Manual heater console/switch not working. Please help...

[Mauricio911]

Hi, My manual heater console/switch is not working. Sometimes if I move the dial between positions 1 and 2 I can hear a fan fire up. Which would tell me that the switch/dial itself might be the problem. The foot blowers do work when I pull on the red levers. are there any serviceable parts in the console? I checked on the pelican site and I did not find any parts for the console. Does anyone know if the blower relay could cause this? Suggestions will be greatly appreciated.

[fuelie600]

Mauricio,

There is a switch on each lever. When you pull one or both levers up, the rear blower motor should come on. The footwell motors will also come on if the rotary switch is set to anything other than zero. The rotary switch controls the footwell motors. 0 is off, 1,2,3 are low, med, high.

I had to change the fuses on my foot well blowers and clean carpet fuzz out out of the lever switches to get everything working right.

[aj88cab]

This link is a good description of the control circuit for the mystery of this heater system. As you will see it is not as simple as you might think. Maybe it will help trouble shooting.

Heater Controls

Good luck
Andrew

[Mauricio911]

Thanks for the feedback.

My concern is that the rotary switch normally does not seem to make any difference. If it is on zero and I pull on any of the levers the footwell motors come on. The rotary switch does not seem to control any of the footwell fan speeds. Sometimes it does fire up what it sounds like an additional fan in the dash.
Could this point to the relay in the engine compartment then?

[aj88cab]

The "0" setting on the rotary dial is not really off. "0" and "1" are the same (slow) speed (explained in more detal in the link above). The dial only controls the footwell blowers speed, the engine blower is on or off only by the levers. If the dial does not control the footwell blower speeds it could be the dial switch, the relay, or maybe even the fan speed resistor. It is also possible that a PO by-passed the fan speed resistors.

You can remove the center console and see if the rotory switch contacts are working properly. You can check the relay by trying a know good one (they aren't cheap, so you need a fellow P-car owner to swap or a friendly shop for this).

The "3" setting runs through a relay on the front trunk fuse/relay panel.

Is the "additional fan" perhaps one of the footwell blowers that is binding up at slow speed and coming on at the higher setting? The levers and dial do not control anything other than the engine blower and footwell blowers so I don't think it could be the fresh air fan.

Andrew

[Mauricio911]

Thanks Andrew that helped. I took the rotary dial out, lubricated it and now it works for positions 0,1 and 2. Which is much better than before.

I will take a look at the relay in the front trunk. Hopefully it will be as simple as replacing that relay in order to fix position 3

Thanks again.

[aj88cab]

If position 3 is not working then there is a good chance it is the relay in the front or a fuse in the back on the engine compartment fuse block. The front relay is one of the typical round plug-in units so you should be able to swap it with another to test.

Good luck
Andrew

[fuelie600]

BTW, does anyone use position 3 for more than a few seconds? I rarely use my footwell blowers cause it gets too damn hot in the car!

The engine blower is all I ever seem to use....

[aj88cab]

Evan,

You make a good point. To illustrate just how hot it can get, when I bought my Carrera the PO (or somebody) had removed the inline fuses. When I replaced the fuses they kept blowing. Thinking I needed new motors I took the fans apart and found that over time the heat had caused the plastic fan cage and the plastic fan housing to fuse together - no motion, instant blown fuses. I cut/pryed them apart with a putty knife. They have worked since but do tend to screech occationally when its real cold. I guess this might be one reason that there is no real OFF setting for the footwell blowers - for fear of them melting Hot indeed.

You can try controlling the amount of heat by just pulling up the levers partially if you have manual controls. The high speed position 3 does come in handy when its de-frost time though.

Andrew

[Mauricio911]

So it is not the fuse in the trunk. At position 2, pin 87 on the relay gets about 8 volts. Yet at position 3, pin 87 gets nothing. I swaped the relay with a couple other ones and got the same result.

Also checked the fuses on the engine compartment.

Could it be the resistor then? Where is the resistor anyhow? Any ideas?

[aj88cab]

It sounds like the relay is operating. When in positions 0,1, or 2 pin 87 will get voltage from the resistors, 8v confims that, but the internal contact of the relay is open, the voltage comes from the load side of the relay (the resistors). Voltage should vary between positions 1 & 2. In position 3, the relay closes (pin 30 to pin 87) and takes the resistors out of the circuit and provides full voltage (and 25 amps) for full speed operation.

Check the pin 30 socket it should be 12v (always hot). If not then you have a break between the socket and the fuse. This 25A fuse is only used for high speed.

If you have access to a Bentley manual there is a good diagram of this circuit.

Andrew

[Mauricio911]

Pin 30 is fine. Always hot. That would leave pin 85. Isn't 85 supposed to be ground on position 3? Because right now it is always hot.

Given that pin 85 comes from the rear engine relay. Does that mean that the rear engine relay is the problem?

[aj88cab]

I think your probably right about the rear engine relay. The Bentley wiring diagram is for auto-heat controls, so it is a little vague about what pins go where for manual controls. But pin 85 I believe should be ground like you said. Being hot is a bit confusing, but the rear relay is more of a control unit than just a relay. It is a PCB with 3 integral relays and a bit of electronics. So a bad diode or something could be the culprit, that might explain the 12v on the ground leg, but I'm not an electrical engineer.

Those little boxes are not cheap by the way.

