I have a 98 F150 with an a/c problem. It starts out cold and as you are driving the cold air turns hot. Not vent warm but as if the heat is coming on. Any ideas on what would cause this? Is this a blend door problem? Thanks for any info.

 

Pretty likely.

Steve

 

i would check the tubes into and out of the compressor and see if one is cold and one is hot????? the blend door is electric controlled and positioned by the temp **** on the dash. if it has a problme it sometimes sticks or will not move, but it should not change when driving down the road?

 

I would definately say that it is not a A/C charge problem. If the A/C looses its charge, it will just get warm, not hot. It was my understanding that the blend doors are vacuum actuated. I remember on my Super Duty (when I had it) I was having a problem where the heat would change to the defrost, which is the default when I was going up a hill. Turned out to be bad vacuum line. I would definately check the blend door that controls the heat, not the air flow.

 

dont forget to check the vacuum lines under the hood near the heater box

 

there are three ***** on the heater dash panel, the center is the temp control and it feels like a variable resistor when you turn it. it is sending a voltage signal to a motor that controls a blend door. the door mixes hot and cold air at 0-100% depending on the settting of the ****. this gives instant temp changes when youu move the **** and dont depend on turning the hot water lines on and off like old days.-------- the defroost- panel- floor **** is vacuum controlled and is "on" or "off" depending on which way to stroke the vacuum cylinder. two cylinders, one picks defrost or floor, the other pickes panel-floor. if you loose vacuum the default to to go to defrost position.---- if you are changing temp, you are talking about the electrical motor- blend door. if you are talking about which vent it is coming out- that is vacuum.

 

Interesting. The temp control on my 98 starting acting up this past spring when I was doing alot of temp changes, i.e cold mornings and hot afternoons.
When gradually cranking it from hot to warm to max cool the air temp wouldn't change. I'd have to crank the dial to max heat then back to max cool to get it to change. I figured either the blend door or cable/mechanical linkage from the dial to the door was binding and I'd get to it come fall.
Well now it seems that it's not a mechanical connection between the dial and door but an electrical control for a motor on the door?
Hummmm. If so then I'd suspect either the variable resistor has some sort of deposit thats insulating the contacts ( like what dust did to old timey audio volume controls) or the linkage between the motor and blend door is binding.
Since I stay in max cool now I haven't bothered with it but now I may dive into it and see whats what.
Seems I noticed this problem about the same time that a couple of my dash lights went out.
I can't complain too much as it's been a very good truck for me for 8 yrs.
Volfandt

 

I have a 2001 Super Crew. The blend door motor/actuator is located at the lower portion of the air duct under the instument panel (dash) and is in the ideal position to drain water out of the air duct "IF" the condensate drain is plugged. Water will drain into the plastic motor/gearbox and internal printed circuit board and cause the control of the blend door to be erratic or lost. Make sure your condensate drain is open. I removed my motor/gearbox and dried it and drilled drain holes and reinstalled and have no further problems. It is a rather large chore to remove the motor/gearbox actuator due to it's location. I had to remove the entire dash! Hope this helps.

 

Well I bit the bullit and pulled the dash. The blend door was broken at the bottom where it connects to the motor. The door had a new ford part number so I hope there has been a change in this one for the better. A days work and about $40 dollars its fixed. If your truck has random temp changes and the temp control **** does not respond this may be your problem. Good Luck!! Thanks to everyone for your input.