This is for the two piece unit with the hi fan relay in a seperate module.
Symptoms:
Fan on when ignition is on, the fan switched to max speed when
the control **** is turned to high.
Remove the module from the blower housing, disconnect the air hose and the wiring connector.
The cover on the module is stuck on with self adhesive foam, pry it off the plastic frame.
Notice how much dirt is in the cooling fins of the heatsink. The circuit board is also probably covered with dirt.
Use an air gun to blow out the cooling fins. a small strip of plastic cut from an old credit card works for pushing out some of the dirt as well.
Wash the circuit board off with detergent and water, an old tooth brush help to get in between the parts. Careful not to bend or break any leads.
A few Q-tips or similar are handy to clean off the board between the components so you can read the legends on the board.
Dry thourougly, as the wet dirt is what probably did it in in the first place.
All the transistors and diodes on the board have special oem part numbers. There are no cross references for them.
This board is a simple power amplifier which takes a variable voltage from the control head at H1 and puts it thru a circuit made up of R8,R2, R1, R9
and applies it to the base of Q1. Diode Z1 limits the input voltage to Q1.
The collector (C) of Q1 feeds the base (B) of Q2, which feeds Q3 which feeds Q4 which controls the return current flow from the fan motor back to batttery.
The input voltage to the base (B) of Q1 varied from 8v at low fan setting to 3.5 volts at high. when the control was moved to Max fan the voltage dropped to 1.6 volts.
This indicated the head unit was ok.
I found two problems on the board, There was only a fraction of a volt between the base of Q2 and ground, and there was a cold solder joint on the positive
end of the diode D3. I replaced Q2 with a NPN transistor from Radio Shack, part number 276-2016 and resolderd the diode.
Blower controller now works, depriving the dealer of $375 Canadian loonie's for a poorly designed part.
Bob
Symptoms:
Fan on when ignition is on, the fan switched to max speed when
the control **** is turned to high.
Remove the module from the blower housing, disconnect the air hose and the wiring connector.
The cover on the module is stuck on with self adhesive foam, pry it off the plastic frame.
Notice how much dirt is in the cooling fins of the heatsink. The circuit board is also probably covered with dirt.
Use an air gun to blow out the cooling fins. a small strip of plastic cut from an old credit card works for pushing out some of the dirt as well.
Wash the circuit board off with detergent and water, an old tooth brush help to get in between the parts. Careful not to bend or break any leads.
A few Q-tips or similar are handy to clean off the board between the components so you can read the legends on the board.
Dry thourougly, as the wet dirt is what probably did it in in the first place.
All the transistors and diodes on the board have special oem part numbers. There are no cross references for them.
This board is a simple power amplifier which takes a variable voltage from the control head at H1 and puts it thru a circuit made up of R8,R2, R1, R9
and applies it to the base of Q1. Diode Z1 limits the input voltage to Q1.
The collector (C) of Q1 feeds the base (B) of Q2, which feeds Q3 which feeds Q4 which controls the return current flow from the fan motor back to batttery.
The input voltage to the base (B) of Q1 varied from 8v at low fan setting to 3.5 volts at high. when the control was moved to Max fan the voltage dropped to 1.6 volts.
This indicated the head unit was ok.
I found two problems on the board, There was only a fraction of a volt between the base of Q2 and ground, and there was a cold solder joint on the positive
end of the diode D3. I replaced Q2 with a NPN transistor from Radio Shack, part number 276-2016 and resolderd the diode.
Blower controller now works, depriving the dealer of $375 Canadian loonie's for a poorly designed part.
Bob
