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HDGENE, Ford Senior Master/Diesel/Trans
Category: Ford
Satisfied Customers: 4782
Experience:  25 years Auto experience, Ford ,GM, Chrysler, Asian & European
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A/C compressor will not engage, no grond signal from

Customer Question

A/C compressor will not engage, no grond signal from computer
JA: Have you checked the Freon level?
Customer: charged
JA: What is the model/year of your Ford?
Customer: 06 Fusion 4 cyl 5 spd
JA: Are you hoping to fix this yourself? What have you tried so far?
Customer: I can ground the compressor ground to a ground source and it will engage
JA: Anything else you think the mechanic should know?
Customer: ?
JA: What confuses you?
Customer: My Snap on Scan tool shows that the PCM is not sending the Ground signal to the compressor, I jumped in a new temp control sensor and that did not cure the problem
Submitted: 2 months ago.
Category: Ford
Expert:  Cary York replied 2 months ago.

Hi, I’m Cary and I’ll be helping you today.
Please understand that I can't smell, hear, or touch the vehicle, so patience is appreciated. Before leaving the site make sure and leave me a rating. You can still reply to me as many times as needed, even after the rating..

Does it have auto or manual A/C control?

Customer: replied 2 months ago.
Will having the computer reprogramed fix it?
Expert:  Cary York replied 2 months ago.

No. Let me look at a wiring diagram. I'll be right back.

Expert:  Cary York replied 2 months ago.

Here is a diagram of the compressor circuit. Are you referring to the ground that the PCM sends to the relay?

Expert:  Cary York replied 2 months ago.


Customer: replied 2 months ago.
Expert:  Cary York replied 2 months ago.

So when you ground compressor relay the compressor engages?

Customer: replied 2 months ago.
Well I did not try to ground the relay, I just ran a ground to the compressor terminal ground
Customer: replied 2 months ago.
By passing the PCM and the relay
Customer: replied 2 months ago.
I purchased a used probe several years ago and that is what someone else had done. And just installed a switch to turn the compressor on
Customer: replied 2 months ago.
In other words they switched the ground to make it work
Expert:  Cary York replied 2 months ago.

To help better serve you and give you accurate repair help we need to talk.

Customer: replied 2 months ago.
would be alright but they already got me for 28.00 so that's kinda un fair
Customer: replied 2 months ago.
Well..? I did not get an answer to my question.
Expert:  HDGENE replied 2 months ago.

Hello, you jumped in a new evaporator temperature sensor? No codes? How did you jump the sensor, with a fixed resistor?

Customer: replied 2 months ago.
I removed the #3 & #4 pins from the blue connector behind the glove box door and connected in a new sensor and plugged the connector back in. All I bypassed was where the sensor was located.
I am getting a code that tells me the ground is NOT being sent by the computer to the compressor, for what ever reason. I have replaced the pressure switch, temp sensor, and relays in the fuse box under the hood, no change.
The car has been wrecked and repaired and the AC worked fine for about a week then just quit working. No other problems.
Expert:  HDGENE replied 2 months ago.

Ok does your scan tool show any codes for the temp sensor? Can the scan tool verify the temperature sensor reading isnt below 32 degrees? Does it show the ac switch demand on?

Expert:  HDGENE replied 2 months ago.

Do you need more help with this concern?

Customer: replied 2 months ago.
The scan shows a reading of -40 on the existing sensor, I was not able to get a scantool to check the other sensor I installed and the dealer would not scan the vehicle with make shift installation to see if anything changed-so tomorrow I will install a new sensor from NAPA to see what happens. But since no one wants to scan the car with the make shift sensor installed, it will just be hit and miss. Since I already know I can bring in the compressor by grounding it at the connector, and have driven another vehicle over a 100k with this switched ground installed I am not afraid to do it. I am not going to waste my time removing and reinstalling the Dash without proof that the sensor is good. It makes no sense to do so.
Expert:  HDGENE replied 2 months ago.

Ok, The temp sensor is a thermistor. So it change its resistance value based on temperature. In order to know for sure f the way the new sensor is installed correctly is to check the temp sensor input value.

Expert:  HDGENE replied 2 months ago.

Do you need more help with this concern?