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Topic: manual heater control mod rev4 is this still valid? (Read 1636 times) previous topic - next topic

manual heater control mod rev4 is this still valid?

has anyone but one person we know of used this to modify their heater controls?

this was researched and solved because one of our members here listed on the drawing noticed the blower speed switch was discoloring and looking to be in bad shape.

we designed this mod around the 97 explorer manual heater system which has slave relays for both the speed switch and the blower motor.


I am attaching the before and after shots to help illustrate things.

Re: manual heater control mod rev4 is this still valid?

Reply #1 –
here is a pic of the speed control switch sorta laid out in like an illustrated parts break down as best i could.

root cause for heat .......

either... wiring is too small  yet the wires themselves are not telling me they are over heating...
or................

what i highly suspect is the root cause is the amount of pressure the two springs offer to push the tiny metal sled along the contacts.  so.. i am going to "stretch out" the springs a tad to assure more pressure. 
that is it for now on my son's manual heat control ,,, slave relays can come later.

Re: manual heater control mod rev4 is this still valid?

Reply #2 –
Not sure what you mean by still valid.
The blower will run. But in the M1 and M2 positions, the blower will run slower that stock.
This is because the three speed control resistors have different resistance values.
From the 84 shop manual: From the top down, the resistors are 1.7  .7  And .3 ohms

In the M1 and M2 positions it is bypassing the thermal limiter safety device. If the air flow is blocked the resistors will overheat.
From the 84 shop manual: Current draw in Low 5 amps, M1 8 amps.  M2 14 amps and Hi 22 amps (stock wiring)

Re: manual heater control mod rev4 is this still valid?

Reply #3 –
well i did not know that,,,

back then i had assumed the resistances were equal.  with that in mind, you can prob understand why ii flipped the M1 and M2 positions at the switch.  I did not even know to think about this as a question so again, i assumed they were the same ohms.

so,,, i was asking kind of a two fold question,, first if anyone else did this yet along with lessons learned ,, and to have someone else verify the diagram before i fiddle with wires to do this myself.


again, you tend to bring some good details to most any topic.

Re: manual heater control mod rev4 is this still valid?

Reply #4 –
  • Don't do the pin swap of the M1 and M2 wires at the switch. leave them stock
  • Move the N/C output wire from the lower relay to the bottom of the resistor stack. I don't see any need for the 30A fuse in this circuit.
  • Move the ground wire to the top of the resister stack.

For some reason I can't get the numbered items list thing to go past #2. Finely got it>

Re: manual heater control mod rev4 is this still valid?

Reply #5 –
thats actually what i have now , since i now know the resistors are actually different values.   i'll repost