Relay on blower motor

[gogmorgo]

I was thinking the purpose of this is to reduce load on the ignition switch, in particular the brown wire, yes? So you would stick the relay ahead of the speed selector switch, and use the 12v feed from the ignition to trigger it.

Not using a relay would mean your fan was getting constant power. Just sticking in a bigger wire for the 12v feed wouldn't reduce the ignition switch's load, and power would still be getting bled off by all the other circuits getting power through the ignition. The increased voltage (and subsequent reduced load) to the fan switch when using the relay is only a happy coincidence.

[Rockfrog]

 

 

I was thinking the purpose of this is to reduce load on the ignition switch, in particular the brown wire, yes? So you would stick the relay ahead of the speed selector switch, and use the 12v feed from the ignition to trigger it.

Yes, brown wire becomes the blower switch "signal" wire, and a new feed wire goes through the relay to the switch. Thereby reducing the load seen by the brown wire, and possibly helping the blower circuit with a full voltage feed. Which if all things I've thought are right, should also reduce the Amperage at the switch by way of increased available voltage. Which is usually the root of all evil with the MJ's wiring, massive voltage drops increasing average loads. At least the way I see it.

[Eagle]

That makes sense.

[Gene]

Hi gentlemen,

 

This gets really confusing, but Ohms Law  is actually I=V/R  or   current= voltage divided by resistance 

 

Watts (power) = V x I (volts x amps)

 

So if you keep resistance fixed, decreasing voltage DECREASES current flow.

 

So a load that is 120 watts at 12 volts would only be 100 watts at 10 volts. That's why lights dim, or motors run more slowly.

 

 

The problem is when there is resistance somewhere else in the circuit. Let's say a connection is corroded. There will be resistance at that corroded connection. The voltage drop at that connection actually generates heat. Lets say the current through the circuit is 10 amps. The voltage drop at a corroded connection is 2 volts. So 2 volts x 10 amps= 20 watts of heat will be generated at that connection. That heat will melt plastic, make insulation brittle, and further corrode the connection. More corrosion= more resistance=more heat=more damage. Hence connections fail, wires short, and (worst case) fires occur.

 

So the relay suggested above will primarily make much better connections through the circuit, decrease resistance in the circuit, decrease voltage drop, and minimize overheated connections.

 

Please let me know if any of this does not make sense.

 

Gene

[91Pioneer]

My blower fuse was melted and bypassed with a jumper wire on my new 89 Comanche.

 

Did anyone actually ever get around to installing a proper relay on a Renix blower motor? Perhaps could share experience or a diagram on where to tap the wire into (for sure)....?

 

I intend to pull the dash apart and check the fan speed switch wiring harness to see if it's melted or not too. The wiring at the resistor is perfect and new looking. The blower wiring under the hood looks good.

 

I also plan on adding an extra ground wire for the blower as per cruiser54.

[91Pioneer]

Bump.

[cruiser54]

 

[91Pioneer]

I know how to wire one relay, I'm trying to figure out like do I need to wire 4 relays or 1 relay and where in the circuit does it go? I don't understand because of the different speeds I don't think a single relay would work with reduced voltage on lower speeds??

[cruiser54]

How about a relay to the main power circuit of the blower motor? 

[91Pioneer]

6 minutes ago, cruiser54 said:

How about a relay to the main power circuit of the blower motor? 

My fuse is melted and the power side of the fuse connector is broken off (just the one side that feeds the blower still exists) so I was thinking I need to put a relay between the fuse wire and the blower motor but there are connections there, fan switch, and the resistor thing. I wonder if I can just put it just after the fuse somehow?? I'm not too sure, I was just thinking someone must have done this already so I was trying to to reinvent the wheel so to speak.

[gogmorgo]

There was another thread not too long ago where I dug up the circuit diagram. I think ideally you’d be putting it between the speed selector switch and the resistor pack, but you’d need an individual relay for every fan speed I think. Otherwise I would say the next best place would be just ahead of the hvac controls.

 

[Ωhm]

On 6/4/2023 at 1:04 PM, 91Pioneer said:

My fuse is melted and the power side of the fuse connector is broken off (just the one side that feeds the blower still exists)

 

You'll need to fix/solve this first.

 

 

I think when they bypass the Blower Switch, only the HI circuit is bypassed. Proof the following, should do the job. If you want M2 circuit relayed, do it the same way.

 

[91Pioneer]

I'm still very confused by all that going on LOL but I did solder an extra ground wire from the ground wire coming out of the blower motor (just past the connector) directly to a bolt on the inner fender where I also ground the battery. The ground is direct and pretty short so that must be an improvement.

 

I think I have the fuse area "good enough" for now, as there is a small jumper wire with a 25A fuse in it with spade terminals on the end. It goes from ACC to the blower fuse spot and I have inserted toothpicks to ensure a very tight contact on the terminals. It's so tight I could barely plug in the spade terminal, so at least those connections are very solid now.

[Ωhm]

"X" means cut the wire. Relay is as follows: