Current going to Blower Motor can be higher than Headlights - why no relay mod?

[Gary Lewis]

Gary,

I think the colors and splices were pretty clear in my pics. (At least, I tried)

At first I had it wired with some backfeeding, and the relay (and motor) would stutter.

I assume when the relay closed the ground side of the coil went high and the relay would drop out.

It would be interesting to see Ford's instructions.

There must be a TSB for the vans effected.

Jim - The colors are clear in your posts, starting here. And I'm going to do that mod. I just ordered the kit from Utech. However I'll pick up power to the relay & blower from a fuse in the PDB.

Unfortunately I didn't measure the voltage drop to ground before installing the ground relay. But I already know the drop to the motor on the high side is 2.0 volts at 12.8 battery voltage. My understanding is that dc motors have linear current draw with respect to voltage, so at 14.4 volts I'm guessing the voltage drop will be 2.3 volts. The relay should cut that to essentially nothing - at all speeds. And it'll take that much load off the cab circuits.

[Gary Lewis]

Jim - The colors are clear in your posts, starting here. And I'm going to do that mod. I just ordered the kit from Utech. However I'll pick up power to the relay & blower from a fuse in the PDB.

Unfortunately I didn't measure the voltage drop to ground before installing the ground relay. But I already know the drop to the motor on the high side is 2.0 volts at 12.8 battery voltage. My understanding is that dc motors have linear current draw with respect to voltage, so at 14.4 volts I'm guessing the voltage drop will be 2.3 volts. The relay should cut that to essentially nothing - at all speeds. And it'll take that much load off the cab circuits.

Jim - I just perused the TSB index (Documentation/TSB's/TSB Index) and didn't see anything with regard to a blower motor relay. Do you know when that kit was issued? Does it have a part or ID#?

[ArdWrknTrk]

Jim - I just perused the TSB index (Documentation/TSB's/TSB Index) and didn't see anything with regard to a blower motor relay. Do you know when that kit was issued? Does it have a part or ID#?

Same as your eBay picture....

But it does have a Ford tag on the socket/harness.

Ill take a look later.

[kramttocs]

Jim - I just perused the TSB index (Documentation/TSB's/TSB Index) and didn't see anything with regard to a blower motor relay. Do you know when that kit was issued? Does it have a part or ID#?

Gary - does yours not completely negate the resistor though?

A 5 pin relay is the only way I can think to do this allowing the non-high speeds to be on the NC contact.

Edit: I just reread the early posts in this thread and see that Bill outlined that in the post where the diode was mentioned.

Edit 2: Diagram-

 

[ArdWrknTrk]

Gary - does yours not completely negate the resistor though?

A 5 pin relay is the only way I can think to do this allowing the non-high speeds to be on the NC contact.

Edit: I just reread the early posts in this thread and see that Bill outlined that in the post where the diode was mentioned.

Edit 2: Diagram-

I don't see a diode..... ----[>|---

Maybe that's what was causing my troubles at first.

[kramttocs]

I don't see a diode..... ----[>|---

Maybe that's what was causing my troubles at first.

Yeah, I am still unsure on if the diode is needed and where it would go so it's not in there . In just the high switch wire? Both switch wires? Motor side ground wire?

[Gary Lewis]

Gary - does yours not completely negate the resistor though?

A 5 pin relay is the only way I can think to do this allowing the non-high speeds to be on the NC contact.

Edit: I just reread the early posts in this thread and see that Bill outlined that in the post where the diode was mentioned.

Edit 2: Diagram-

I don't have a diode in the blower motor circuit. I used the diode that is in the PDB on the starter circuit.

Yes, my existing relay negates the resistor, but it only comes in when you switch to High.

My thinking on the power side is to put it on the left side of your drawing, and that is probably what you mean by a "hot" relay. It would provide all the power to the motor, regardless of speed setting. That will probably increase the speed in all settings by some percentage, and I'd expect that to get essentially all of the 16% in High. But as the resistors come in and the current decreases there'd be less voltage drop with the factory approach so less and less increase in speed as you go down on the switch settings.

[Rusty_S85]

Interesting idea to splice a relay in for the blower motor. I know I will be splicing a relay in on my A/C clutch circuit how ever for my fuel injection to have A/C cutout when I go full throttle. But for the blower itself I never thought of going with a relay for both blower motors.

Never had a connector burn up on mine, the heater blower under the hood I do need to replace the terminal but thats only cause the locking clip broke and I have a zip tie holding it plugged in currently. Real pain when I take the blower motor out to oil the shaft as my blower tends to rust up. Been thinking about trying to source a NOS blower motor just cause of that.

[ArdWrknTrk]

Yeah, I am still unsure on if the diode is needed and where it would go so it's not in there . In just the high switch wire? Both switch wires? Motor side ground wire?

If you look at my pictures you'll see that -at first- I had put the relay in the O/BK wire.

Using it to take the motor to ground with the relay closed -and- letting current flow through the resistor block with the relay open.

But I needed a rethink on that, so went and disassembled the upstream splice, put a butt connector where I had tapped it originally.

[Gary Lewis]

If you look at my pictures you'll see that -at first- I had put the relay in the O/BK wire.

Using it to take the motor to ground with the relay closed -and- letting current flow through the resistor block with the relay open.

But I needed a rethink on that, so went and disassembled the upstream splice, put a butt connector where I had tapped it originally.

My guess is that the high-side relay is probably twice as effective as the low-side relay. The high-side has pretty large wiring going into the cab from the starter relay to the ignition switch, then still large wire to the fuse box, and then smaller wire to the function switch and then to the motor. So while it goes twice as far as the low-side wiring it has lots of connections in it, and surely the connections have voltage drops in them.

Having measured the high-side voltage drop it now seems like I should measure the low-side drop. And I think I can do that by pulling the relay and jumpering 86 to 87. That will use the factory wiring, and I can measure from the motor's connector to the negative terminal of the battery for the voltage drop.

Headed to the shop......