Carrera - Removing Engine Compartment Heater Blower

[Talewinds]

The part numbers are the same, but as I discovered before, a quick study of the circuit tracings in this photo versus the circuitry in the photo posted at the beginning of this thread reveals minute differences in the schematic. Simply put, whereas previously the reed switch simply "allows" the footwell blowers to activate, the newer schematic "instructs" the footwell blowers to turn on, this is probably because after a couple years producing this controller in conjunction with the footwell blowers they saw that if engine heated air passed over the footwell blowers and the blowers were not running, it got hot enough to melt the plastic squirrel cage to the housing of the footwell blowers and the change in controller schematics was the simple way to correct this.
Inspect the areas of the controller tracings nearest the footwell blower relay, the schematics are somewhat different, and there are even a couple of differences in the solder locations.
Just today, with the guidance of another helpful Pelican I removed the jumper I had originally placed across the reed switch and moved a jumper from the load side of the reed switch (the load side of the reed switch on this later controller goes directly to the line side of the footwell blower relay coil) to controller connector pin #5. In this new configuration, a small amount of power that goes to the engine blower is rerouted to the footwell blower coil, thus, after the engine blower is removed, the footwell blowers will continue to be operable, but ONLY after the red levers are pulled up.

[scarceller]

Talewinds,

Glad you found a solution! But I still don't fully understand what you did? Partly because I'm not sure how the reed switch in your controller is setup.

In my older controller it works like this:
The large relay for the rear blower is picked/activated the minute you lift the levers (pin 9 and 11 shorted together by the switch on the levers) Once this large relay closes it puts 12V on pin 5&6 but as current flows to the rear blower (via pin 5&6) it passes through the coils in the reed switch (the coils wrapped around the glass tube). Once enough current passes through the coils it causes the switch inside the glass tube to close and this in turn picks the second smaller relay for the front blowers. Once the smaller relay closes it sends power to pin #4 which powers the front blowers via the rotary switch between the seats.

Here is the pin out details:
pins 8&7 have constant 12v and are the input feed to the large relay (rear blower)
pin 3 has constant 12v and is the input feed to the small relay (front blowers)
pins 5&6 are output from the large relay that powers the rear blower
pin 4 is the output from the small relay that powers front blowers
pin 2 is ground
pins 9 & 11 are the signal lines to activate the controller goes to orange levers

then we have 2 special pins:
- pin 10 goes to a temp sensor on the engine and if the engine gets very hot it will cause the controller to command the rear blower on regardless of position of heat levers, the idea here was to move large amounts of air through the heat exchangers to cool them thus cooling the bottom of the engine, trust me this idea really works! Even if the levers are down the heat simply dumped out the heat valves at the top of the transmission, many folks in hot climates set the switch on the heat levers so it closes if you slightly lift up on the levers this causes the rear blower to run and thus keeps the exchangers cool all the time.

- pin 1 this is the mystery pin, it is the speed signal from the speedometer the same signal that feeds the cruise controller. I have no idea why the controller needs to know about vehicle speed but my guess is that it has to do with pin
#10 and maybe they turn off (or on) the rear blower at some certain vehicle speed. I never could exactly figure this pin out because it goes into solid state chips that have no part numbers.

Here's the rough schematic for the controller:


Then here is my circuit for replacing controller with relays, it is useful because it has all the input pins described:


I would like to really understand your controller and how that reed switch is wired and also exactly what you jumpered.

Thanks.

[scarceller]

Talewinds,

After re-reading what you wrote a few times I think I got it: so in your controller pins 5&6 are the output pins from the large relay that feed the rear blower and you are saying that this same signal from pins 5&6 is feed to the coil of the small relay? if this is the case then the small relay (front blowers) will always put out 12v on pin #4 the minute the large relay picks. If so then my question is what does the reed switch output from the glass tube power?

[scarceller]

OK, I see the difference here's a picture:

[Buffjamr]

Just completed this. I had the same result. This is definitely the way to jumper for Carrera's with the modified/updated controller.

I replaced the rear heater motor(Wavey mod) and did the controller mod and now have the best of both worlds. I went from no heat to a Sauna in an afternoon.

BTW got the motor at Oreilly (Siemens PM351) works like a champ and has a warranty.

