It's getting pretty hot here now and I've ignored this problem for long enough. When I have the AC going it's plenty cold but the air doesn't come out fast enough to cool down the cab. Before I going tearing things apart does anyone know of any common issues like this with these trucks. I have a 96 F-350 Crew Cab w/5.8L. When I have the fan on high it come out more like what I'd expect medium to be.

 

I think there is a blower motor resistor that controls fan speed. It's typically located below the glove box. You'll see a wire harness hook directly into the heater core casing- right where it hooks up you should see a couple of screws. Remove the screws and the resistor should come free.

It's typical for them to fail due to corrosion.

 

so is it just the fan that you feel has gotten slower or do you here the fan the same speed just not so cold?

 

Gauging from the sound of the blower motor and the amount of air coming through the vent the fan seems to change speed fine. It's just that high doesn't really seem like if blows very hard. I've had this truck about 4 years and it's always been like this. One other thing too. When I put the AC on max and open the throttle all the way up the fan stops blowing all together until I let up on it. I thought I had a vacuum leak but I've changed every vacuum hose that I could get to. Plus the truck seems to idle normally.

 

The fan may be changing speed just fine, but if the resistor, which controls fan speed, is going bad, then it stands to reason that you would experience problems with the fan speed. In other words, if the "high" setting doesn't seem like it's blowing air as fast as it should be, then that's an indicator that the resistor is going bad.

The only way for you to know for sure whether or not the speed on your blower motor is correct is to find another truck that's the same year as yours and see how well that air blows. Of course, asking another Ford truck driver to blow his A/C for you might not yield the results you're hoping for...

 

But seriously, this is what I'm talking about...

Motorcraft YH1720 - Blower Motor Resistor | O'Reilly Auto Parts

 

10-4, seems like the local store has one. I'll go grab one tomorrow and put it in. Thanks for the help.

 

When the resistor fails you're only left with high.
All the other speeds are controlled by it, 'high' is full (direct) power.

Pull the blower motor out of the plenum.
It is only a few screws.
Sometimes leaves and other debris build up on the inside of the squirrel cage.
While you have it out, look inside the duct work for other junk.

The evaporator core can get clogged up too.
Do you notice the lack of flow when the climate control is set to heat?

Losing the vents at WOT usually means there is not enough vacuum to keep the door in the proper position.
The default position is defrost.
Next time it does this, reach up to the bottom of the windshield and see if the cool air is coming out there.

What temperature is the air coming out?
Have you checked the charge in your system?

 

Jim is right, the resistor network has nothing to do with high speed blower. If you check voltage to the motor with it still connected and have within .5 volt or so of battery voltage, and nothing seems to be clogged, I'd try a new motor.

 

the blend door could also be jammed by something falling down the duct causing it to mot close completely.
i had the same problem on the 96 F-superduty last year.
popped the heater core out and broke the blend door free, now it works like it should.

 

Thanks, ArdWrkntrk, all fixed. It ended up being a clogged evaporator. I took out the fan and felt around against the face of the evaporator. It had fluffy coating, of I don't know what, all over the face of it. I hosed it out and ran compressed air through it. Nice hard blowing cold air now. Also I found a vacuum leak on the tiny hose going to the max ac door. Thanks for all the replies.