94 Q45 HVAC Blower/fan

[burijon]

In regards to this post about the blower motor for the HVAC; zerothread/193322 would it be the same remedy if your fan was stuck on speed 3 and will only go up to speed 4 but not below 3? The controls will move the LED readouts to full fan or only one fan blade full but still blow at 3 fan blades full. I'm glad it's stuck this way versus no fan at all really. I'm assuming I probably need a new blower motor? I was thinking it was some reostat or whatever the proper lingo is for controlling the motor. Could it be the controls in the dash themselves?
Modified by burijon at 11:02 PM 8/22/2006

[Q45tech]

Max speed is from a relay bypassing the transistor speed controller and sending full battery voltage to fan motor. Never seen one stuck in low speed either Normal, dead [motor], or max [speed controller].

However anything possible with HVAC ecu........does internal diagnodtic loop show any codes?

[burijon]

I haven't done any diagnostics yet on it since it just started yesterday. I did realize this morning that the fan continues to blow with the key in the ACC(engine off) part of the ignition and with the HVAC controls off. I'll try and read up in the FSM tonight of how to diagnose which relay is most likely bad. Thanks for your suggestions.

[elwesso]

it kinda sounds like the resistor could be bad... Still, do self diagnosis and see if it comes with anything strange.

[burijon]

Based on some more searching I believe it is the fabled darlington resistor. Q45Tech's answer is to replace both the blower motor and resistor because it's pulling to hard and getting hot and therefore in turn frying the resistor. I will try and source both parts. Thanks NICO!

Q45Tech"One must realize that the reason the transistor failed is that it was being overloaded beyond its MAXIMUM rated current/power by the load [electric fan motor 100watts]. Worn out slow turning fan motor just waiting for the right combination of heat and speed and duration to take out the replacement again and again.Not fixing the problem just temporarily covering up the symptom until the next failure."

ElWesso picture of darlington resistor. "Its the silver box thing in the middle."

[elwesso]

good job on searching.. I believe that if you clean the motor out you should be OK...

[Q45tech]

Why not measure the current under different speeds and temperatures to determine the reserve available in the transistor.......easy to calculate the failure point when current and temperature is known.

Remember the transistor is doing nothing at max speed [bypassed by relay] so 3/4 is worse case and heat in input air [from not recirculating-vent].

I plan on making engineers out of members even as they kick and scream and shout profanities.

[maxnix]

I plan on making engineers out of members even as they kick and scream and shout profanities.

Isn't there some way to let members "feel like" there's a difference and maybe drop the current a couple of volts so it looks cooler?

Numbers are so scary!

[elwesso]

Isn't there some way to let members "feel like" there's a difference and maybe drop the current a couple of volts so it looks cooler?

Numbers are so scary!