ATC/outside Temp problem

[dglossop]

Greeting fellow SHO Enthusiasts:
I have a strange problem. After cleaning the engine, the A/C would not work in Auto mode. MAX AC however did work. Just for grins I hit the outside temp and it read -40! This explains (I think) why A/C wouldn't work in Auto mode. I assumed a bad temp sensor so I took the sensor of my other SHO and plugged it in and still got a bad reading. I put the "bad" sensor on the other SHO and got a good temp reading. Thus the sensor is obviously NOT my problem. Any ideas???
Some more details: The temp outside reading is either crazy cold (-40 to -20) or crazy hot (110 or more). When it is reading high the A/C works perfectly normally but when it reads cold it only works in MAX AC mode.

 

[hawkeye18]

One of the "features" of the EATC is that it will not engage the compressor in "AUTO" under about ~55 degrees F. the reasons for this are fairly obvious (unless you think 40f is warm!) but the end result is that while your sensor reads -40, well, that's under 55, so no compressor function. It works for the same reason while it's reading 110.

Which sensor did you change? The sensor you are referring to is right in front of the condenser, behind and a little to the right of the ford oval, mounted on its own little bracket. If you changed the sensor that was in the air box, that's the one that tells the ECU what the intake air temp is.

Let us know if you got the right sensor and we can go from there.

 

[dglossop]

Hi and thanks for responding. I have the correct sensor. I was aware of the below 55 rule which is why I was attributing the lack of A/C with the super cold temp reading. However, I was not certain that there was not a different temp sensor that would control that feature. If we are correct, some smart engineer configured the system to allow the compressor to run in MAX AC mode regardless of what the temp sensor was reading. For that I am very glad since the car is still drivable in hot weather as is.
OK, so now you know that I changed out the correct sensor; next suggestion???

 

[Rockledge]

Have you tried the EATC self-test? Maybe you'll get a code back.

 

[hawkeye18]

well, -40 is about as low as that sensor will go, and 120 is as about as hot as it will go (yes, I've seen it higher [142!], but not very often), which kinda tells me that the wires (all 2 of them) are alternately opening up and shorting out. Unfortunately, this means you have to go wire-chasing. Which sucks. I hate chasing wires, and I do it for a living...

In any case, you'll need to figure out where those wires go - (ultimately) to pins 1 and 2 of the EATC, the connector on the right as you look at it from the back. The wires will be red/orange and pink/black, and they'll be next to each other. Have a friend put a multimeter on these wires while you wiggle/twist/etc. the harness that they are in. Hopefully you will find a spot that makes something change... that's where you look first. Good luck!

Also, do the self-test procedure: press the "OFF" and "FLOOR" buttons simultaneously, then within 2 seconds press the "AUTO" button. If the test is successful, after about 20 seconds (or longer) every LCD segment will light up (the "888"). If the ambient temp sensor shows bad to the EATC as it obviously shows bad to you, you will get a code of "04". If you get the 888 or any other code, let us know.

Press the blue (temp down) button to exit the test.

Edit: right, the procedure had already been posted. My bad. Another thought is that you could disconnect the wiring at the sensor and check for +5V (or +any volts) while wiggling.

 

[dglossop]

Thanks again for the info. I don't understand what you are saying "my bad" about; I appreciate you going thru the EATC self test procedure as I am a novice forum user. Please just clarify one thing; am I suposed to see 5v at the sensor and I should be looking for a voltage drop while wiggling?

 

[hawkeye18]

well, while the EATC is on, that sensor should be getting 5v. if you're seeing 0v, there is either a short or an open, cos either way voltage isn't getting all the way to the sensor plug. So start by wiggling the plug itself (the pins can get corroded and break inside), then wiggle/jostle the harness about every 6 inches to see if you can find where it's breaking/shorting.

 

[SolidState]

I had the plug fail on my temp sensor. New harness spliced in and all was good...

FWIW, the sensor and its harness are the same as a the ECT. I pulled the harness from a gen2 3.0L vulcan motor.

 

[hawkeye18]

I had the plug fail on my temp sensor. New harness spliced in and all was good...

FWIW, the sensor and its harness are the same as a the ECT. I pulled the harness from a gen2 3.0L vulcan motor.

I think you mean IAT? I'm thinking an ambient temp sensor would not last long in hot coolant...

 

[SolidState]

no, I mean the outside temp sensor and the Engine Coolant Temp sensor are the same part.