2000 Ford Windstar A/C won't turn on

FRYEMAN

MEMBER
2000 FORD WINDSTAR
6 CYL
FWD
AUTOMATIC
104,000 MILES

Good Morning, My A/C compressor on my van won't turn on. They tell me the freon is full, that the PCM turns on the compressor in "test mode". Both places I have taken it to are continuing to look for the outside air temp sensor. They get a B1254 code (air temp ext snsr failure). No one can seem to find the sensor. My questions: 1) I don't have an indication of outside air temp inside the vehicle. So would I actually have an external air sensor? It's supposed to be located behind the front bumper and no one can seem to find it. 2) If the IAT was bad would that cause the A/C not to turn on due to the sensor showing a cold temp? And isn't the IAT part of the MAF sensor?

Thanks, Rodney

7 Replies

MERLIN2021

MECHANIC
17,250 POSTS

Top is 3.0 Bottom is 3.8 Iat= Intake air temp, not the same as AAT= ambient air temp! 3.0(top) it is at #22, Bottom(3.8) it's at #25
IAT= Intake air temp
AAT= ambient air temp, not the same! AAT is what your looking for!

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Tuesday, July 7th, 2009 AT 8:58 AM

FRYEMAN

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4 POSTS

I have all of that. But is the AAT the sensor that can keep the A/C from coming on? Or is it the IAT sensor? And, do all vehicles have this AAT or is it possible that it really doesn't exist? The vehicle hasn't been in a wreck so no one has forgot to put the AAT back on. The A/C worked at the end of the season last fall (November 08) but now won't turn on. The 2 A/C repair places seem to be chasing their tails on this and have now had the vehicle for 2 weeks total and can find nothing. My question is which air temp sensor, (AAT, IAT) controls the A/C? Or what else could possibly be causing this lack of A/C?

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Tuesday, July 7th, 2009 AT 9:09 AM

MERLIN2021

MECHANIC
17,250 POSTS

Yours has it, and the IAT will not prevent the a/c from working, have them bypass the low pressure cutout switch as a test, does the compressor run?
A defective AAT that is showing a code can give these symtoms.

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Tuesday, July 7th, 2009 AT 9:21 AM

FRYEMAN

MEMBER
4 POSTS

So the low pressure cutout switch is in parallel with the AAT? Jumpering out one will effectively get both out of the circuit?

The code (B1254) will not come up unless it is real is that what you are saying?

If all of this is true then where in the world could the AAT physically be located? They even took off the fron bumper and said they couldn't find anything. Two places said this. Any ideas?

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Tuesday, July 7th, 2009 AT 9:36 AM

MERLIN2021