Carrera - Removing Engine Compartment Heater Blower

[scarceller]

Look at post 82 where I have my schematic.

At the controller pin 3 needs to have 12vdc as this is the feed input for the front blowers. Then when the front blower relay in the controller picks it shorts pin 3 to pin 4 and this pin 4 delivers the 12vdc to the front blowers.

So you can actually unplug the controller from the harness and jumper pin 3 to pin 4 at the harness and with key in 'RUN' you'll have 12vdc at pin3 jumpered over to pin4 if the blowers work up front you have a issue with the controller if they don't work you have a issue with the line feeding pin4 to the blowers.

Originally Posted by krshome

HELP ME!!!!! Ok when I started this Back date back project everything worked fine, I removed engine blower fan and did the mod to the relay. Nothing! No footwell fan at all, so i went back and did the updated mod since I have a 88. Nothing no footwell fan. So I put everything back to stock undid the mod to the relay put the heater fan back in the engine compartment. Now the rear blower works but the footwell blowers do not. I checked for power at the footwell nothing. The rear fan is working in the engine compartment. I checked the fuses at each blower, they are ok. The fuses by the relay are ok. Am I missing any? What did I do to loose all power to the footwell blowers????????

[krshome]

Ok jumped the 3&4 at the harness and the FW fans worked. Cool Thanks. Ok so now here the question, where do I go from here to get it working again?

[scarceller]

Great, that means all the footwell blower stuff is good.

I suspect that the relay inside the controller is not picking. Remove the tin cover and you'll see 2 relays on the board. One (the bigger one) is for the rear blower the smaller one for the front. With the tin removed look to see if/how they pick. If the rear blower is working then that relay is closed. Keep an eye on the other one to see what it's doing. You can even measure the voltage at the relay's coil to see if it is getting 12vdc. Also measure the resistance of the coil to see if maybe the coil burned out?

Originally Posted by krshome

Ok jumped the 3&4 at the harness and the FW fans worked. Cool Thanks. Ok so now here the question, where do I go from here to get it working again?

[krshome]

You know you stuff! The big coil is closing and rear blower is working. The smaller coil is not closing and the FW fans are not coming on. If i push down on the small relays arm to manually close it the fans come on. I measured the coil for resistance and its good. I can't seem to find the spot to test for power but if the jumper work it should be getting power right?

[scarceller]

Correct, if the jumper worked it should be getting power. But if the rear blower is in place and running it should also be getting power.

Could be maybe you damaged some component while messing around with the jumper? Look closely at the area(s) you worked on.

The little relay has a coil, one post is ground the other is 12vdc. It's at these posts you want to see if it has power, should be same posts you measured resistance.

Also, do you have the old or new style relay?

Originally Posted by krshome

You know you stuff! The big coil is closing and rear blower is working. the Smaller coil is not closing and the fans are not coming on. If i push down on the small relays arm to manually close it the fans come on. I measured the coil for resistance and its good. I can't seem to find the spot to test for power but if the jumper work it should be getting power right?

[krshome]

Ok I starting to realize that maybe not everything was in working order to begin with. I never have been able to figure out all the heat leavers switches and knobs, if I got heat I was happy. Well after playing with the jumper on #3 +#4 i realized that the fan speed control for the FW fans never worked but with the jumper it does. Apparently the FW blowers have never worked since I have owned the car. The heat has been coming from the rear heater fan the whole time. I also tested #'s 9, 11,and 12 and I am getting power to the coil in the relay, so something is buggered up in the relay. I think I'm going to go the route of the cheaper relay's hard wired in place of what I have. One question will the aux cooling of the rear fan still work or not?

[aj88cab]

You can test the FW relay coil with a 9v battery. Connect negative to pin 2 on the controller unit. Run the 9v positive to the reed switch post shown in the photo above (post #114). If it operates the contacts the coil is good, if not, well, it's bad and that is the issue (as Sal suggested above).

To answer your question about the aux cooling function...I think that if you use the control unit with the jumper (as shown in post #114) the aux cooling function should work. But...the FW blowers will also come on since the jumper is using the engine blower power directly to operate the FW relay coil.

[krshome]

Originally Posted by aj88cab

You can test the FW relay coil with a 9v battery. Connect negative to pin 2 on the controller unit. Run the 9v positive to the reed switch post shown in the photo above (post #114). If it operates the contacts the coil is good, if not, well, it's bad and that is the issue (as Sal suggested above).

To answer your question about the aux cooling function...I think that if you use the control unit with the jumper (as shown in post #114) the aux cooling function should work. But...the FW blowers will also come on since the jumper is using the engine blower power directly to operate the FW relay coil.

I was down in my basement with a 9V battery testing the coil and heard your post in my email, funny. Looks like the coil is bad. S.O.B.

[scarceller]

For what it's worth, I also went down this path of figuring out the heat controller and in the end I simply removed the expensive controller and replaced it with simple automotive relays.

But here's another crazzy thought: if you don't plan to use the rear blower you could use it's relay to power the front ones. Here's how:
Simply bridge pin #5 to #4 (see my post 82) this will just jumper the rear blower output pin#5 over to the pin#4 output for the front blowers. This will allow you to still resurrect your faulty relay. But if you do this I suggest you also cut pin #10 inside the relay box so that if engine temp rise it won't activate the front blowers.

