'98 F-150 X-cab V6 manual everything (windows, tranny, locks.)

I get AC at every setting except "off" and "panel", regardless of the setting on the temp control. With the temp control full clockwise (red zone)the compressor comes on and I get ice cold air. If I set the other **** to "floor" I get ice cold air on the floor, etc. It's as if the controller (however it's done) doesn't know where the temp contol is set to.

My question: Is the temp control a variable resistor read by a microprocessor ? I could understand if the heater control valve wasn't working (vacuum leak or something) but this double trouble has me confused...the ac doen't turn off and the heater control valve doesn't come on.

I'm an EE so feel free to include the bloody electrical details if you've got 'em.

Thanks,

Shivering Mark

 

Shivering,
The a/c should be on in the positions you indicated. It sounds like your heater core isn't getting engine coolent to heat it. There is probably a vacum or electrical valve in the heater hoses somewhere that isn't opening. In the older Fords, the temp control was a mixer flap that mixed cool air with heated air. I'm not sure in the new ones--never had any trouble & the Chilton's doesn't go into it.

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97 Lariet-sc-4.6-4x off road-auto-3.55 LS-
superchip-K&N-3"
pvc air box mod-Granetelli MAF

 

MarkF - A/C should not run in 3 positions. They are: Panel, Off, or Floor.
Air flow is always through the A/C evap core (whether A/C is running or not), then to the heater core area, where it may bypass the heater core, run through the heater core, or a mix of flow through the core and bypass. The mix is determined by the Blend Door. Hard one way, it blocks off the airflow into the heater core, hard the other way, forces it all through.
The Blend Door Actuator has 5 wires: Ground, 12 volts from fuse (your fuse must be good, as it also provides power to the A/C clutch through the selector switch and pressure switches), 3 wires from the Blend Door Pot (the temp. control).
The temp control has 3 wires as expected for a pot. No processor, luckily.
Didn't see anything on a heater shut off valve. Maybe I missed it. Seems there would be one, to get Max A/C effect.

 

Grandpa,

Thanks for your reply. What's wierd is that on "floor" the compressor doesn't turn off. Is the Blend Door Actuator responsible for controlling who's on and who's off ? Or is it the controller that moves the door that directs the air to the floor or the windshield or the panel or the combinations of the three ?

RedLariat indicated that the ac is on when the heat is on, and you said that you didn't see anything to turn off the heat when the ac is on, so based on that I would think that everybody is on all the time and the Blend Door Actuator is the man that determines the temp. Sounds funky, but ya' gotta admit, it would be simple (but inefficient). Looking forward to more feedback, we got the "warning cold front" this week.

Shivering, but closer, Mark

 

Mark
I looked through the Chiltons again & info is scarse. Try warming up the engine & carefully grab one heater hose then the other. They are the small 3/4" hoses at the passenger side rear of the engine. If they are both fairly hot, the coolant is circulating through the heater core & the prob is likley in the mixer door area. Grandpa may have got it by discovering the sensor on it I didnt know about. I think the drive is vacum. If one hose is a lot cooler, you have a bad heater core or there is a valve somewhere not opening. Good Luck

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97 Lariet-sc-4.6-4x off road-auto-3.55 LS-
superchip-K&N-3"
pvc air box mod-Granetelli MAF

 

If the A/C compressor is on when Selector is at Floor, I would suspect the electrical switch part of the Selector. That switch enables power to the compressor clutch through the High Pressure Cutout and Cycling Pressure Switches. In Floor position (not Floor & Panel, that's different!), there should be no continuity through the Selector switch for the A/C comp. feed.
Probably a good idea to look under the hood, and make sure that the compressor clutch turns off in at least some position, in case the clutch itself is stuck ON, regardless of power to it.

The temp. control only controls the Blend Door Actuator, which varies the amount of air bypass around the heater.

Switching of where the air flows out, like Defrost, panel, floor, and control of the air input door (outside or recirculating input) is performed by vacuum motors working doors. The vacuum to which vac motor is controlled by the vac switching part of the selector switch.

I don't think there is a heater shut-off valve in these trucks (when used, they turned off water flow to heater core when A/C was set to MAX, to insure maximum cooling by not having a hot heater core inside).

A rough check of hose temp like redlariet said is certainly worthwhile, but good luck getting to those hoses on the new style trucks. They are at the back of engine, under the overhang, at least on the 4.6L V8, don't know about the V6.

Did you have this truck last winter, and know that it worked properly once? I have seen some stuff totally messed up on cars and trucks that were bought used (and some not installed properly new at the factory!). I won't knock buying used, sometimes people give up and sell because of all the cash they have poured in to it to have a "professional" fix a problem, and the prob. never was solved. The next owner troubleshoots it with an open mind, finds and fixes it, and all is fine.

[This message has been edited by Granpa (edited 10-12-2000).]

 

Thanks folks...I'm diving in Saturday. Armed with the right info it will be a piece of cake.

If I can help out on general purpose electronics questions (I'm not a '150 expert) email me at mfossler@cfl.rr.com.

Hey Grandpa, I got'ta wonder about that "handle". You know a lot about the newer trucks............and thanks.