How to install blower motor relays??

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green72

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72 Scamp /6 A/C. I would like to install relays for the blower motor switch so I won't melt another one! I have been staring at the wiring diagram this afternoon and am not seeing how to do this. If someone has done this and could get me going in the right direction I would be grateful. Will I need a relay for each speed?

Thanks
 
Melt another one what, the switch? Maybe the blower is drawing too much current or the switch connections are loose. I would not bother with relays.

"I guess" you'd need three relays. These are three speed, right?
 
Sorry, yes melt another switch. I was under the impression that this was very common for this to happen.
 
The wire blower HI through a relay might extend the life of the switch. Lower speeds run through resistors. Relays shouldn't be needed on those.
 
2 in a short period is a sign of another problem. Clogged heater core would be my first guess.
 
If you really want to do relays, then you will need one for each speed.
The resisted speeds still draw the same amps at the switch it's just that the resistor uses some of the amp so the motor runs slower.

This means that each wire off the back of the switch would need it own relay, and then the resistors would still function as they do now.
But the switch would be under way less of a load (like you are asking about)

I drew a diagram for someone on here just awhile back, so let me see if I can find it.


Here it is.
This was for a two speed blower, so if you have a 3 speed just add another relay for the third speed wired the exact same way.
 

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This is the diagram for my car. I am unclear how to run the power to the relays. The fan comes on low when you push either the A/C or heat buttons. The ignition on power comes to the back of the A/C heat control and splits in to two leads. I believe that one runs the low speed and one runs the med and high is this correct??
 
Thanks for the diagram Trailbeast. You drew that for me a couple weeks ago. For some reason I am not seeing how to do this (could be lack of skill??). I would really like to take the load off the switch. they are hard to find and hard to replace. Try to explain it so a 3rd grader can understand LOL.
 
Ok lets try this.
You can do this right at the blower so all that confusing wiring in the diagram does not matter.

The wire at the blower for the low speed position would get cut in two.
The switch end of that wire would connect pole 86 on the relay.
The heater end would get connected to pole 87 on the relay.

For the second blower speed, it's wire would get cut in two and the switch end gets connected to the same poles on the next relay and then continues on to the heater via the second speed wire.

The relays just act as a electrically operated switch that can handle a lot more amps that your dash switch.
All the dash switch would be doing after this is activating the relay for each speed, so the first relay would be for low, and the second relay would be for the second or high speed.

If it's a 3 speed blower, you just add another relay for that speed wired exacly the same as the others. (but using the 3rd speed wire.)

The wires (positive and negative) at the bottom of the diagram are what would now supply the blower with power and your dash switch would just be a light duty switch to activate the relays.

Keep in mind that a relay is only a electrically activated switch, that's all.
Terminals 85 and 86 make it switch on and off, and terminal 30 is where power comes in instead of going through your dash switch.
Terminal 87 on each relay is your blowers new power supply for each speed instead.

Ask if you need to.
 
Trailbeast has been great helping me with this but more info is always good. I decided to install the relays in the wires just behind the switch. I am confident that I am wiring the relays correctly. My car has a 3 speed fan, low comes on when the A/C or heat button is depressed med and high are controlled by the fan switch. I am seeing a low voltage at the med and high wires at the switch when it is in low position. Where is this coming from? Is it coming thru the resistors?
 
Trailbeast has been great helping me with this but more info is always good. I decided to install the relays in the wires just behind the switch. I am confident that I am wiring the relays correctly. My car has a 3 speed fan, low comes on when the A/C or heat button is depressed med and high are controlled by the fan switch. I am seeing a low voltage at the med and high wires at the switch when it is in low position. Where is this coming from? Is it coming thru the resistors?

Ok, I see what you mean now.
That shouldn't matter because with the relays in the line that low power would feed back to the 87 terminal of the relay and stop there due to the relay not being active.
 
I don't know if this will help or not.
It might show you where to connect the relays.
The first part is a bit boring.
[ame="http://www.youtube.com/watch?v=mHmYJWVb25I"]How to Wire 4 Speed AC Blower Relay - YouTube[/ame]

You may need only the 2 relays one for the high and medium because they don't have all the resistors like the low does, but it probably wouldn't hurt.

I did these diagrams . I think this is how it works. I'm not a wiring expert. If someone wants to correct them go right ahead. It would help the rest of us too.

