Problem with HVAC blower

[mrmopar5287]

I've got a 1991 Legacy that is having some intermittent trouble with the HVAC fan.

Whenever I start the car and the HVAC system is already selected some kind of ventilation, I have no trouble with the fan or temperature controls. All temps and all fan speeds can be switched back and forth.

Whenever I change to a different HVAC mode (such as switching from Max AC to regular AC) the blower fan will frequently cut out and will not be able to be restarted until switching the HVAC system off for several minutes. Sometimes the car has to be completly shut down for several minutes before the blower fan will restart. This problem started several months ago, and has become more worse as hot weather has set in and the air conditioning is being used more.

I took the vehicle to the dealership where the technician replaced a fan relay and cleaned all the contacts and circuit boards inside of the HVAC button selection panel. The technician told me that the climate control module needed to be replaced, at a cost of $320 for the new part. I got a used one on Ebay for $50, and this used part did not fix the problem - the same symptoms occur.

Does anyone on this message board have any suggestions, perhaps from experiencing the same problem? The dealership technician did a lot of wire tracing and found no short circuits or loose connections. He noted that the blower motor appears to be newer, but I suspect that even if it is a newer part it might have some intermittant fault inside of the blower that is not detectable. Anyone think they can help me with this problem? I don't care now that it is summer time - being without AC I can handle. But I really need to have this fixed before winter, because I simply can't be driving a car where I cannot switch between the defrost modes to keep ice off of the windshield.

[IronMonkeyL255]

There are a few threads out there about this.

A search will yield some results.


I had the same problem before.

It turned out the be some of the solder joints de-soldering from the board. The reason the speed selector and temp. sliders still work fine is because they aren't even connected to a board (the speed slider is just a switch straight to a connector, and the temp. slider is attached to a cable).

To fix it, I just took the HVAC unit out and re-soldered the connections.

Now it works great.

[mrmopar5287]

I will give that a try. For your re-soldering, did you simply touch the iron to the connections to have a little bit of melt secure the connections, or did you completly remove pieces from the board and redo them completly? How can you tell which connections need to be resoldered - is this work that I should use a magnifying glass?

I have a nagging suspicion that the problem is something else. The technician replaced the resistor, but it seems to be too much of a coincidence that a second HVAC control panel would have the exact same problem without at least a short period of time where I might experience perfect operation of my HVAC system.

[free5ty1e]

Those are called "cold solder joints" and are improperly soldered at the factory. Happens all the time, with consumer electronics too (TVs and such). Cold solder joints are formed when the solder is melted by the iron and cools on the joint instead of having the joint itself get hot enough to melt the solder - which is what you'll have to do to fix any cold joints.

You can find them with a magnifying glass. They should look noticably different than the good solder joints.

[mrmopar5287]

Alright, I took the HVAC control unit apart, took the circuit board to an electronics shop to have all the connections resoldered, and the same problem still exists. My next try at fixing it will be to replace the blower motor relay - even though there aren't normal symptoms of that being the problem. Does anyone else have any suggestions? This is driving me absolutely crazy . . .

[mrmopar5287]

Bumping this back to the top. It's been a long time, and new hot weather has the problem getting worse.

Does anyone have any suggestions about knocking together my own manual fan speed controller? The blower motor works fine, so I basically want a dial controller that I can mount on an empty spot on the dashboard to turn up or down the fan speed. The HVAC control panel still works fine to control the AC compressor, and the ducting of intake air. All I need is fan speed control. Any electrical engineers out there that can help me out?