connections and
male/female plugs that I could find. Everything checks okay so far.

Where-exactly- might I find the ballast resistor in what You call the "blower trunking"? Might that be what We here call the "front or forward trunk " compartment where the spare tire is kept?

Thanks Again!

Tony

computamedic · 07-15-2009, 12:57 AM

Tony,

The ballast resistor is clipped to the side of the plastic trunking that directs the rear blower airflow from the blower into the heat exchangers under the engine. You'll find the ballast resistor just opposite the cover for the rear electrical panel on the left side of the engine compartment. There are two wires attached to the resistor and it just clips into the plastic tube. It looks like a coil of wire once you have it out. The newest type has a bi-metal strip safety cut-out and it will prevent the blower running at slow sleed if the safety has tripped. You can press the safety to reset it.

Dave

fleetline51 · 07-15-2009, 02:20 PM

Quote:

Originally Posted by computamedic

Tony,

The ballast resistor is clipped to the side of the plastic trunking that directs the rear blower airflow from the blower into the heat exchangers under the engine. You'll find the ballast resistor just opposite the cover for the rear electrical panel on the left side of the engine compartment. There are two wires attached to the resistor and it just clips into the plastic tube. It looks like a coil of wire once you have it out. The newest type has a bi-metal strip safety cut-out and it will prevent the blower running at slow sleed if the safety has tripped. You can press the safety to reset it.

Dave

You Guys Rock...Except, now I'm REALLY confused!!!

When I mentioned that -"The blower wasn't working"- I really should have stated that "The cabin fans were not operating".

In other words,When I turn the (5) speed fan switch on the dash,nothing happens....no air is being delivered via the air delivery vents.

As I mentioned , all the fuses are good...Relays fire...(also bench tested relays with 12 volt power supply)... I turned the fan switch on and then went to the relay
section, pulled the blower relay and heard it "click" on and off as I unplugged and then plugged it back in.

Does the ballast resistor have anything to do with the cabin fans?

What else can I check?

As I operate the a/c switch to the "on" position,I can hear the compressor kick in
and the engine labor under the load...all the switch pilot lights operate...

But no fans!

Any help would be Greatly appreciated!

Thanks! Tony

computamedic · 07-16-2009, 12:05 AM

Tony,

The interaction between the rear blower and the cabin fans is not as tenuous as you might think. You need to do some controlled tests to establish what is happening.

With the ignition on and the engine off, turn the temp dial to the blue dot and the fan speed to 0. The rear blower should be off at this point. Then turn the temp dial half way towards the reed dot. You should hear the rear blower start up ar slow speed. If it doesn't start up you have a problem there first. Until you resolve that problem the rest of the testing is going nowhere.

If the rear blower DOES start, turn the fan speed to 2. You should then hear the cabin fans start up. If not it would suggest a problem with either the CCU itself or, more commonly, the final stage amplifier which drives the fans. The fan switch is not a 4 stage fixed speed selection - it's continuously variable and the drive to the fans is controlled by the final stage amp attached to the firewall behind the fuse/relay box. It's a common failure and they come up on eBay quite regularly.

The a/c is irrelevent in this testing - in only confuses the issue. Once everything else is working you should find that pressing the defrost button will get everything going at full speed - cabin fans, rear blower and a/c condenser fan.

Regards

Dave

fleetline51 · 07-16-2009, 03:03 AM

Dave,

I will pick up on Your recommendations first thing after work Today.

Your advice and the help You and the others have provided is invaluable!

Will get back soon with the results.

Best Regards,

Tony

fleetline51 · 07-16-2009, 05:49 AM

Quote:

Originally Posted by computamedic

Tony,

The interaction between the rear blower and the cabin fans is not as tenuous as you might think. You need to do some controlled tests to establish what is happening.

With the ignition on and the engine off, turn the temp dial to the blue dot and the fan speed to 0. The rear blower should be off at this point. Then turn the temp dial half way towards the reed dot. You should hear the rear blower start up ar slow speed. If it doesn't start up you have a problem there first. Until you resolve that problem the rest of the testing is going nowhere.

If the rear blower DOES start, turn the fan speed to 2. You should then hear the cabin fans start up. If not it would suggest a problem with either the CCU itself or, more commonly, the final stage amplifier which drives the fans. The fan switch is not a 4 stage fixed speed selection - it's continuously variable and the drive to the fans is controlled by the final stage amp attached to the firewall behind the fuse/relay box. It's a common failure and they come up on eBay quite regularly.