View attachment low.jpg low

View attachment med.jpgmedium

View attachment high.jpg high
 
I am confident that I am wiring the relays correctly. My car has a 3 speed fan, low comes on when the A/C or heat button is depressed med and high are controlled by the fan switch. I am seeing a low voltage at the med and high wires at the switch when it is in low position. Where is this coming from? Is it coming thru the resistors?

Post a diagram, even a photo of hand drawn, of how you wired these

Yes, there will be feedback on the unused speeds when not selected. If you wired it correctly, the unused speeds will be "opens" at relay contacts and won't go anywhere

Without seeing how you hooked this up, we are only guessing.
 
Thanks guys for the help!!! Ok the feedback is normal that is good to know. I will post a pic as soon a I can. The feedback also comes thru the relay, Could I have the wrong relay it should be open until that switch position is selected and no feedback getting thru right?
 
. The relays are installed and working. !

Ya know there are a couple of reasons I asked you to post a diagram of what you did

1.......to help others. If you have truly discovered a good, easy way to wire these, that would be something to pass on

2......It would be a shame that if you got this all hooked up you were to find out that you actually still have the switch acting as the main supply line. After reading some of this discussion, I'm not so sure.
 
If he wired them like the diagram I posted above, then all should be good.
 
Can anyone put a diagram, using the wiring diagram from the repair manual a few posts up, and show exactly where to put the relays at? I tried putting a relay using the dk green output from the switch as the trigger wire for the relay and the load output from the relay I butt connectored to the other side of the dk green wire running out to the blower motor. It works, but somehow I am back feeding the relay so that it doesn't shut off when I cut the power or turn the key off. Somehow I'm getting some circular power. I need some help.
 
I should add that as soon as I move the switch to medium or low and then turn the key off or put the controls on off it stops working. I thought about trying to figure out where it's backfeeding and put in a diode.
 
You need to post the car year and model for starters. The whole key is probably the switch and resistor. My car is "all the way apart" for now, and I don't have the means or time to jig this up for testing
 
I guess I'll see what I can figure out on my own. I will do what most people don't, and actually post back as to the solution, not just say I fixed it without explaining how.
 
It is mainly the "blower high" position that melts the switches, so I put a relay for that position alone in my 69 Dart and 65 Newport. That was after melting both the pneumo-electric push-button switch and the L-M-H switch. Below are sketches I made of the wiring. Can't give details since this was c.a. 1993, but same as above, use the "blower high" wire to turn on the relay coil (86, 85 to gnd) and wire the relay output (87) to where the "blower high" wire was going. Supply the relay w/ 12 V from ACC circuit (to 30, sideways pin).

I include the pneumatic plumbing since was fooling with the push-button, and also had to figure how to use a 5-button to replace my Newport's 4-button (unobtanium). The Dart was a factory AC car.

BTW, this is hardly a Mopar thing. 1980's M-B cars like to melt the #8 fuse-holder (blower). Indeed, just today I was wiring a relay to power the "blower relay box" in my 1984 300D (like I did in my 1985) before its fuse-holder melts (like my 1985 did).

A funnier blower story. My dad checked the blower fuse in our 70's Matador wagon and "looked good" (no frebbie HF multimeters then) so he put it back and we suffered thru 5 summers in FL w/o AC because "too expensive to fix". He finally found the fuse was open and melted right at the tip where not visible, not from over-current but rather heat from the corroded terminal in the fuse-box (this was FL). Changed the fuse and we had AC again. Actually, he put in a breaker-type fuse that resets automatically.

Moral is you have to redesign this stuff in many cars. The manufacturers are striving for a price point, and just have to meet the warranty time. The new electronic blower controls are better, but even the one in my 2002 T&C failed (common problem) and a replacement "resistor pack" (actually transistors) cost $60, but it was a better redesign.
 

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I think I have it figured out, I'll put up some detailed diagrams of what I end up doing. To do it right, you need 4 relays, 3 for A/C mode, and 1 for heat/def mode. As it seems that when on heat/def mode, even high speed runs through 1 of the resistor coils via the 14BR wire instead of bypassing all of them in A/C mode via the 14T wire. In heat/def mode, there really is no way to not have the current run through the L-M-H switch.

High - Heat/Def mode
 
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