Ok I have searched and read many similar problems but nothing exactly the same.
My 97 f-150 has a new heater core. The temperature control **** is not cracked it works.
When I turn it from hot to cold the speed of the air does not change. I can have the heater on and it will just randomly start blowing cold (with the temp **** all the way too the hot position.) Sometiems I can just barely back it off from all the way hot and it starts blowing hot again.

Where should I check and what should I be looking for?
How come if I change from heat to ac there is no change in the fan speed?

 

High speed is high speed, or 3, or 2, etc. You dont have a change in speed going to AC. If you go to MAX a/c you will get a change in sound due to the fresh air door switching to recirculated position and may feel a difference in airflow at the vents, but the blower doesnt change speeds.If the recirc door is inoperative, or the controller has lost function naturally you wont get the change in sound. A vacuum leak can cause such problem. You can also get a change in sound changing from hot to cold and back.
What you are describing could be a defective blend door actuator, temperature control switch, bad connection at either one of those, bad wiring, or a broken blend door. If the circuit has poor connection it can cause the blend door actuator to wander, as well as a bad switch, or bad circuits in the controller itself. If the door is broken the door can change position due to gravitational force during turns.

 

I don't know much. Where do you suggest I start looking and what do I look for? The change in airspeed that I am referring to is the one that should happen when I change from hot to cold.

 

In the center of the dash at the bottom is black plastic panel. remove it. You will then see the blend door controller, white colored plastic box about 1/2 inch thick and will have a white colored connector plugged into it. With key set to on, turn the temp control **** from hot to cold and back repeatedly while observing the shaft coming out of the controller. You will only see a small section of the shaft. If the controller is working you will see the shaft rotate about 1/4 turn either direction as you move from hot to cold. If it moves as described then the blend door is broken if you dont hear the change in blower sound or feel a temp change. It is pretty sad if you just got a new heater core because it is the same job to get to the plenum... full dash removal, plus air conditioning recovery, evac and recharge. This should have been something that could have been identified as a problem when the core was done if it just has been done....

I personally always advise the customer that when doing a heater core that I might find the blend door broken and give the plenum job into the estimate. And definitely anytime I do a plenum job I recommend a heater core and blend door controller at the same time to save the customer money in the long run.

 

I just did with out heat for a while until my heater core started leakin and steamin into my truck. I have a friend that is a mechanic at a local ford place I bought a heater core from NAPA and had him put it in for me. So its not like I went through the dealership or some repair shop I just told him what to do for me you know?
But I am taking final exams this week and will check what you are talking about asap.

Any other ideas?

 

Best bet is to have your ford tech friend verify.

 

After having a normal functioning heater/AC system for 6 years and over 100,000 miles, I started to get similar problems. Took it to the dealer and they replaced the temperature rheostat (F85Z-19C733-AA) and the motor (2L3Z-19E616-BA) for a parts cost of about $80; The kicker is the labor: $360! Since this repair was done, they have changed out 2 rheostats under some kind of "service warranty". The rheostat that is in there right now, doesn't feel right either. It rotates from cold to hot smoothly until the last 20 degrees or so of roatation, then it feels like I'm picking up a detent or something. I'm almost afraid to touch the temperature control anymore, afraid I'll wind up freezing to death in the winter or cooking in the summer.

 

For that kind of money you need to see the service manager and demand it fixed right before its way too long after the repair to hope for help. They obviously didnt fix the problem. I have never replaced more than one rheostat and rarely ever have to replace one. I think I have had maybe two bad ones in all these years.

 

[QUOTE=ferrofab] It rotates from cold to hot smoothly until the last 20 degrees or so of roatation, then it feels like I'm picking up a detent or something.

Sounds like somthing could be binding the temp blend door.