No it wasn’t set to auto, and Yes the fan was on max the majority of the time. I was thinking similar regarding the relay being removed
This is getting complicated. I wouldn't discount the fan or fan controller as being faulty, especially if you were not in AUTO (fan). Manual fan control allows the driver to decide what the fan does. There is no mention of the fan stopping in the workshop manual. The fan/controller may be drawing some high currents, enough to overheat something and stop the fan running, but the circuit breaker may simply not be popping because you are not running the compressor at the same time.
What you need is an amperage meter. Put everything back together. Turn on the A/C compressor. Check the amperage at the clutch circuit. Turn it off. Turn on the Fan , check the amperage. Compare the readings to the factory rated amperage for these devices. If nothing is out of the ordinary put the meter on the wire to the fuse. Check the amperage. If it's getting close to the rated fuse amperage you have a item in that circuit that is starting to fail and is drawing high amperage. If the fuse just "pop" with no high amperage you have a short some where.
I bought myself a Fluke "amp clamp" meter, which allows you check the current with the wires still connected (amperage measurement traditionally requires you to put a meter in series with the wires). https://www.ebay.com.au/itm/264259902181? These are generally more expensive than your average meter, but desperate times need desperate measures. The model above does have limitations on resistance measurement however (4Mohms if I remember correctly).
That one should do nicely. Another trick is to wind the wire around the clamp multiple times to increase the reading to get a more readable number. Ie wrap 5 times get say 3.5 amps. Divided by 5 , actual amps .7. This test Should point you in the right direction now.
Some basic info: Compressor - The only part of the compressor that could cause fuse tripping is a fault in the compressor clutch solenoid (coil), easily replaced and available as spare. The clutch solenoid coil normally draws about 3.5 - 4 Amp so it is not really a major load on the AC Fuse, unless it develops internal short which can also be intermittent or when the coil heats up. Isolating the compressor clutch solenoid will tell whether the problem is there. There is no harm keeping it off for any period of time. Blower Fan - This is the main consumer on the AC Fuse, probably 10 Amp or more. If there is any overload there, it can only be caused by the fan motor, not by the fan speed controller. Partial seizing of the motor, or partial shorts in its windings, will cause high current draw which can blow/trip the fuse. Another question is: Is the tripping fuse good? Perhaps it developed a fault which causes it to trip earlier than the stated 30A.
Thanks Miro. I assumed that because the fan current flows through the controller (to earth), that a short in the controller could draw excess current. Would the normal resistance of the fan motor coils stop this?
The controller's circuitry is connected in series with the fan motor. The +12V supply goes to the motor "+" and the motor "-" goes to the controller which "shorts" it to the ground, more or less, thus controlling the fan speed. If there is a short in the controller, it would only cause the fan to run at full speed and nothing else. The controller actually deliberately shorts itself to the ground when you select the "max" fan speed. At "max" selected, the controller activates its internal relay which literally shorts (bypasses) the electronic speed controlling circuit (the two power transistors) so the full motor current runs through the closed relay contacts to the ground and not through the transistors.
Thanks, Miro. So this may reduce the number of possibilities. Faulty fan motor (as the fan is momentarily cutting out) even with the clutch relay removed. No fuse trip perhaps because only the fan motor is being powered? Multiple problems (fan and clutch). According to the WSM, the regulator sends a temperature signal to the HVAC ECU and the ECU controls the regulator accordingly. Is this an incoming air temperature signal or is the temperature related to the power circuits in the regulator? Can the ECU command a "fan off" signal if temperatures get too high? I'm trying to understand why the fan is stopping for a few seconds. If the ECU or regulator senses a fault and the default max fan speed is commanded, is there a few second switching time?
The signal going from the Fan Controller (from the middle pin of its small connector) back to the AC ECU provides information on the temperature of the power transistors of the controller, not any ambient. I presume that, if the transistors start overheating, the ECU will interrupt the current flow through the controller for a while and re-connect when the transistors cool down a bit. The transistors will overheat if the blower motor draws excessive current so this suggests some fault in the motor - either partially seized (dry) motor bearings or a fault (shorts) in the motor windings.
Ouch. Our condolences. I think that's an entire evaporator change. I can't say I've heard of anyone being able to open up the evaporator (at least not in-situ)
