Heater Fan Switch

DocHornet

A few weeks ago, while tidying up the wiring underneath the dash, I noted the P.O. had cut the power wire to the heater switch, it was just dangling there. I ran a 10 gauge wire from my new fuse panel (powered straight from the battery via switched relay) to the heater switch.

Today, I had the first opportunity to inaugurate the heater system. The switch seemed to only work in the full-on HIGH position, and I'll say that fan was definitely turning... sounded like a hurricane.

However, after about 30 minutes of operation, I touched the heater switch, and that baby was hotter than a firecracker. Feeling under the dash, the wiring to/from the switch was not all that hot, so I suppose the heat comes from the 60 year old resistance mechanism in the switch.

Wondering if anyone else has experienced the same problem, and if anyone knows of a source for a new heater switch?
Thanks
Phil,
Austin

[Deleted User]

Those were a high failure item as you might guess. Most folks did just what you found. Cut the wire open the cowl vent to feed the heaterand off you go. By the way if you read the manual that was the intent. The blower motor was refered to as the defrost motor I think. I checked my stock I don't have any good used ones,
Roger

onerare39

The two speed fan switch in the dash in my 54 gets really warm when it's turned on either speed.

John

RonS

Mine has been like that for years, ie, operates only on the first position(high). Power will go into the switch on low, but not enough voltage will pass to the motor. I would think that the reostat is bad. Does any one repair these? I think I look into messing around with it.I frankly use it once or so per year, so it was never too much of a concern to remind me to fix it.

Unknown

If you have the switch out and look at the back of it the first thing you see is that the body is made out of ceramic, the second thing is a small coil of heavy wire snuggeled down in it. The coil of wire is a resistor that drops the voltage to the motor down for low speed. that resistor gets red hot when it's switched into the circuit, the heat transfers into the switch and after 60 or so years the contacts get oxidized. If you've ever repaired a headlamp switch for one of these cars you've seen the same thing in them. If you feel confident doing it, you can take the switch apart and clean the contacts and give them a little more tension. Probably go another 50 to 60 years. The higher resistance in the contacts causes the excessive heat in the switch, altho they do run kinda warm.

DocHornet

Thanks for all those comments. It dawned on me that the 12V system in my car may be contributing to the problem... don't know how the additional voltage affects that resistive speed control, and I guess the extra voltage explains why that motor runs like a jet engine.

I'm considering replacing the heater switch with a Pulse Width Modulation circuit. I did this on a Porsche 911 I owned, replacing a 3-position switch including a huge resistor, with this continuously variable speed circuit which sends very short pulses of electricity (at 50k cycles per second!) to control the motor speed. At $21 it's a low cost improvement that generates negligible heat. The unit I'm considering is available at: http://www.electronickits.com/kit/complete/motor/CKMX033.htm

The only issue is that the heater fan motor ground must come from the PWM circuit and not chassis ground, as the ground is part of the pulse circuit.

Has anyone had their heater motor out to see if there is a separate ground wire for the motor (none of the chassis schematics I've seen show the heater at all.. I guess it was considered an option)?

ratlee2

There is a second wire that grounds to the inside of the case. I ran into the same item with the hot switch and disconnected it as well. I finally hooked it back up a few weeks ago when it stated getting cold here.

RonS

OK. Since I have retired, I have time to track down some gremlins. I took the switch apart and cleaned the contacts. Then I noticed that the wire to the hot terminal was #12 or 14, but the wire to the motor was way thinner, so I removed the motor and added a equal gauge. Surprise! No fuse, so that was added inline.Now, for the first time since Eisenhower, both speeds operate, the switch does'nt get hot and fast speed really turns that way. Thanks for the tips.

schillaz

quote "for the first time since Eisenhower"

HHAHA.........good one!

DocHornet

I took RonS's advice, removed my switch, disassembled it, and cleaned up the contacts (none of which looked all that horrible). Put everything back together, but no real improvement.

One interesting thing is that the switch overheats when in HI position, at which point the wire resistor doesn't come into play at all, should be a direct connection. Hmmm.. I haven't experimented with the low speed yet, but will try it tomorrow.

I may just give up and get a heavy duty bypass switch, and hide it under the dash to turn the heater fan on Hi. Hate to do these kludgy things, but then I don't like having my feet cold either!

Unknown

As far as a fuse for the blower motor, I believe some of the early stepdowns had one on the switch itself, could be wrong on that. The later cars and possibly all of them had it in line on the wire going into the heater box, left side near the gas pedal but up against the heater box.

RonS

Doc,heat in the high position doesn't seem right. I believe that there is too much resistance some where down the line to the fan motor. Disconect the two wires and and jump them across each other( bypassing the switch). May get a bit warm not hot. Is the fan spinning at a good clip? Is it faster then when the wires were plugged in ? What gauge are the wires from the accessory switch and to the fan? I don't know what the correct resistance should be, maybe some one would know that. The fan could be holding back causing a resistance and therby heating the wires. If there was a fuse in line, it probably would blow. It's not too difficult to remove the "weather control box" and bench test the motor.

RonS

Doc, I just went back to your comment on 12volts.That might be it. The fan motor is 6volt. I would think the motor will burn out without a voltage drop placed in line.Ohms Law enters here,resistance(heat)will develop.Ohms=volts/amps.Change volts and amps... you see?

DocHornet

Ken,

I like your approach. Can you suggest a source for the 12V fan motor you installed?
Phil, Austin

RonS

Phil, are you addressing me? I still have a 6v fan in my 53 with the original 6v system. I meant, that, if you have a 12v battery(system),then the fan motor must be changed to 12v, LOL. However you can put a voltage reducer(drop) in the line to drop from 12 to 6v. Fifth ave auto parts in Kansas sells 'em.They operate like a voltage drop in 12 v ignitions.

mars55

For those wanting a 12 volt blower motor, here is Four Seasons dimension chart.

http://www.pageturnpro.com/Four-Seasons/20811-2011-Illustrated-Guide/index.html#/16

[Deleted User]

Hi Ken do you have any part number for the 12v motor you bought from 4 Seasons do you remember the price ?
Jan Sweden