The a/c is irrelevent in this testing - in only confuses the issue. Once everything else is working you should find that pressing the defrost button will get everything going at full speed - cabin fans, rear blower and a/c condenser fan.

Regards

Dave

Hi Dave!

Did all the above...also pulled the ballast resistor...reads about (5) ohms from terminal to terminal...it looks okay.

No dice on the sequential testing, though...nothing happened when I
went through the procedure as You described...

When I put my stethoscope probe against the dash control panel, I can hear a
definite sound...almost like a small fan running.It continues for a while until it stops.I can hear it without the stethoscope...I just used the scope to try to pinpoint the location of the sound.

Where do You think I should go from here?

Thanks so much, Bud!

Best Regards, Tony

computamedic · 07-16-2009, 11:34 AM

Tony,

The reason you can hear a fan running on the CCU is because there is a fan running on the CCU!! There is a small sampler fan which draws air through the grille on the front of the CCU over the temperature sensor just behind the grille. The fan will usually run for around 10 minutes after ignition is switched off.

If the testing doesn't result in the rear blower running you'll need to do some checking with a voltmeter to see if the blower relay (in the rear electrical panel) is getting activated. If not, the chances are that it's the CCU at fault. If the rear blower doesn't start up there's not much chance of anything else running as it should. A/c on with temp on the blue dot doesn't require the rear blower but you should hear the condenser fan running.

Driver transistors and bad solder joints are common problems with the CCU - all mostly really cheap repairs if you have the time and inclination to chase them.

Regards

Dave

fleetline51 · 07-17-2009, 05:36 AM

Dave: ...

Once more, a large THANK YOU for getting back to Me so timely with Your knowledgeable information!

A few more for 'Ya:

Is the Cabin Control Unit the dash mounted panel with the a/c-fan switch-temp control-etc. mounted to it?

How is it removed? Do I need special tools?

are there any other components in the luggage compartment(besides the fans)
that need to be addressed?

Thanks again Dave!

Best Regards, Tony

computamedic · 07-17-2009, 07:37 AM

Tony,

The Climate Control Unit uses the same fittings as a radio of the period - you need two forked prongs to fit into the holes each side which release the retaining clips. It then just pulls out of the slot. The large connector on the back needs to be released before you can pull the whole thing out.

The cabin fans are an integral part of the HVAC unit which is installed in the luggage compartment behind the firewall. There is some limited access having removed the top plastic cover than runs across immediately in front of the windscreen but any major work involves removing the fuel tank and firewall. Not for the feint-hearted I'm afraid.

Regards

Dave

fleetline51 · 07-20-2009, 01:21 PM

Okay...
Pulled the CCU out of the dash-seems that someone was there before Me-

some hand written markings on the outside case-a circled "X" was clearly readable.

At any rate,I pulled ALL the internal components apart.

Note: I spent 45 years in electronic manufacturing-specifically printed circuit board
manufacturing- so I am certainly no slouch when it comes to pc's and pcb assemblies.

No apparent bad news...could not identify any anomalies even with an inspectors eye loupe.

I DID notice one thing: The air sampler sensor probe apparently had a failed connection due to a cold solder joint...I cleaned the fine wires of the probe and carefully soldered them back together.

Re-assembled everything and re-installed the unit back into the dash.

Went through the start-up procedure...no dice.

No cabin fans-no rear blower-no nuthin'!

Am looking for someone around My parts with a Bosch "Hammer" so I might be able to run some error codes.

Has anyone here ever attempted to by-pass the CCU in such a manner to get things "working" temporarily?...until I perhaps get a handle on what REALLY is causing this problem.

Thanks Folks!

Best Regards, Tony

wrx paul · 07-22-2009, 08:48 AM

Pardon my highjacking this thread but I'm hoping one of you experts can help me also.

On hot as hell days my drives side heat is on, even after I have removed the cable pull for the flapper box on the servo under the hood.

However on cooler days it doesn't seem to be on, so I'm hoping maybe you guys know of a part that is causing the rear fan to blow the hot air through when it's not suppost to??
My AC is working fine and it can just about balance out the heat on those hot days and luckily enough it come out cold on the passenger side so the car is drivable in 80+ heat.

fleetline51 · 07-23-2009, 04:44 AM

Can't remember where I saw a repair service for Porsche Climate Control Units.

I think it's that time....Any Help?

Thanks! Tony

CliffBrown · 07-23-2009, 09:00 AM

Quote:

Originally Posted by Fleetline51

Can't remember where I saw a repair service for Porsche Climate Control Units.

I think it's that time....Any Help?

Thanks! Tony

Tony

I recently saw an ebay listing for fixing the CCU.