Heater blower issues

chillman88

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Hey all.

I got in my 91 the other day and the heater wasn't blowing on any setting. I started to move and it kicked on. Occasionally it will be working on high and then blow a lot harder or vise versa.

It sounds like a bad ground or short to me but I really don't know where to start looking for it.

When I bought it the blower fuse had burned up and been cut. I put an inline fuse in and got it working again. FYI when it wasn't working wiggling the inline fuse holder didn't make a difference.
 

chillman88

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Did you look at the blower motor resistor?

Sent from my SM-G892A using Tapatalk

Usually working only on high is an issue with the resistor, easy fix.

I did NOT check it because the issue is when it's on HIGH. I assumed if the resistor were the culprit then it wouldn't affect high at all. Last I knew all the speeds worked... when it works that is.

Did it again this morning. Let the truck idle 5 or so minutes before work, defrost on high. Pulled out of the driveway and the fan started blowing hard. I'll start with the cab ground when this darn rain stops. I read the blower is backwards so to speak? Power is constant and the control varies the ground?

Where are the cab grounds on these? Are they under the heater on the firewall in the engine bay like they are on my Chevy? I just need to know where to look.
 

Thewespaul

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I had an issue earlier in the year were my blower would act like it was getting debris in it causing it to slow down. You are correct that the ground controls the speed, and I fixed my issue by adding a dedicated ground for the blower right on the battery. Never had the issue again and the blower performed better than ever
 

chillman88

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I had an issue earlier in the year were my blower would act like it was getting debris in it causing it to slow down. You are correct that the ground controls the speed, and I fixed my issue by adding a dedicated ground for the blower right on the battery. Never had the issue again and the blower performed better than ever

If you wouldn't mind showing me where you ran from the blower I'd appreciate it. I was thinking about running a new power lead to it as well. Did you run the new ground AFTER the resistor or??
 

Thewespaul

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I just ran it from the ground coming out of the resistor, that way the speed control still functioned. I’m not near the truck at the moment but here’s some pictures from google:

This is the resistor I’m speaking of
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Here is a diagram, should be the black wire that you will ground
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chillman88

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First off thank you!

Second... why on earth would Ford run the entire current for the blower motor through the mode switch?! Probably the same engineer that wired up the headlights.....

I will probably put a relay in for the blower and then run a second ground from the resistor like you did. Thanks again!
 

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