Early 944 heater blower help

Santos · 12-12-2010, 04:37 PM

Hello all,

I have an '83 944 non-turbo Porsche. The early 944 has seperate controls for the AC air fan and Heater air fan. My AC works fine.

My heater blower motor does not turn ON at any speed setting. I applied 12Volts to the heater blower motor directly and grounded to battery and the blower turned on at full speed. So, I know my heater blower motor is good.

With ignition set to ON, I connected a test light across the power connector to the heater blower. The bulb barely lights up no matter what heater speed I select. My VOLT meter indicates that the heater blower power connector has 12.5Volts at all speed selections. So, the dim light is due to insufficient current flow.

Could the issue be that the heater resistor is shorted?
This would cause most or all current to flow through the heater resistor and prevent most current from flowing through the blower motor.

My biggest issue right now is removing the heater resistor. What is the proper way to remove the heater resistor? The resistor connections look permanent and fused. I tried using my soldering iron but was not able to disconnect the wires going to the resistor. Am I suppose to CUT the wires off the resistor?

I plan to completely remove the heater resistor to allow all current to flow to the heater blower motor. I will not be able to vary the speed but I think I should see the blower motor kick ON at full speed.

Any tips appreciated...
thanks,
Santos

Santos · 12-12-2010, 07:06 PM

I found a crappy but better than nothing electric diagram for the fresh air heater system in a Haynes manual. I was under the impression that the heater speed resistor was in parallel to the heater blower motor. But, based on the electric diagram the heater speed resistor is in series with the heater blower motor.

So, now the 12.5Volt measurements are NOT making sense. I would expect voltage division for a resistor in series. The blower switch has 4 settings (OFF, 1, 2, 3). With the ignition ON, the blower motor connector had 12.5Volts in all switch settings including OFF. Maybe I have a bad console heater switch with a weak ground???

Slam · 12-13-2010, 08:11 AM

Looks as if you're on the right track. I just cut the resistor out and soldered in a better one on mine. You could also make sure the whole system is getting a good ground, too. You may not want your heater blower blowing at full speed. You'll end up getting slightly cooler air from it due to the heat exchange with the higher volume of air. If you want to hard-wire a speed, choose setting 2. The air moves slower but blows warmer. Take it from a Canuck!

HondaDustR · 12-13-2010, 08:35 AM

Maybe this would help.

The blower runs through a relay that locks it out when the AC blower is running. Could be the relay.

Santos · 12-13-2010, 10:40 AM

Thanks a ton to both of you. I'll reply with a fix soon, I hope.

btw, where is the Fresh Air Blower Relay located?

I only see FUSES for "fresh air fan". Upper fuse bank fuse #6 is for fresh air fan. Lower fuse bank fuse #10 is for fresh air fan. I do NOT see any fresh air blower relay in the relay panel layout. I only see a Cooling Fan Relay (#1) and an Air Conditioning Relay (#3).
Maybe the fresh air blower relay is part of the AC relay???

The heater fresh air blower motor has connections T2(1)(a) and T2(2)(a).
T2(1)(a) is GROUND.
T2(2)(a) is ~12V POWER coming from Fresh Air Blower Relay

If I connect T2(1)(a) directly to battery ground I will completely bypass the speed resistor and the heater fresh air blower switch. The T2(2)(a) connection is not modified and continues to draw power from the Fresh Air Blower Relay. If the blower motor turns on at full speed, I think I am safe to assume that the power coming from the "Fresh Air Blower Relay" to the blower motor is GOOD and I need to work on GROUND side of circuit.

Thanks,
Santos

Santos · 12-13-2010, 12:41 PM

Reporting progress. A light bulb is an electrician's best friend.

I connected my test light directly to battery ground and then I probed the air blower motor connector at the 12+ volts connection also known as T2(2)(a). The light was barely lighting up. This testing procedure bypassed the heater console switch and the speed resistor. The ground can't be any better and therefore the current coming from the fresh air blower relay is weak.

I also tried connecting my test light directly to the positive terminal of the battery. I then probed the ground side of the air blower motor connector. The test light lit up nice and bright. So, the ground through the switch and speed resistor is good.

Now, I just need to figure out where the Fresh Air Blower Relay is located. I wish I was as flexible as a contortionist. I'll try to figure out where the relay is by following wire colors.

~Santos

Santos · 12-13-2010, 09:04 PM

Here is an electric diagram for fresh air blower with AC.

I have a "fresh air blower relay" and a "fresh air blower interlock relay" to work with. I tried my best to trace the red power wire that connects to the heater blower motor. I went under the dash on driver's side and traced all wires to the heater console switch. I was tracing the red power wire but I loose it above the DME unit. So, I failed to find the "fresh air blower relay".

Where is the "fresh air blower interlock relay"? From searching the website, I read someone say the relay is in the passenger side under the dash next to glove box.

Santos · 12-14-2010, 02:40 PM

Finally traced the red power wire from the heater blower motor to the Air Conditioning System relay. So, the same AC relay is used to power the AC blower motor and the Heater blower motor.

I did a continuity check on the red power wire from the relay connection to the blower motor connector. The power coming out of the relay into the heater blower motor is weak. All other connections to relay have good power and ground.

Autozone does not carry AC relays for the 944. Pelican parts is out of Air Conditioning System Relay which by the way are $60 !!! What an expensive relay...

Has anyone used the "Multi-Purpose Relay" that Pelican sells as an A.C. System relay?
Relay Part #: 141-951-253-B-M5206

Pelican Parts - Product Information: 141-951-253-B-M5206

Jrboulder · 12-14-2010, 02:55 PM

I am going to carquip tomarow, I could pick one up for you if you wanted me to...

Santos · 12-14-2010, 04:57 PM

Thanks Jrboulder but I managed to fix the issue without spending $$ on a new relay.

I used the Rear Window Defroster relay #6 to replace my Air Conditioning System relay #3.
I have the early '83 944 Porsche and the relays turned out to be exactly the same.

My heater blower is working great now. AC blower continues to work as always.

Thanks to all for the help and sharing of electric diagram.

HondaDustR · 12-14-2010, 09:07 PM

Relays are usually pretty simple and can often be fixed. Just work the cover off with a small flat head screwdriver or 2, clean the contacts with some emery cloth or very fine sandpaper, re-melt the solder joints if any, and pop it back together. Certain relays have a diode or some other simple component that can usually be found at radio shack if needed.