If anybody out there has a wiring diagram for the manual controls and/or an schematic for the control unit/rely it would be great. (OK, maybe I'm dreaming about the schematic, but it always amazes me what folks have on this forum, and it never hurts to ask)

good luck
Andrew

[imcarthur]

Originally posted by Mauricio911
Where is the resistor anyhow? Any ideas?

Resistor for footwells is in the trunk - left side - against the firewall. But if you have the lower speeds, it sounds like it is working.

Ian

[Mysterytrain]

Not sure about the location of things on an 87...But on the SC's the relay in the engine compartment is for the heater blower that lives back there. I think the relay that provides power for position 3 on the switch is located in the trunk behind the dash. When you turn the dial to position 3 your are sending 12 volts up to pin 86 on the relay and thru the relay coil and to ground on pin 85. This activates the realy and sends power that is sitting on pin 30 out thru pin 87 to the blowers. Once you locate the secret hiding place for the relay look for 12 volts at pin 86 [with the ignition on]. Check for power on pin 30. Check the ground connection on 85. If all that looks good swap the relay out. He is a drawing of the harness to help to track down the relay. Note that the relay is part number 13 and is connected to the socket [12] that lives on the end of its own little harness. That harness has a wire with a terminal connection which is most likely the ground. I'm guessing that the other loose wire shown is power going to pin 30. This leaves the two wires in the harness as the control wire [12 volts from position 3] to activate the relay and the switched 12 volts from pin 87 to run the blowers at full power.

also note that the tubular part with 3 wires coming off of it between 10 and 11 is the speed control resistor for positions 0,1 & 2. Hope this helps some.

[Mauricio911]

I found an schematic from another post on this site
http://www.type-911.co.uk/images/exhausts/heatingtech5.jpg
BTW, you can view the other pages of that article by changing the 5 with a 1 through 6

Am I gathering correctly from it that simply I could check pin 4 on the Engine comparment controller and it should be ground when the rotary dial is at 3?

Also, Ron pin 86 is fine as well. It is always hot.

[aj88cab]

Nice find on the article/diagram link. I believe you are correct regarding pin 4 being ground in position 3.

Andrew

[acapella8]

Considering I have no heat in my 78SC yet, this is GREAT information, I'm posting here so as to bookmark the thread.

[Mysterytrain]

Man, I hope I'm not confusing the issue here. In my earlier post there is an exploded drawing of a version of a footwell blower assembly with the 'dumb' console that I think you have. That type of console doesn't have all the circuits and sensor monitoring that the 'smarter' automatic heater console has. The drawing might also include some features that you don't have but I posted it so that you would at least have some idea as to where to look for the relay. Systems with footwell blowers have a second relay and ceramic resistor in the front of the car that are used for controling the blowers. The methods of activating differ slightly from year to year but basically with a manual system when you turn the dial to any of the speed positions 0,1,2,or 3..nothing should happen, that is until you pull up on the red heater levers. This operation activates the footwell blower circuit and of course opens the heater valves allowing hot air from the heat exchangers to flow into the cabin. The following diagram from another pelican head might help to clarify how this is happening and help aid in your troubleshooting:


If you look at the drawing you will see an area labeled "Engine Compartment Controller". That device can be a printed circuit in a black box or something as simple as a relay. At any rate, when you call for heat by pulling up the red levers that 'controller' sends voltage to the heat control switch for the heater blowers. The power is sent from the wiper of the switch thru positions 1 or 2 and then on to the resistor assembly. The more resistance the slower the motors spin. In this example you will also note that there is no connection and position 0 [off]. The change to ' no off' in the circuit came later along with inline fusing of the motors. Now, if you move the switch to the number 3 position you provide a ground connection thru the footwell blower relay coil {the relay in the front of the car!}. Note, that the 12 volts to pin 86 of the relay is also provided by the 'engine compartment controller' . This activates the relay and sends the full 12 volts sitting on pin 30 to the blowers. Why did the factory do this? Well, at full voltage the motors are pulling a bunch of current so the relay protects the contacts on the cheapo speed switch from cooking itself...same reason we install relays on our headlights!
Back to your problem...it sounds like the "engine compartment controller' or relay is working just fine because it is allowing the blowers to operate in the 2 slow speed modes when the levers are lifted. So, this kinda points to the relay in the front of the car that is used for the number 3 position only. That relay harness in the first picture might be unpluged. The relay might be bad or not in place. The fuse feeding pin 30 might be blown [up front in the luggage compartment] or the ground connection might be broken. Let us know how this turns out and where the relay is located. Some pictures would be great.
Forgot to ask this..do you still have a heater blower in the engine bay?
Oh, one other thing if the circuit has been modified by the last owner then all bets are off..the best you can do is to draw a diagram of what you have and try to figure out what they was thinking.

[aj88cab]

Originally posted by Mauricio911

Am I gathering correctly from it that simply I could check pin 4 on the Engine comparment controller and it should be ground when the rotary dial is at 3?

After further study and refering to the numbering in the diagram at the link you found, I believe it would be pin 2 on the engine compartment controller that is ground. This would show-up as ground on connection point 4 on the passenger compartment console (this is at a connector in the console). This appears to be a dedicated ground path for the #3 high speed setting.

So you might want to check continuity from pin 85 (front relay) to position 4 connector (console), then with switch at setting 3 check from connector position 4 to position 2 (this checks the actual switch), then from position 2 to ground. The specific ground point according to Bentley is "#G302 - ground strap at right front transmission mount." Seems like an odd place to ground the system but.........

Andrew