Faulty External Temp. reading causing A/C to stop

[krmcginnis]

I have a 2003 EB Expedition 5.4, when I bought it the ext. temp reading on the a/c module was off, about 30 degrees below in the summer and about 15 below in the winter......no big deal I thought but over the years is has gotten worse and now when the ext. temp drops below 28 degrees the a/c stops putting out cold air. The readings are all over the place......upon starting the car it usually has the correct ext. temp showing but once you start driving it will drop, sometimes just a couple of degrees, other times it will drop 50 degrees in about 15 sec., read as low as -40. At some point it will start to go back up which is a slower process but once it reaches 28 degrees the compress clutch starts back up and the a/c works again. I've changed out the ambient air sensor last summer and that appeared to help for a few months, got me through summer anyway, but it was always still off 20 degrees. This year it keeps dropping fast and again once below 28 degrees an no cold air anymore -- I live in Dallas TX, heat is coming this way......changed the a/c control module out thinking that might fix it but still have the same issue. Anyone have nay ideas? I really do not care if the ext. temp works, if I could rig it to read anything above 28 degrees all the time I would be fine with that as the a/c would work. Every shop I have taken to tells me it's the compressor within about 2 minutes, I really do not think that is the case, ice cold when working and ONLY stops when the ext. temp display drops below 28! Annoying to say the least.

 

[Hamfisted]

If you pop the plastic shroud off that covers the radiator top area, on the passenger side, near the headlight, you will find the exterior ambient air temp sensor. It's about $22 from Rock Auto if you want to replace it. Was the Expy wrecked in the front end that you know of ? Lotta times that sensor gets busted in front end collisions. See what yours looks like. It's easy to replace.


Outside air temp sensor ....


https://www.rockauto.com/en/catalog...ditioning,ambient+air+temperature+sensor,7000

 

[krmcginnis]

Already replaced it, twice, just in case the 1st one was defective. 1st one helped but did not fix, second picked up where the the 1st left off. Car Fax shows no accidents reported.

 

[Hamfisted]

What's it read if you unplug the sensor ? Has anyone done any work behind the dash? Like an aftermarket stereo or anything? The sensor is just a thermistor (temperature sensitive resistor...) so if you've tried a few new ones it sounds like it's a wiring issue. Do you see any damaged spots in that harness ?

 

[krmcginnis]

Original radio, replaced the A/C control module and wiring looked good, wiring on ambient air sensor looks good but I have not followed it all the way through. Have not looked to see what it reads with sensor unplugged, I'll give it a try tonight.

 

[Flexpedition]

Did you happen to use a genuine Ford part on either replacement?
AE5Z-12A647-A

I'm on a couple F150 forums and recall threads with the exact same issue -- where generic, Amazon, ebay, etc. Chinese sourced sensors either are DOA or have a very short life span. Replacing them with the twice as expensive Motorcraft version solved the issue. Good luck either way.

PS - Use to work in Richardson in the Campbell Creek area. Wish I bought real estate around there 20 years ago...

 

[krmcginnis]

It's a Duralast sensor -- maybe I'll try a OEM, have not seen anything along these lines that actually cuts the a/c off due to ext. temp

 

[Hamfisted]

Mine works normal in my Expy ('03) and unplugged the EATC display shows an outside air temp of steady 50 .... if that helps. Why did you replace the EATC head unit ?

 

[krmcginnis]

Took out the Ambient Air sensor and that makes the ext. temp read 50 degrees steady, so that will fix my a/c issue! Thanks!

 

[WISIV]

I don't know if this will help. I have a 2000 mercury sable that I was having trouble with the auto lights. The auto light sensor is on the dash by windshield (little plastic hump that flashes). Believe it or not this little sensor controls auto lights, but was also tied into the EATC.
The mercury also has a external temp sensor. When I replaced the light sensor on dash with a ford part, the EATC had to be reset by pushing and holding certain buttons on the EATC, which would give trouble codes. You have to reset the EATC. I'M sorry I don't remember which buttons I pushed and held, but all of this seems to be tied into this ambient light sensor on the dash. It may be similar on the expedition. I had to replace the whole EATC on my wife's expedition after a screw got inside of it and shorted it and the blower motor relay out. Good luck I hope this helps and applies to you situation. I found the information to reset the EATC on the net.