Hi, I've been lurking here a bit. I used to be on the 57-60 forum quite a bit, but the truck in my avatar has since been passed on to my brother. Anyway, I recently bought a 1989 F250. It's the light duty model with the Mazda 5-speed, semi-floating rear end and D44 TTB front end. It has the 5.0 Liter motor. It's a pretty clean and straight Nevada truck and it runs great. It needs some attention here and there. Right now I'm trying to get the AC fully functional. The system is charged and seems to be sealed and I can feel cold air at the vents, but the blower motor isn't working properly. The fuse is good, the evaporator core is clean and the vacuum lines LOOK to be OK as far as I can tell...

Here's my first question: if the resistor pack for the blower motor is bad, should the blower still run on high speed?

Thanks for any help in chasing this problem down...I'm sure to have a lot more questions!

Here is a picture of the truck...

 

Nice looking truck, you guys live outside the rust belt got it good!

Usually only get "High" with a failed resistor, other problem is the connector to the resistor the connections in it corrode turn green etc and if so blower doesn't work at all or just a little bit regardless of speed selected.

I'd pull the resistor out look at it a minute, tends be reality obvious when any one aspect of one is toast and will no longer function.

Replacement pigtail is also available if find that to be a problem.

 

Thanks Dan. I already pulled the resistors and they looked a little cruddy, but not really that bad. It's kinda hard to see how those things would even go bad, they're just coils of wire, but I guess they do. I just jumpered the blower motor to the battery and it works fine. So I guess there is a lack of continuity somewhere...now to just find out where. How do I test the resistors? I used my multimeter, set on OHMS and probed both ends of each resistor. I got readings of .005, .006 and .022 I think. Is that the correct way to test a resistor? Does anyone know if those readings are good? Thanks!

 

OK, with key on test light indicates power in the pigtail connection to the blower motor. so I guess the next place to look is my 4 position switch in the dash?

 

Yea coils of wire and if burnt its usually obvious as section of the coil/s would be missing.

Not sure what the values should be but if they have continuity through each one it should be good.

Don't over look possibility your switch might be bad, haven't had one fail myself yet but not much doubt somebody has by this point!

Not sure what you mean by "I can feel cold air at the vents" but if that is when the truck is in motion that'd be normal, little air without fan doing a thing.

Sounds like you gotta little bit of testing to do narrow down the problem, as with most anything couple ways to do it just depends on how wish to go about it and what ya have to work with.

"High" doesn't go through the resistor, goes direct from switch to blower motor, so if you don't have "high" then no the problem isn't gonna be in the resistor.

Do you need a wiring digram?

Battery power is direct to the motor via fuse #9, the grounding path is provided by the fan switch speed selections, and those lower than "high" speed via those resistors.

 

Looks like I found the problem. The harness connection for the blower switch is fried!



...unfortunately, I created another one. While I was disconnecting the switch, the sliding vacuum mechanism to operate the doors broke off and a small ball bearing fell out. I have it back together, but I have no idea where the ball bearing came from...




Does anyone know the proper name of the door positioning mechanism in case I need to order a new one?

Thanks for your help Dan!

 

I found the part on "wholesaler closeout" at Rock Auto...cheap! It's called a heater blend door actuator, which makes perfect sense. Hope this helps someone else.


https://www.rockauto.com/catalog/mor...381&cc=1124277

I'm having a real hard time locating the harness side of the blower switch though. There are plenty of blower switches available, but I can't find the female side anywhere on the web. Is there any good reason not to diagram that thing, cut it off and crimp on insulated female spade connectors in its place? It's either that or go the junkyard route...

 

The new parts are in and the AC is blowing through the dash vents! I did have to cut the harness and crimp on some female connectors. Autozone had the male side of the blower switch.

 

Got to love some AC...............
nice truck.........