Crazzy Huuu?

[aj88cab]

Well that sucks...sorry!

Also to add to my comment on the aux cooling function. If you go with Sal's twin relay method you will loose the aux cooling function. The temp sensor that controls that feature is a contact to ground, not sure if it is N/O or N/C...but...I think with a third relay it could be made to retain the aux cooling.

That's your homework assignment for tonight!

[krshome]

I was thinking of using the set up on post #36 with the 1N4001 diode on pin #10 for the engine temp switch. Does anyone know what amp relays to get 30 amp? Also is this the right diode http://www.radioshack.com/product/index.jsp?productId=2036268 ? Thanks Scareller for all the help

[scarceller]

I used 40 Amp relays but the 30 amp will also work. Post #36 is my custom design with 2 relays and if you add the diode and the wiring to pin 10 you also have the Aux cooling feature. And that diode from radio shack is perfect.

[krshome]

Originally Posted by scarceller

I used 40 Amp relays but the 30 amp will also work. Post #36 is my custom design with 2 relays and if you add the diode and the wiring to pin 10 you also have the Aux cooling feature. And that diode from radio shack is perfect.

You Rock!!!!!!!

[westcoast911]

Originally Posted by notmytarga

It's August for Pete's sake - why are we worried about heat???

Here is my question: Does the rear blower run with the levers down , ignition ON but engine not started?

My rear blower was stuck by a chunk of metal in the cage area and now I have it running but the levers don't seem to control it. I can't start the engine because I'm in the middle of a oil cooler/lines install. Will the levers control it once the engine starts? I looked over the Factory wiring diagram for 1975 and didn't see any of the heater control module type stuff - may explain the 'advanced' control.

I have a question along the same lines- car is an 88 Carrera. what switches control what fans? Currently I can only get a fan to come on by using the lever mounted on the dash. The centre dial does nothing, and the big red levers just add heat….are they supposed to start a fan also?

[ChrisP911]

Nice write up.

[Beaky]

Originally Posted by scarceller

UPDATE:

I was cleaning up the rear engine bay and decided to get rid of the heat controller, I replaced it with 2 relays. I wired up sockets for both relays but only installed 1 because I do not have the rear heat blower since I backdated my heat. But I figured to still have the wire harness support running the rear blower in the future.

Here's the final Schematic used for this:


This circuit covers the basics:
1) allows front blowers to run without the rear installed.
2) turns blowers off while in 'START' cranking mode.
3) will turn on only the rear blower if the engine gets hot and the engine temp switch closes.

What it does not do:
1) ignores the speedometer signal, I have NO clue what this was used for. But I think it was part of deciding when to turn on/off the rear blower if engine is very hot.
2) no longer prevents the front blowers from running without the rear.

Wiring this thing up, you have 2 choices:
1) rip apart a stock Heat Controller, take out it's insides and simply keep the plug end and wire the 2 relays and the diode to this plug. This approach will let you do this mod with NO alteration to the stock harness.
2) I did this one: cut the stock harness connector and simply solder and shrink tube the 2 new relay plugs to the stock wiring. This one is more complicated as it's hard to work in that tight space and the stock harness is not very long to begin with.

And YES I have a spare (no longer needed) stock heat controller that is modified to run the front blowers without the rear. I'm willing to sell it if someone wants it, I can easily put it back to stock configuration as well if need be. Check the For Sale section as I have it listed.

Hi folks, great thread. I've recent rebuild my engine to 3.4 nd had the rear fan delete, but want the footwell fans to work to demist the screen - Uk isn't as warm as the US :-). In regards to the Auto relays, will a 40 amp 4 pin work and does it need a diode?
Regards

[scarceller]

You only need to wire up the center relay to run only the front foot blowers. No diode needed and also don't need the relay on the right side of the picture.

[Beaky]

Originally Posted by scarceller

You only need to wire up the center relay to run only the front foot blowers. No diode needed and also don't need the relay on the right side of the picture.

Cheers

[Lyle O]

Originally Posted by aj88cab

This is the updated jumper configuration I helped Tailwinds with a few years back. I did this configuration for a fellow Carrera owner recently and his heat is working fine. FW blowers come on with red levers up and don't run all the time (with levers down) as with other jumper schemes.

Close-up of reed post & pin connection point.


Cheers,
Andrew

I want to thank Andrew and Sal for this series of posts and the thread in general. When I did my heat backdate a while back I did not realize I had the new/updated heater relay control board, so when I did the mod, the footwell blowers were on all the time and I ended up blowing the fuses for the heater controller. Following Andrew’s method here solved the issue completely; footwell blowers come on only when the levers are pulled up, etc. For all future searchers, double check to make sure whether you have the new or old heater relay board layout!

[Beaky]

Having run the bypass relay for several years without issue, recently it worked intermittently and now stopped altogether.

I have good heat, so the flaps are opening, I have checked the fuses which are OK and the footwell fans work if powered directly.

Turning the heat dial does not seem to be engaging the blowers, where and what could be the problem?