Pulled engine heater blower, now footwell blowers won't work!

Colby · 03-17-2002, 06:42 PM

I plugged in the engine blower and sure enough, the footwell blowers came to life. It seems this needs to be plugged in or the other blowers won't work. How can I get around this? I was thinking of measuring the resistance of the engine blower and splicing a resistor in its place to "fool" whatever and allow the other two to work. But if there is an easier way, I'd love to know!

Colby

Argo · 03-17-2002, 08:36 PM

In the Bentley manual for my '88 there is an "additional blower relay" shown which appears to be the way power is brought to the footwell blowers through closing of a circuit by the rear blower motor. It appears to be located up front in the luggage trunk. There might be a way to manipulate this relay to accomplish what you want, but I am definitely no electrical expert so manipulating it might just be a way to start a nice electrical fire. Might be worth looking into, tho. I don't know what year your car is so your wiring might be different.

BTW, what are you trying to accomplish? I'm a little curious ...

Argo
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Colby · 03-17-2002, 08:41 PM

I converted over to early style heat exchangers. I rigged up a way where I could still use my Carrera heating system w/ them last summer. Now, I am planning to turbocharge my car and needed the room for an intercooler. So I completely backdated my heating system (ran tubes off heat ducts right off the side of the fan). This eliminates the engine blower. I still have the footwell blowers, so I figure they will provide enough heat that the engine blower was unnecessary. But now I don't have any blowers...not good. Ok, I will look into that relay. Anyone else have an opinion on this?

Colby

Colby · 03-17-2002, 10:05 PM

Ok, I looked into that and you're right. The 85 (white/grn) and 86 (black) wires come from the heater control unit. When they tell they relay the engine blower is on, they switch the relay so power from 30 (red) goes to 87 (white/green) which sends power to the auxillary heaters. So I tried putting a jumper between 30 and 87 so my auxillary blowers will always get power. And this worked but....

my auxillary blowers ALWAYS had power. I couldn't turn them off, or adjust them w/ the switch. So I need to look further back in the system. I need to find some way to trick the heater control unit (the knob which controls the heaters) to thinking the engine blower is on. Judging by the schematics, it looks like the heat control engine relay sends power to the heater control unit via a yellow wire. So I need to confirm that the yellow wire to the heater control unit shows +12v when the engine blower is wired up and on, and shows no voltage when its off or disconnected. If this is the case, I will just hook a constant 12v source to the yellow wire and I'll be good to go!

Colby

Argo · 03-18-2002, 06:25 AM

Yup, that's along the lines of what I was thinking of - wire the red (30) and 87 (white/green) permanently together at the relay and then, further "downstream" wire a switch into that circuit (along with an appropriately sized fuse!). This should give you fans when the switch is turned on. You could use the 4 position (0,1,2,3) rotary switch to do this (if that's what you have) but I have read from several people on this board that the "0" position on this switch is not really "off"; the "0" and "1" positions hook up to the same circuit so that the footwell blowers are always on at least at the minimum speed when the rear blower is operational. If I remember correctly, I tested this when I was messing with my footwell blowers and found it to be true. Maybe you could tap into the circuit for the heating levers so that only a footwell blower (instead of the rear blower motor) would come on when it's corresponding lever was raised . You'd have to be careful that the switch could carry the current without overheating. Again, I'm no electrical expert but it seems like there is a solution here somewhere ...

Argo
88 Targa

Colby · 03-18-2002, 03:46 PM

What about just splicing in a resistor in place of the engine blower? That way, everything works as usual.

Colby

Argo · 03-18-2002, 07:42 PM

I was thinking about a way to jump the relay and cut into the footwell blower circuits (they're already fused) and connect them to the heat levers but, after thinking some more I agree with you. Installing a resistor would be the most elegant, simple and easily reversible solution. I don't remember seeing any info about resistance levels on the motor or housing when I had mine apart. A multimeter could tell you easily enough or, as a back-up, you could take the motor to an alternator repair shop and I'm sure they could tell you (as well as selling you the proper resistor and ideas on how to wire it in). If you could find another connector that mates up with the one that plugs into the blower motor (brown and yellow wires?), you could wire in the resistor without cutting any wires at all - just plug it in as needed.

But, now as I think about it, who would ever want to replace an intercooler with the heater blower motor?

Argo
88 Targa

dickster · 03-19-2002, 06:15 AM

thought this might be useful:

http://www.type-911.co.uk/exhaustparts.htm

look for :

Problems with your Heating System on pre 1989 911's? Check This Out!!! Page 1
Problems with your Heating System on per 1989 911's? Check This Out!!! Page 2
Problems with your Heating System on per 1989 911's? Check This Out!!! Page 3
Problems with your Heating System on pre 1989 911's? Check This Out!!! Page 4
Problems with your Heating System on pre 1989 911's? Check This Out!!! Page 5
Problems with your Heating System on pre 1989 911's? Check This Out!!! Page 6

i found it on another thread - v good

Colby · 03-19-2002, 08:59 AM

Yep, read all those. They help explain how it works, but not what I need to do to bypass it. I took the engine blower to an electric shop today. 1 ohm resistance. They gave me a 1ohm, 5 watt resistor, told me to try it and see how it works. If it gets hot, I'll need to go to a higher wattage resistor (but they can't imagine it being over 5 watts). I also bought some spade connectors that fit in the plug perfectly. I will try it tonight and let you know how it goes (and if my car catches fire....hehehe).

