Two speed rear heater. (1 Viewer)

[jm599]

Rusty72
My oem resistor gets very hot when on low speed. It looks like it's supposed to.
Ceramic coating?
I had to solder the edge earlier to get it to work due to looseness and corrosion

I think all resistors give off heat?
Nature of the beast?
Like an electric stove?
Cooler man would know.
To get the voltage drop...so it's on low speed?

 

[Rusty 72]

I will assemble it with the 50 watt resistor and see how it works.

 

[73tlcv8]

If you can measure the current to the fan while running in low, you can find the heat (watts) dissipated by the resistor P = I2 x R, then go up to the next higher rated resistor. If you select 50 watt resistor, the current would have to be more than 3.5 amps to overheat the resistor.

 

[jm599]

73tlcv8, you remember your physics
Much more than I do. "I" is current in amps? As in "V=IxR"?


Did a better search, found a Coolerman rec several years ago and ordered this


L50J1R0 - Ohmite - Bracket Mount Resistors | Galco Industrial Electronics

 

[73tlcv8]

73tlcv8, you remember your physics
Much more than I do. "I" is current in amps? As in "V=IxR"?


Did a better search, found a Coolerman rec several years ago and ordered this


L50J1R0 - Ohmite - Bracket Mount Resistors | Galco Industrial Electronics

Good find.

yes, I = amps

 

[Living in the Past]

73tlcv8, you remember your physics
Much more than I do. "I" is current in amps? As in "V=IxR"?


Did a better search, found a Coolerman rec several years ago and ordered this


L50J1R0 - Ohmite - Bracket Mount Resistors | Galco Industrial Electronics

Think you would find at four inches that resistor would not fit very well inside the rear heater. Looks like a good fit for the blower motor under the hood. Thinking of converting the 8/80 and later rear heater to a two speed. Would have to find it but have a FJ62 rear heater that is similar and two speed. That resistor might be a good option.

 

[Rusty 72]

I measured the amps and got 1.1. Ran fan over 1 hour on low and resistor temp was 136. I think this will work.

 

[Living in the Past]

I measured the amps and got 1.1. Ran fan over 1 hour on low and resistor temp was 136. I think this will work.

Few things to consider. Enclosed with the top and coil will changed the amp draw. But if D/C voltage is like A/C voltage amp draw will drop a little. The 136 degree will change when the air coming thru the coil and over the resistor has engine coolant running thru it. I'm sure it will be much higher than 136 degrees.

 

[Rusty 72]

I cleaned the motor up and now it's drawing .75 amp. Has been running for several hours and resistor temp has risen to 194F. I looked on Mouser for the specs. It's max operating temp is +200C. It should stay well below that temp after it's mounted on the metal heater frame.

 

[stoshzack]

For anyone interested, I replaced my resistor with this:

CLAROSTAT VP10FA RESISTOR 5 OHMS ADJUSTABLE WIREWOUND RESISTOR, 411 9132, NIB​

You can find it on eBay right now. The resistor allows for variable resistance, but I just used it without the variable bracket. It measured 4.8 ohms without variable bracket. My previous oem resistor measured 4.4 ohms. It is a little bit longer than own, but shortening the bracket does the trick.

Comparison pic and installed pic