The blower power transistor module consist of several components: transistor, thermal cutoff, resistors, and capacitor.

You can test the thermo cutoff and the other parts.

This link has more information regarding the transistor and the thermo cutoff.

The thermo cutoff is inexpensive and easy to get via sites like Digi-key; I bought some before. Pick the cheapest shipping method if you order.

How to fix AC (Blower) transistor module - HondaSUV Forums - Discussion forum and bulletin board for Honda CR-V, CRV, Element, Pilot, HR-V owners

 

Yes, low speed settings require the transistor (variable resistance) to reduce current flow w/ resultant heating.

Thermal fuse is tested for continuity (near zero resistance) is good, and open (infinite resistance) is failed. I tested w/ component mounted to find open fuse. In my case, a MDX transistor, the air inlet to the transistor was blocked so reason for failure was obvious.

Only way to know if blower motor is source of problem (if new unit is indeed failed also) is to perform a current demand test w/ VOM rigged in series to measure current flow. Blower motor is fused for 40A, so need probably at least 20A current measurement capacity.

See following link for pics and sources for thermal fuse if you decide to DIY.

Rear blower Transistor Fix - Honda Pilot - Honda Pilot Forums

I can't say whether leaving the transistor out of heater box could have contributed to failure, but certainly there would be reduced heat dissapation in that configuration.

good luck

 

I'd guess that if they went to the trouble to mount that in the fan housing, that means it needs the air flow for cooling.

 

You know, you may have a point there.


Checked the thermocutoff on both the original and new transistor, and they both had no continuity. So I guess that's my problem - overheating. How do I check to make sure the air inlet isn't blocked?


Also, I'm going to replace the cabin air filter too.

 

If air is exiting the vents, then air is blowing over the transistor. Only possible sources of blockage are 1) cabin air filter and AC evaporator core. Heater core is bypassed for all cooling-only conditions.

good luck

 

Blockages from debris inside the fan housing??? You occasionally hear stories about mice making a nest in there. I suppose that would cause more problems than just an overheated controller.

 

OK. So I got a soldering kit, a new TCO and went to work. I've never soldered before. I used a desoldering wick, which worked well on the TCO, but it was a bit tricky on the MOFSET because of the 4 prongs, but I got it unsoldered.


The only TCO they had in stock locally was a 117C 10A 250V, which the friendly old guy said would work just fine (not sure if I believe him). Other than it not really fitting because it was larger, I jammed it in with plenty of thermal paste. Resoldered the connections. Not knowing how to do it, I tried a TIG welding technique which didn't work too well, but I think I have solder everywhere...


So I put it in, cranked on to start, and....


The blower now runs on high, regardless of the setting- even off. I still have 1500OHM resistance on 3-4 and 0 on the new TCO... What's next in the saga? If I messed this one up, I have the second transistor I bought which lasted 5 minutes. Quick Update: Checked the resistance on the 1 and 2 terminals on the transistor I soldered and it's 11Kohm vs the untampered one that seems to be extremely high.


Any advice?

 

For the blower motor to run w/ blower Off and ignition off, the blower motor relay must be shorted or stuck closed. Power transistor likely has failed to short circuit or less likely, the power transistor bias line (blu/yel) is commanding short circuit condition of power transistor. This should not be possible w/ ignition switch OFF.

Suggest pulling blower motor relay w/ ignition switch OFF and see if blower goes off.

If yes, then w/ ignition switch off, check power transistor resistance on lines 1-2 (wht/blu to blu/blk). If shorted, the power transistor should be replaced w/ your other unit.

good luck

 

I described it poorly. The Blower runs only when the ignition is on. But the blower motor runs on high regardless of the blower motor setting, including off.


So I was impatient and replaced the TCO in the second unit... Same exact issue. This time I had someone more competent solder it.


Do I need to take the same steps you described above?

 

Can you confirm you still have 1.5Kohms on 3-4 resistance check?

If yes, check w/ power transistor connected to system for voltage on wire 1 (blu/yel). If voltage stays at 12V for all fan settings, something is wrong w/ ATC as voltage should vary to reduce blower speed.

good luck