[pplkook]

Sorry to revive this again. After doing a heater backdate on my 85, I am starting to figure out how to make the foot well blowers.

From what I can tell, I have the following options if I want to retain the use of the foot well blowers minus the engine compartment electric blower.

1. If I have the "old" relay, I can do the multiple relay upgrade in earlier posts, can be done with one relay if required
2. If I have the "new" relay, I can follow Talewinds jumper instructions (anyone have a pic)

Will 1 and/or 2 address the functionality of passing more air through the HEs if the engine bay is hot?

Does this sum it up?

Thanks in advance

Jack

[scarceller]

You have a few choices:

1 - The simple fix is to just jumper the reed switch as in the pictures above.
2 - Replace the entire heat controller with 1 simple relay. (I did this in my car) see post few posts up, I posted the wiring. I like this setup because it uses simple cheap SPDT 30 or 40 amp relay. Someone else in this thread also did this mod by gutting a bad Controller and wiring a simple relay to it, this way he could keep the current stock wire harness. I cut my harness and soldered in the new relay plugs directly to the stock wires.

If you remove the rear blower you can NOT force as much cool air through the heat exchangers. You give this up by removing the rear blower. But you still always have some air flow through the exchangers from the engine fan with the backdated heat configuration in the engine bay. If I lived in a very hot climate I would not remove the rear blower.

BTW - I have my old controller listed FS on this sit, it's already modified and ready to go. I don't need it any more and never will.

Originally Posted by pplkook

Sorry to revive this again. After doing a heater backdate on my 85, I am starting to figure out how to make the foot well blowers.

From what I can tell, I have the following options if I want to retain the use of the foot well blowers minus the engine compartment electric blower.

1. If I have the "old" relay, I can do the multiple relay upgrade in earlier posts, can be done with one relay if required
2. If I have the "new" relay, I can follow Talewinds jumper instructions (anyone have a pic)

Will 1 and/or 2 address the functionality of passing more air through the HEs if the engine bay is hot?

Does this sum it up?

Thanks in advance

Jack

[JPaul]

I'm assuming I can build scarceller's 1 or 2 relay circuit using a 4 lug automotive relay box where lug 30 is normally open?

What a god-send this is for $20 and a couple of hours. I went to look for a replacement box and wasn't surprised but still flabbergasted. They're as much as a rebuilt DME. A lot of engineering for not much return.

Smart and simple does the trick. Awesome work, Sal!

[scarceller]

JPaul,

Yes just use 2 simple automotive relays and follow my schematic. If you don't use/have the rear blower then you only need one relay. In my car I removed the old controller and then cut the harness and wired in 2 relay sockets in place of the old harness connector. But others have also gutted the stock controller and wired the new relays to the stock controller can. This allows you to keep the stock harness as-is.

But before you go this route: are you certain the controller is bad? I suggest you follow my schematic and test each pin at the stock harness for voltage and grounds. Pay very close attention to pin #9 as this one is often problematic, this pin gets grounded when you pull up on the heat levers between the seats and if it does not go to ground the controller will not come on. The other typical problem is the rear blower, if the blower is not working or removed then the controller will not come on as well. I suggest you apply 12vdc directly to the rear blower to be sure it works.

Good luck.

Originally Posted by JPaul

I'm assuming I can build scarceller's 1 or 2 relay circuit using a 4 lug automotive relay box where lug 30 is normally open?

What a god-send this is for $20 and a couple of hours. I went to look for a replacement box and wasn't surprised but still flabbergasted. They're as much as a rebuilt DME. A lot of engineering for not much return.

Smart and simple does the trick. Awesome work, Sal!

[nesslar]

This should be easy:
How does the rear blower "remove excess heat" and thereby help to cool the engine when the engine electronics sense that is necessary? Or does it actually do so? If so, then there is a route for heat exchanger air to escape (and obviously it ain't going into the cabin?).
There must be a path for the air flow in the "hot" engine situation that I've read about in this thread. I am not aware of it. Where does that hot air go? Dumped into the path of the engine fan somehow? Thanks.

[Canada Kev]

I suspect the air is run through the heat exchangers, cooling the exhaust a bit? Any excess air/heat would be dumped out of the system at the heat flapper boxes instead of continuing into the cabin.

