Adding a relay to the Heater Blower switch

[Steve Graham]

I'm putting in my 4th heater blower switch and they all have failed the same way. The contacts for the high position have burned up. The contacts cannot handle the current for long duration in the high positation with AC.

I remember several years ago some of the TDR members added a relay for the high position and I'd like to know how. I've got the insterment cluster bezel off and putting a relay behind there would be a nightmare.

Any ideas?



Steve

 

[Niki]

You'd probably have to find the resistors that control the fan speed and wire a relay into the resistor for the high position.

 

[Steve Graham]

Yes I've got the glove box out and found the resistor board. Just got back from Kinko's with 10 copies of the schematic, page 73. Traced out the power through the high position. Looks like all positions on the blower SW are hot, the input just directs the current. If I use the high position to signal the relay, it will come on, on any position. This is going to be fun.

 

[dpuckett]

Let me know how it turns out. I put a relay on my high position off the switch, and I now have to turn on the VENT, then put it on HIGH, and move to HEAT, DEFROST, or whereever. Works like it should on AC and VENT. If I turn it off with te switch on HIGH, it still blows. :-laf



Daniel

 

[1stgen4evr]

It is at least possible that you are chasing the wrong problem. I have also had trouble with my blower control switch, but in the end, what I had was a blower motor that was drawing too much amperage. I experienced this on my 93 and also on the 97 which has a different system. The motors don't have any way to re-lubricate them and the oilite bushings get to the point that they tighten on the shaft. (Yes tighten, not floppy loose) It would probably cost an extra 38 cents to build one with better bearings. And the bean counters are in charge, not engineering.



And even the Wonderful One Horse Shay gave up after a while.



James

 

[Steve Graham]

Let me know how it turns out. I put a relay on my high position off the switch, and I now have to turn on the VENT, then put it on HIGH, and move to HEAT, DEFROST, or whereever. Works like it should on AC and VENT. If I turn it off with te switch on HIGH, it still blows. :-laf



Daniel

Danial,

The first thing I thoughtwhen I looked at the schematic (FSM) page 73 was that Dodge had the schematic wrong. It shows that the blower SW has a Off, LO, Med, and HI. I say no way mine goes from low 2,3, and HI.

Heres how the SW works, On LO the SW is open, all current goes through the resistors. On 2nd notch up, power goes to the LO pin on the Schematic. On the 3 notch up power goes to the LO and MED contacts. On HI power goes to the MED and HI contacts. Guess they were trying to distribute the power over several contacts.

So what you have to do is put a relay in for the top 3 setting, because if you look at the schematic, all contacts have power to them when the blower is on. You can't just use the HI lead as a signal, because it has power to it all the time. I'll draw it up and post it soon.

 

[Steve Graham]

It is at least possible that you are chasing the wrong problem. I have also had trouble with my blower control switch, but in the end, what I had was a blower motor that was drawing too much amperage. I experienced this on my 93 and also on the 97 which has a different system. The motors don't have any way to re-lubricate them and the oilite bushings get to the point that they tighten on the shaft. (Yes tighten, not floppy loose) It would probably cost an extra 38 cents to build one with better bearings. And the bean counters are in charge, not engineering.



And even the Wonderful One Horse Shay gave up after a while.



James

James you could be right, I'll hang a amp meter on it and find out. If I can find a inexpenceive amp meter.

 

[MeritBadge]

I second the excessive amp draw, that was the issue with my 93. Replaced the blower motor and the amps on HI were nearly half of the old blower motor's amp draw.

 

[dpuckett]

Hadnt considered the amperage draw. That could also explain the slight burnt appearance of the pigtail for the switch. More electrical stuff. Fun, fun, fun. I'll hook up my multimeter and see what's up. It was only getting 7. 5 volts TO THE MOTOR before the relay install, which led me to believe it was either the resistor, or something in bewteen it all.



DP

 

[Steve Graham]

I broke down and put in a new blower motor. A amp guage would have cost more so I figure I'm ahead. The old one defentily had some problems, dry bearings? hard to turn compared to the new one. I checked voltage at the motor, not a problem. Drove it for an hour, AC on full blast, (yes it's summer in Phoenix already) when I got home put my laser thermometer on the connector of the blower SW, read 105 F, the 10 ga. supply wire was at 96 F.

I wonder if I still have a problem? Have not put in the relays.

 

[dpuckett]

Tested the amp load on my motor, and it blew the fuse in my multimeter as it zoomed by 15amps. So, what is the spec for max load draw for the blower motor? Is mine within spec, or is it too high? I couldnt find anything in my manual regarding this.



Daniel