The blower does not work | Subaru Outback Forums

I found an explanation of the transistorized fan motor control:

With automatic and semi-automatic air conditioning
Control systems, fan motor circuit
the signal is routed through a power transistor
which limits the circuit at all but high speed.
The signal from the control panel is sent to
Automatic climate control module. The signal
an output signal is processed and sent
power transistor. Base voltage i
The power transistor changes due to the signal
from the Control Module, thus changing
fan speed.

[Source: Technician Reference Booklet Technical Training MSA5P0137C Heating, Ventilation and Air Conditioning (HVAC) Module 603, October 2009, page 13]

I am measuring pin 1 on the male connector when it is NOT connected to the fan (How would I check the voltage at the plug when it is also connected to the motor?)

It’s called a backlink search. With the harness connector attached to the blower motor, the tip of the meter’s test probe is pushed into the back of the connector where the wire enters. If the tip is small enough, it may come into contact with the metal pin of the connector. Alternatively, a small wire (like an open paper clip or a pin) can be pushed into the same spot and the meter probe attached/touched to it. In either case, it provides a way to measure the voltage on the pin when everything is connected. Try a Google search for ‘back probe connector’; has photos/diagrams, articles and video links.

Since it seems that the transistor control is not digital/pwm, there should be some measurements that would confirm if it works or not. According to the FSM, when the fan speed control is on, there should be 0.45V on pin 4 of connector B86 (the connector on the resistor/transistor controller). Also, there should be 9V on pin 2 of the same connector. Another thing to check is that pin 1 of the B86 has a really good ground. (The voltages quoted on the FSM are probably with the connectors attached, so backtracking will be used to verify them.) You may find that the voltage at pin 4 varies with the fan speed control setting.

If you can check the B87 two-pin connector on the blower motor again, that would be the first place to check as described in post #5.

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