Colby

Argo · 03-19-2002, 09:59 AM

Sounds like you have it solved. My only concern was about the heat generated by the resistor but it sounds like that won't be a problem. I suppose you could install a small cooling fan for the resistor; just tap into the circuit for the ....

Just kidding.

Argo
88 Targa

Colby · 03-19-2002, 04:47 PM

Welp, it worked....for about 20 seconds. Then the resistor overheated and burned up. Guess there's more than 5 watts going through there. Next up...10 watts. Then 15, then 20... I WILL SOLVE THIS!

Colby

Argo · 03-19-2002, 07:24 PM

Bummer. Hopefully a larger resistor will solve the heat problem. When the resistor starts getting as large as the blower motor it's replacing, I'll start fleshing out my footwell blower circuit/heat lever idea.

I wonder if a cool collar would work ........

Argo
88 Targa

Colby · 03-19-2002, 07:47 PM

Yeah, if I can't find a resistor that will work then I am going to try to find a way to wire the 1,2,3 knob (for lack of a better name) and the footwell blowers independently of the blower in the engine. I hope not to do that (I really don't want to start rewiring the car), but if I have to...

Colby

Argo · 03-20-2002, 07:09 AM

I was thinking of jumping the relay up front to keep the footwell blowers on all the time and then cutting into the footwell blower circuit right by each blower motor; they're already fused (with an in-line fuse) right by the motor and you'd just have to run a short wire under the dash, then under the carpet back to either the 3 way switch or the levers. Be careful of using the 3 way switch - I'm pretty sure that the "0" position is not really off - it is tied into the same circuit for the "1" setting so the footwell blowers are always on if the rear blower is on - even if the 3 way switch is turned to "0". You can check this easily enough - just jumper the front relay like you have then turn the 3 way switch to "0" and see if the aux motors stop or remain on the low speed. You might have to remove the cardboard backed /carpet covered kickpanel covering the aux blower area to make sure you can hear if they stop or not - they're pretty quiet running on the low setting. The only other thing to check is whether the rotary or heat lever switches are robust enough to handle the continuous current running the motors without overheating.

I just did a search for thread that maintained that the "0" position did nothing and finally found it: http://www.pelicanparts.com/cgi-bin/vb/showthread.php?s=&threadid=33962&highlight=heater+switch

Argo
88 Targa

Colby · 03-20-2002, 05:50 PM

Ok, with a 25 watt, 1 ohm resistor it did not burn up but got VERY hot and started smoking (the resistor). This was the largest resistor they carried, so I am going to Plan B. The engine blower relay (in the back driver side, behind the black plastic) sends a signal to the heater control unit (the 1,2,3 knob I believe) whenever the engine blower is on. Without this signal, the front blowers won't work. I believe its one of the two yellow wires. I am going to use a test light and find the wire that shows voltage only when the levers are pulled up and the engine blower is plugged in. I will then unplug the engine blower to confirm the voltage to this wire disappears. I will then tap this wire into a fused power source (probably ignition, so it cant come on when the car is off). This way the switch will always think the engine blower is on and allow me to use the aux fans at will. I read that thread and I got the impression it meant that at 0 and 1 the fans are always off, and at 2 and 3, they turn on. If this is true, GREAT! On 0 or 1 the fans will be completely off. When I need them, I pull the levers up (just to allow the flow of hot air, not necessary for them to work) and turn the knob to 2 or 3. I will try this either tonight or tomorrow and let you know how it goes.

Colby

Argo · 06:53 PM

If I'm following you correctly, that should work ok. I'm curious about the 0123 switch now. I remember when I read that thread thinking how goofy Porsche engineering could be to bother putting a specific setting on the rotary switch that intentionally did not do what it was supposed to (turn footwell blower off). It was so odd that I looked into it when I was messing with my footwell blowers last year and I'm almost positive that the 0 setting was the same as the 1 - the motor ran slowly at both settings. I believe I even checked it by pulling that in-line fuse to verify that the motor was running at both 0 and 1. But, that was a while ago and I've solved a few other electrical glitches since then so I can't swear to it. I'll be interested to see what you find on yours. Maybe the switch wiring was changed for the later 80's models. No matter, if you can't use the rotary switch it 's no big deal to get another switch and mount it wherever it's convenient.

Isn't this the way it always works - you're going to spend more time and effort solving this tangential problem than you will installing the turbo and intercooler.....

Argo
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john walker's workshop · 03-20-2002, 07:06 PM

how about a ceramic ballast resistor from the auto parts store. all resistors get somewhat warm. even a light bulb would probably work.

Colby · 03-20-2002, 07:58 PM

Ceramic ballast resistor???? What's that? I'm willing to try anything at this point...

The 25 watt resistor I used didn't just get warm, it was smoking! Not good.

A light bulb. Interesting idea. I'll try it just for grins to see what it does (like explode in my face...hehe).

Colby

john walker's workshop · 03-21-2002, 07:08 AM

a ballast resistor is used on older cars to keep the points from getting the full 12V and burning. they're heavy duty. most parts stores have a variety of them. the one for a 57 chev has a mounting bracket. being that the relay switches full 12V power to the fans, i'm pretty sure the voltage drop before the relay shouldn't affect anything.

Tim Polzin · 03-21-2002, 08:37 AM

Ohm's law would give you 12 amps current draw with a 1 ohm resister at 12 volts. 12 amps at 12 volts is 144 watts.
Tim