Blower Motor Speed

[Meister]

My Mark was having an issue where the speed of the fan would randomly just be cut in half. I would have the fan on max (whether the auto had it to max, or I had manually put the fan speed to max), then it would just get it's power decreased by 50%.

The manual control would still function, but at HI I would only get what seemed to be 50% power.

Then one day the blower motor stopped working...

I searched and discovered the many threads about the blower harness being the issue...I pulled my harness, and sure enough the end where it plugged into the blower motor was very crispy.

I ordered a new one from Ford and installed it. The blower is always operative now, but I still on occasion get it reduced to 50% power...it seemed.

I then replaced the speed control module (the module that the blower harness plugged into).

No change.

I went on a 800 mile trip this weekend through hot Arizona. I had the AC on full blast the whole time (it was always nice and cold)...and the fan manually set on 'HI'. The fan speed would randomly go to 50%, I would make sure that the manual control was all the way up, and it would increase and decrease fan speed, but only give me 50% at the 'HI' setting.

I'd be cruising along, then it would go back to 100% for awhile, then go back to down to 50%.

Their was no rhyme or rhythm...just when it felt like it! I tried dropping the glove box and wiggling around the new harness on both ends while it was at '50%', no change.

Sorry for the novel, just wanted to explain my problem.

Any thoughts?

 

[driller]

Have you tried the EATC self diagnostic routine? It will test the electrical functions of the EATC module.

 

[Meister]

To be honest, no. I never thought it could be an issue with the EATC module itself.

How does one do that?

 

[J]

I remember when my buddies car would do that, and other make vehicles. I found it to be a vacuum issue and some of the doors in the box would not be open all the way. You should check the MAX A/C (recirculate) door that is attached to the blend door. Its not run by vacuum, but if its switching from MAX A/C to NORM A/C you could be loosing air volume. If you drop your glove box and look to the bottom left corner, you will see a gray arm with a metal flat rod attached. Pay attention to the position and once the A/C cuts down to 50% look at the position of the arm again. If its in a different spot, you may be having blend door issues. My Dad's 97 that I'm fixing right now had that gray arm actually break so it would not go to MAX at all.