EATC Fan Speed Erratic.

[ByronRACE]

Can anyone tell me why my AC/Heat fan speed is irregular when set to anything other than maximum speed using the wheel to the right of the EATC?

If I set it to max, I hear a relay click and it's on high speed and consistent. If it's set to any other speed, the fan speed varies intermittently and will jump to anything between full speed to low speed...and it seems to change when I hit bumps in the road. It never turns off. When it picks a new speed, it just goes to that speed nicely and stays there.

If I had to guess, I'd say the cabin temperature sensor or circuit is misreporting the interior temperature or something like that.

Self test passes with no faults.

Has anyone seen this?

Thanks,

Byron

[yjmud]

THE BCM IS FAULTY MOST LIKELY

[Logizyme]

when you select the fan speed using the wheel the EATC does not control the fan speed based on cabin temperature - so you can forget the cabin temp sensor.

Based on the description of your symptom it sounds like the switch is erratic. I've seen blower motor resistors fail several ways, but never have I seen them erratically change speeds on its own.

Either way your top two things to look at are the EATC(and its build in speed wheel switch) or the blower motor resistor.

good luck.

[ByronRACE]

Thanks guys, I dug into it last night and resolved it. The BCM (as yjmud suggested) was faulty, again. 150K miles (or so) ago, the fan died completely and I took the BCM out and found that the solder joints on the main big power lugs was cracked. I soldered that, and it worked fine until now (near 200K miles). This intermittent fan speed issue was another cracked solder joint; this time on one of the smaller pins on the same connector. I cleaned off all of the solder mask to bare copper around all the pins this time, and soldered the hell out of everything. This morning, the fan operates normally. Sorry the pictures aren't better; I took them for myself...didn't think of sharing them until now.

http://www.racesystems.com/temp/bcm1.jpg
http://www.racesystems.com/temp/bcm2.jpg

[fastblackmerc]

Common panther-platform problem.

[jwibbity]

guess I'll be pulling out my BCM, I have a similar issue but I only get full blast only. It shuts off fine but the dial on the EATC is useless right now

[yjmud]

I AM GLAD YOU GOT IT FIXED

[ByronRACE]

guess I'll be pulling out my BCM, I have a similar issue but I only get full blast only. It shuts off fine but the dial on the EATC is useless right now

When my BCM failed the first time, I would intermittently lose the fan completely. Not a speed problem; it would shut off completely. It would not even function with the wheel at the max setting. That was cracked solder joints on the two large terminals in the BCM at the connector. The intermittent speed problem was the solder joints next to it that I didn't have the foresight to reinforce; they failed many years later.

[gatlandc]

I have this blower issue too; I posted a comment earlier under http://www.mercurymarauder.net/forums/showthread.php?t=100629

I guess I will pull out the BCM and check the soldering...