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A. Penland
A. Penland, Ford Senior Master Technician, ASE
Category: Ford
Satisfied Customers: 6531
Experience:  ASE Master Certified, ASE Advanced Gasoline Engine Performance
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Explorer: 2013 Ford Explorer base, AC compressor wont come

Customer Question

2013 Ford Explorer base, AC compressor wont come on, had freon checked, it is OK... Outside air temp shows -40 degrees F. I changed out the AAT sensor, no change
Submitted: 1 year ago.
Category: Ford
Expert:  HDGENE replied 1 year ago.
Hello, so the outside temperature still read - 40 degrees? Does the engine cooling fans coe on when you command the ac to on? Has the vehicle been in an accident or had any add on accessories recently put on then this problem occured? Any codes stored in the Powertrain control module or HVAC module?
Customer: replied 1 year ago.
The car was in a accident, The cooling fans do not come on, and OBD2 reader says no codes
Expert:  HDGENE replied 1 year ago.
Ok thats what I was thinking, some sort of accident happened. Has the vehicle been repaired and still having this issue? Where was it hit and how bad?
Customer: replied 1 year ago.
front left, fender bender and is now repaired
Expert:  HDGENE replied 1 year ago.
Ok something else must be an issue in that area, either a loose or broken ground wire, electrical issue. Ideally the HVAC module should be checked with a scan tool to see if the ac compressor is getting a signal from the control panel to turn the ac compressor on. Maybe an issue with the ac relay in the power distribution box for instance. See if the cooling fans work when the engine reaches operating temperature. They should come on when fully hot besides when the ac system is demanded on.
Customer: replied 1 year ago.
One came on when the engine warmed up
Expert:  HDGENE replied 1 year ago.
Ok so you know the engine cooling fan is working. when it gets a demand to turn on the ac both cooling fans should run. You would need to look at the hvac and pcm to see if the ac is being commaned on when it is turned on first.
Customer: replied 1 year ago.
I have a OBD2 reader, Can I use that to diagnose?
Expert:  HDGENE replied 1 year ago.
The code reader will only look at the engine computer for codes, you need a scan tool that can monitor live sensor data and communicate and do the same with the HVAC climate control module as well
Customer: replied 1 year ago.
So this is not a DIY project?
Customer: replied 1 year ago.
Do you have a wiring diagram for the headlight harness? The harness that the Ambient Air Temp sensor is in, by the radiator
Expert:  HDGENE replied 1 year ago.
I dont think it would be and since its part of an accident, probably get it fixed for free in a shop through insurance if you made a claim. Give me one minute
Expert:  HDGENE replied 1 year ago.
I dont have a schematic showing how the harness looks sitting under the hood. Wiring diagrams are shown in manuals in different sections drawn out how they run. If the harness looks damaged it should be taken apart and damaged. A negative 40 degree reading usually indicates an open sensor. This is the same type of reading when the evaporator temp sensor fails.
Customer: replied 1 year ago.
I was wondering where the 2 AAT sensor wires go so I could check for continuity
Expert:  HDGENE replied 1 year ago.
The yellow violet wire is spliced from other sensors as its power supply and the yellow green wire goes back to the pcm as the input
Customer: replied 1 year ago.
So I should have 12v on the Y/V? do you know what pin Y/G shows up on in the PCM?
Customer: replied 1 year ago.
Any idea what fuse the power supply comes from?
Expert:  HDGENE replied 1 year ago.
The yellow green wire goes to connector C175B on the PCM pin number 17. There should be battery voltage to the temp sensor from what I can tell. It shares the same voltage supply for the ac pressure transducer on the high side line and many other pcm sensors
Customer: replied 1 year ago.
I have 5.1 volts on the Y/G and nothing on the Y/V???
Expert:  HDGENE replied 1 year ago.
Pin 17 as I mentioned. Something isnt right there. sounds like the circuit is being backfed. Its not one direct fuse a I mentioned. If that was the case you would have multiple engine codes
Customer: replied 1 year ago.
Also have 5.1 volts on the Y/G at the AC pressure transducer also
Expert:  HDGENE replied 1 year ago.
The yellow green wire to the pressure transduder is a different circuit, it is VREF which should be 5 volts. the yellow violet wire is shared for the pressure transducer and temp sensor.
Customer: replied 1 year ago.
This car was built in 5/2012... But is a 2013... Could there be a different diagram?
Expert:  HDGENE replied 1 year ago.
No, unless there is an error with the ford websites publication. Thats all I can tell you based on the information you are giving me.
Customer: replied 1 year ago.
The body shop said there was a change in a lot of the parts in 10/2012... Could you send me the diagram?
Expert:  HDGENE replied 1 year ago.
why dont you send me the 17 digit vin number, this is dual zone eatc?
Customer: replied 1 year ago.
Single zone 1FM5K8B86DGA62383
Expert:  HDGENE replied 1 year ago.
Hmm this vehicle has a branded title? Just a little fender bender?
Customer: replied 1 year ago.
Yep, Fender, hood, bumper and an aitbag
Expert:  HDGENE replied 1 year ago.
Well thats all the information i can give you, Im going to opt out and se if another expert can assist you. Anytime a vehicle has a branded title is usally an indication of it being in a major accident and it voids all warranties.
Expert:  A. Penland replied 1 year ago.
I need to make sure you are checking the proper wiring and sensors. We have seen issues with the Evaporator Temperature Sensor reading that the EVAP is freezing up and the PCM shuts the compressor off. Make sure you are reading the EVAP temp sensor and not the AAT sensor. If the EVAP sensor is reading -40, the AC compressor will not turn on at all.Also, double check the wiring connectors to the 2 sensors you checked. Below are the connector views and make sure you are getting the proper readings.
Customer: replied 1 year ago.
I am checking the second connector, in front or the condenser/radiator
Expert:  A. Penland replied 1 year ago.
What are you using to read the -40 on the AAT? Scan tool?
Customer: replied 1 year ago.
On the screen on the dashboard... Ext temp
Expert:  A. Penland replied 1 year ago.
Ok. The instrument cluster gets the outside temperature reading from the PCM (Engine Computer). The PCM controls the AC system, not the instrument cluster. Since there are no trouble codes in the PCM, I do not think the AAT is the problem.
Customer: replied 1 year ago.
So what sensor tells the PCM what the outside temp is for the dashboard? I read on Fords website that the AAT sensor is used by the PCM to determine whether the compressor runs for defrost issues based on the outside temp
Expert:  A. Penland replied 1 year ago.
Yes it does. The AAT monitors the outside air and the Evap temp sensor tells the PCM what the evaporator temperature is and if it is freezing up. Have you had all the modules in the vehicle checked for trouble codes?
Customer: replied 1 year ago.
No, My reader will only do the PCM I guess
Expert:  A. Penland replied 1 year ago.
Below is the pin point test we have to follow.And if the PCM had an issue with the AAT, it would set a trouble code.
Customer: replied 1 year ago.
So I am not getting passed step1... "The PCM does not detect an ambient air temperature below -1°C (30.2°F)."
Expert:  A. Penland replied 1 year ago.
Is your reader monitoring the AAT or are you basing the answer off the instrument cluster display?
Customer: replied 1 year ago.
Off the cluster display... Its a cheapo reader
Expert:  A. Penland replied 1 year ago.
But the instrument cluster may not be getting the proper information from the instrument cluster or there is a problem with the cluster. You need to see if the PCM is reading the sensor properly by monitoring the PCM, not the cluster. The wiring goes from the sensor, to the PCM and then the PCM sends the reading to the cluster.