[scarceller]

If you look at schematic above you'll see pin #10. This pin is attached to a thermal switch on the engine and when very hot condition is detected it grounds pin #10. Once this happens the relay commands the rear blower on (even with no call for heat). This usually happens in the hot Summer and you'll most likely have the heat levers down, if the levers are down the the heater flapper boxes simply dump the hot air under the car and not into the cabin. The idea is that the rear Blower comes on and feeds cool air through the heat exchangers that are very hot, this cool air helps cool the exhaust headers and the air is then dumped beneath the car just forward of the Transmission. Simply if the engine gets hot enough the rear blower comes on and this helps cool the the exhaust components.

Originally Posted by nesslar

This should be easy:
How does the rear blower "remove excess heat" and thereby help to cool the engine when the engine electronics sense that is necessary? Or does it actually do so? If so, then there is a route for heat exchanger air to escape (and obviously it ain't going into the cabin?).
There must be a path for the air flow in the "hot" engine situation that I've read about in this thread. I am not aware of it. Where does that hot air go? Dumped into the path of the engine fan somehow? Thanks.

[nesslar]

Thanks all. I am not familiar with the "flapper boxes", though I reckon I should be; will look into those (Bentley) just to satisfy my curiosity.
The heat "valves/flappers" are simply "forced open" by the air pressure, since the air is not going through the rear blower and ducts, I assume.

[Canada Kev]

The flappers are just a circular shaped piece that fits in the air duct (flapper box). They pivot around a central point like a throttle and are connected directly to the heater levers or in the case of auto heat, the servos.

Lift your heat lever and the flapper opens allowing hot air into the cabin. Otherwise any warm air gets dumped outside underneath the car. That's why, if you store your car for the winter, it's suggested to turn your heat on to discourage little critters from getting into your heat exchangers through the open flapper.

[aj88cab]

I thought I would expand on the "modified mod" that Tailwinds discusses above (post #81). I think I am the "friendly Pelican" he mentions

The problem begins with the diagram that is shown in post #82. It has been around forever, but it is wrong. The correct diagram is this:



Pin 12 is the footwell relay coil power supply and it is hot whenever the ignition is ON. So the previous jumper mod, that bypasses the reed switch, energizes the coil (closes the FW blower contact) all the time.

Pin 12 also provides the power for the IC chip in the controller unit so in order for some of the additional functions provided by this controller to work (see below) it must have power even when all the blower controls are OFF.

This was the new mod that Tailwinds and I discussed:



This draws power directly off the engine comparment heater blower circuit to energizes the FW relay coil. So the red levers now control the FW blower relay directly, without the reed switch in the circuit. As noted you can cut the reed switch out of the circuit or just leave it, but it's probably better to take it out of the circuit all together. There are a couple of locations to pickup the jumper... right off the pins (5 or 6) or on the circuit board side.

This should work with or without the engine blower installed.

Some additional items that were mentioned above:

As mentioned above, the blower temp switch (pin 10) turns on the engine blower to provide auxillary cooling if things get too hot, like when stuck in traffic or idling. I am not sure if this functions after the car is off like some modern cars. This temp sensor is located on the oil breather on top of the engine. BTW - I have never seen this function occur in my car.

The speedo input (pin1) disables the blower temp feature above a certain speed (assuming I guess that the cooling fan will do its job if the car is moving and RPMs are up).

I believe the reed switch along with some logic in the IC chip is in the circuit so this auxillary cooling function (engine blower) can happen without the footwell blowers coming on regardless of the FW speed dial setting.

Hope that helps.
Andrew

[JPaul]

Sal,

Once I got the engine compartment fan going again, the footwell fans quit working. Suspecting the reed switch, I pried the cover of the control box and found a damaged ceramic daughter board. I think I may have cracked it while trying to pry the cover off. Traces are too small to reassemble the pieces so I scrapped it and went for replacing with your circuit, which I completed this morning.

I can't tell what's working and what isn't at this point. The footwells are emitting significant heat but they don't come on with the ignition energized and I can't tell what's happening once the engine is started. when I pull the on/off levers I'm pretty sure it's the engine fan generating the warm air flow at this point. My zero to 3 switch has no effect at all (which was the case when I did the PPI on the car a couple of years ago). I suspect this switch is faulty but will now start the process of diagnosing as you've detailed in earlier posts.

