Engine Compartment Blower Motor, no power

[cmcfaul]

I ordered a replacement engine Blower motor as mine is clearly shot. I also so ordered a replacement Temperature Switch on Crankcase Breather Cover as I broke mine a while ago when replacing fuel lines.

I tested the connector to the motor (with defrost on) and there is no power at the terminal. I checked all the fuses in the front and all is good . I dont think the Temp switch would cause the motor to not have power, or am I mistaken.

Thanks,

Chris
89 Carrera

[redridge]

read through this https://forums.pelicanparts.com/porsche-911-technical-forum/1096426-heater-blower-motors-suddenly-inoperative.html

[aj88cab]

When you say "defrost on" are you referring to the dash fan switch? The dash panel switch does not operate the engine blower. The lever between the seats does, pulling up on the lever, with ignition ON. If the lever is what you mean, there are also fuses at the rear fuse panel for the engine blower to check. Also the controller on the engine relay panel may be bad.

Do you have Auto-Heat or a Manual system?

The temp switch would probably not cause the issues you are describing.

The link above, and the links in the link, have enough info to keep you reading for the weekend

[cmcfaul]

I have automatic heat control. Activated by pulling the two heat levers between the seats.

Will check the fuse in engine compartment. New parts dont come until Fridsy

[proporsche]

i wonder if your relay is not good ? Check the power to it this one

[cmcfaul]

Fuse was blown in the rear. I now have power to engine compartment blower terminals. The two fans inside the car have not come on. I forget if they are supposed to.

Will put it back together next weekend when parts arrive. Not sure how to reach the temp switch on the breather cover without taking off the throttle body.

Chris
89 Carrera

[wazzz]

The two fans inside will only come on once you put the engine compartment blower back in and plug its connector. This is because this blower needs to draw current thru the coil around the reed switch. Only then can the reed switch close contacts and let the inside fans be supplied with power. All this happens inside the heater control module pictured above by Ivan.

[cmcfaul]

Thanks Wazzz. that makes sense

[proporsche]

also..your 911 have ,on each of the interior blower, separate inline fuse..the fans will only come on the 6th and up postition
check that too

Ivan

[mysocal911]

Originally Posted by wazzz

The two fans inside will only come on once you put the engine compartment blower back in and plug its connector. This is because this blower needs to draw current thru the coil around the reed switch. Only then can the reed switch close contacts and let the inside fans be supplied with power. All this happens inside the heater control module pictured above by Ivan.

Correct! Typically this blower relay is damaged the result of an over-voltaging alternator or battery charger, i.e. the blower relay's internal relays' windings become open.

[wazzz]

Originally Posted by mysocal911

Correct! Typically this blower relay is damaged the result of an over-voltaging alternator or battery charger, i.e. the blower relay's internal relays' windings become open.

Both my internal relay's windings are shot open. I am currently trying to find replacement relays for both. Winter is here too in France. The bigger relay is more or less standard and can be found, but I cannot find anything close to the smaller one in terms of size and pin layout. This is the one that drives footwell blowers. If by any chance you or someone else has a source for a replacement, that would be great.

[proporsche]

vazzz....did you ask at type 911 French forum? Also what exactly is the small relay you are looking for?Any part number?Or is it the interior part? i have one used-which was open already- also if that is what you are seeking?
Ivan

[mysocal911]

Originally Posted by wazzz

Both my internal relay's windings are shot open. I am currently trying to find replacement relays for both. Winter is here too in France. The bigger relay is more or less standard and can be found, but I cannot find anything close to the smaller one in terms of size and pin layout. This is the one that drives footwell blowers. If by any chance you or someone else has a source for a replacement, that would be great.

I forgot to mention that the reed relay also fails. The reed relay controls the small relay's coil.

[wazzz]

@ Ivan, yes of course I asked on type911.org. This is where I originally posted the schematic of this module which I traced and drawn last summer. Don't know if anyone here had already done it. I wanted to have a complete understanding of this module operation. Right now the schematic is only hand drawn. Need to find time and skill to draw a cleaner schematic with a drawing tool. So yes the relay I am talking about is one of the two internal relays, the smaller one.

@ Dave, yes, reed relays sometime fail, but mine is ok, I checked it by applying a constant current thru the coil. I slowly raised it up until contacts closed, which was at about 3.5 or 4 amps, so I think it is good. I have spare reed relays anyway. The one I mention is indeed the small mechanical relay, whose coil is shot. So is the coil of the bigger relay. Need to change both. I'll post pictures If I can.

[mysocal911]

Originally Posted by wazzz

@ Dave, yes, reed relays sometime fail, but mine is ok, I checked it by applying a constant current thru the coil. I slowly raised it up until contacts closed, which was at about 3.5 or 4 amps, so I think it is good. I have spare reed relays anyway. The one I mention is indeed the small mechanical relay, whose coil is shot. So is the coil of the bigger relay. Need to change both. I'll post pictures If I can.

There's additional speed sensor circuitry to turn-off the rear blower after a vehicle speed is reached within this relay.
The relay is poorly designed for reliability!

[wazzz]

Originally Posted by mysocal911

There's additional speed sensor circuitry to turn-off the rear blower after a vehicle speed is reached within this relay.
The relay is poorly designed for reliability!

True, as far as I understand it, this circuitry (4538) gets the speed pulses from the speedo and, depending on the car speed (determined by the pulse interval), it will allow or prevent the blower to run, but only when temp switch is triggered (closed). The circuitry alone cannot force the blower on or off if the blower is running in normal heating mode (controlled by levers or button between seats). This behavior is obtained with a set of diodes used as logical ANDs and ORs.
The blower is also temporarily inhibited while cranking.

[mysocal911]

Originally Posted by wazzz

True, as far as I understand it, this circuitry (4538) gets the speed pulses from the speedo and, depending on the car speed (determined by the pulse interval), it will allow or prevent the blower to run, but only when temp switch is triggered (closed). The circuitry alone cannot force the blower on or off if the blower is running in normal heating mode (controlled by levers or button between seats). This behavior is obtained with a set of diodes used as logical ANDs and ORs.
The blower is also temporarily inhibited while cranking.

So once you repair your relay, you'll need to test for that function, right?

[wazzz]

I'll test the heater and be happy if it blows hot air. I may also try to activate the temp switch (simulate an engine overheat situation by grounding the switch input) and see if the main blower comes on when the car is not moving.

[mysocal911]

Originally Posted by wazzz

I'll test the heater and be happy if it blows hot air. I may also try to activate the temp switch (simulate an engine overheat situation by grounding the switch input) and see if the main blower comes on when the car is not moving.

And input the speed signal (pin 1) from the speedo to determine how it affects the rear fan, right?