How to install blower motor relays??

[rednesss]

I was getting a feedback loop through the "High" dark green wire that wasn't allowing the relay to turn off so I think a 20A diode there will fix it, since if I pull the dark green wire off of the resistor pack, everything works great.

 

[g413]

You guys did a good analysis of the existing wiring. Another important point that you mention is that on high speed, the vacuum switch also has full current flowing through it, so it needs to be protected too with a relay.

I went out and tried my fan and it works fine on all three speeds, but maybe this is a "heads up" warning.

 

[rednesss]

I'm having a hard time coming up with a way to keep the existing 2 way wiring, one that goes through the A/C-Max A/C and the one that goes through the Heat/Def. Where I currently have my relay, just downstream of the L-M-H switch but before the 3 prong connector won't work when I put it on Heat/Def because the current is routed an entirely different way so that even on high, it goes through 1 of the resistor coils. The only way I can see it working is by splicing the heater switch wire into the A/C wire and just having a single L-M-H speeds instead of a Heat L-M-H and an A/C L-M-H. That is without using like 14 relays and having a convoluted mess of spaghetti.

 

[67Dart273]

Again, I don't have the hardware to mess with this. You might need to get "creative." Maybe use steering diodes in combo with the resistor / switch to shut off one relay to energize the other.

Tell you what, can you give me a functional truth table for that switch? That is, what contacts make when?

 

[convx4]

Sorry to dig up an old thread. Just thought I add some info.
Just doing research in to updating my 65 coronet and 66 valiant blower motor with a relay. On another site it recommended using a single five pin relay right before the motor. This allows the switch and resistor like normal until HI speed is engaged then the relay supply's direct power to the motor. Blower motor wiring diagrams

The 1962 Master tech service book session 174 Air- Conditioned car comfort. Has a diagram that shows a relay for the compressor clutch.
https://www.web.imperialclub.info/Repair/Lit/Master/174/index.htm

I am gonna hope to get this added to my mopar to keep them working care free for years to come.

 

[Hopper]

Thanks again for the help. The relays are installed and working. WOW was I over thinking that project!!

Wondering if you could share some pics of your final solution with relays. Much needed help. Thanks

 

[green72]

Wondering if you could share some pics of your final solution with relays. Much needed help. Thanks

The car is in storage, and I would have to take the dash apart to get pics. I did this quite a while ago, so I don't remember the details. I do know that the info in this thread was enough for me to figure it out. Read all of it. I hope that will help. I would be happy to help if I can.

 

[72RoadRunnerGTX]

Old thread revived it appears. If wanting to relieve the blower motor current draw from the multi-selector switch and retain the original blower speed control function as designed, two relays are required and have to be placed between the muti-selector switch and the resistor pack on the separate brown and tan fan speed selector feed wires. Relays placed between speed selector switch and the resistor pack will interfere with the blower speed control as designed.

 

[Hopper]

Old thread revived it appears. If wanting to relieve the blower motor current draw from the multi-selector switch and retain the original blower speed control function as designed, two relays are required and have to be placed between the muti-selector switch and the resistor pack on the separate brown and tan fan speed selector feed wires. Relays placed between speed selector switch and the resistor pack will interfere with the blower speed control as designed.
View attachment 1716495285

 

[Hopper]

View attachment 1716495515

72 RR - Thank-you very much for the effort on this post!!!!! I followed your directions was able to get the blower motor to work on low, medium, and high when vacuum control switch is on the A/C mode but when you switch to heat and defrost mode on vacuum control the fan does not operate. I noticed the relays shut off when when you switch to heat and def mode. I might be messing something so do you have any suggestions? It also looks like my heater switch just has light green, dark green and tan - no black wire. In your pic you have a black wire to switch not sure if that makes a difference

 

[72RoadRunnerGTX]

72 RR - Thank-you very much for the effort on this post!!!!! I followed your directions was able to get the blower motor to work on low, medium, and high when vacuum control switch is on the A/C mode but when you switch to heat and defrost mode on vacuum control the fan does not operate. I noticed the relays shut off when when you switch to heat and def mode. I might be messing something so do you have any suggestions? It also looks like my heater switch just has light green, dark green and tan - no black wire. In your pic you have a black wire to switch not sure if that makes a difference

Verify you have power coming out of the muti-selector switch on the tan wire (C7A-14T) while in the heat positions. The power to the to the blower selector/resistor pack will switch between the brown (C4A-14BR) and tan wires. A/C positions should have power on the brown wire, no power on the tan wire.

 

[Hopper]

Verify you have power coming out of the muti-selector switch on the tan wire (C7A-14T) while in the heat positions. The power to the to the blower selector/resistor pack will switch between the brown (C4A-14BR) and tan wires. A/C positions should have power on the brown wire, no power on the tan wire.

ok - i will do that and get back to the post.

 

[Hopper]

Also both relays come on at the same time if that matters

 

[Hopper]

Also both relays come on at the same time if that matters

 

[72RoadRunnerGTX]

Adding two more relays as diagramed will remove all of the blower motor current from the blower speed selector switch as well and retain the designed blower speed control.

 

[slantsixdan]

Sorry, yes melt another switch. I was under the impression that this was very common for this to happen.

It isn't. A-body Mopars are decades past their intended lifespan; when you drive an old car, you will find yourself replacing parts most people never have to think about. Blower switches are on that list. If you're melting them repeatedly, your blower motor/circuit is drawing excessive current. Tight/lubeless bearings in the motor are at the top of the suspect list, followed by shorted coils on the blower motor resistor. Fix the problem(s), don't just put a band-aid on the symptom.

That said, yes, it is a very fine idea to put heavy electric loads on relays. Headlamps, blower, and A/C compressor clutch, for example. In the case of the blower switch, you need one relay per blower speed, and as @rednesss mentions, that's +1 on at least some of the A/C cars; '65-'66 A-body factory A/C setups had a resistor-bypass switch mounted near the fresh/recirc door actuator such that selecting "MAX" (recirc) would cut the resistor out of the blower circuit. I don't recall how late such a setup was used, nor what arrangement replaced it.