I normally enjoy the process of fixing things but my patience is wearing a bit thin on this project.

[scarceller]

Go back to my post 82 and print that diagram to use to debug your issues.

Then test the following, do these tests in order do not skip any steps:
- measure across pin 2 (ground) and pins 7,8and3 you should measure 12vdc even with key off. So pin 2 is ground and 7,8and 3 must have 12vdc at all times.
- Then pin 12 has 12vdc with key in 'Run', simply measure across 2 (ground) and pin 12 then turn key to run and you should have 12vdc
- Next we'll test the switch on the red heat levers between the seats. For this you will first measure across pin 11 to 7 you should read 12vdc if you do not this means pin 11 is not getting ground and needs more debug to figure out why.
If 11 to 7 reads 12vdc now measure across pin 9 to 7 and with heat levers pulled up you should read 12vdc with the levers down you read 0vdc.
- Next with all relays removed simply jumper pin 7 (12vdc) to pin 5 this should instantly activate the rear blower.
- Now jumper pin 3 to pin 4 this will send power up to the front footwell blowers and if you then rotate the rotary switch between the seats you should hear the footwell blowers come on.

Run each test above in order and see which test fails, once you hit a failed step report back so we can track down the failure.

The tests are in progressive order to:
- test the ground and power lines
- test switch on heat levers
- test rear blower lines
- test front blower lines

If you really look at the picture I posted in post 82 you will see that we are simply testing at the relay harness in the engine bay, all tests are done at that harness plug. You don't need to run the engine for any of these tests so it will be very easy to know if blowers are running or not. You can use a Voltmeter or a simple 12vdc test light for all these tests.

Hope this helps.

Originally Posted by JPaul

Sal,

Once I got the engine compartment fan going again, the footwell fans quit working. Suspecting the reed switch, I pried the cover of the control box and found a damaged ceramic daughter board. I think I may have cracked it while trying to pry the cover off. Traces are too small to reassemble the pieces so I scrapped it and went for replacing with your circuit, which I completed this morning.

I can't tell what's working and what isn't at this point. The footwells are emitting significant heat but they don't come on with the ignition energized and I can't tell what's happening once the engine is started. when I pull the on/off levers I'm pretty sure it's the engine fan generating the warm air flow at this point. My zero to 3 switch has no effect at all (which was the case when I did the PPI on the car a couple of years ago). I suspect this switch is faulty but will now start the process of diagnosing as you've detailed in earlier posts.

I normally enjoy the process of fixing things but my patience is wearing a bit thin on this project.

[shadowjack1]

This is my first post. I just replace my 79 911 SC that I lost in Hurricane Katrina with an 88 Carrera. Its good to be back in a Porsche.

This was a good read. More information then a double E can handle. Maybe one you guys can help me figure this one out. My rear fan blower motor get 12 v, (11.97v) but will not run, however when i hook the fan direct to the bat. the fan runs great. With the engine running, pull up on the two levers in the pass. compartment, nothing either.
If the foot well fans are not working will this also make the rear fan not work.
Thanks
Bill

[scarceller]

Other way around: if the rear fan does not work (draw current) then the fronts won't work.

Look carefully at the schematic in this thread. If as you say you have 12vdc across the 2 pins in the harness to the rear fan the fan should run. If it does not I suspect a bad ground somewhere.

Originally Posted by shadowjack1

This is my first post. I just replace my 79 911 SC that I lost in Hurricane Katrina with an 88 Carrera. Its good to be back in a Porsche.

This was a good read. More information then a double E can handle. Maybe one you guys can help me figure this one out. My rear fan blower motor get 12 v, (11.97v) but will not run, however when i hook the fan direct to the bat. the fan runs great. With the engine running, pull up on the two levers in the pass. compartment, nothing either.
If the foot well fans are not working will this also make the rear fan not work.
Thanks
Bill

[shadowjack1]

Yes I do get 12 v (11.85 v now) I'm thinking that the relay is faulty and not sending enough voltage to run the motor. If I had a bad ground, the plug at the fan would not see 12v.
440 volts I get, this 12 volt stuff is ??????

Bill