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rashawn, ASE Certified Technician
Category: Ford
Satisfied Customers: 393
Experience:  master tech 20 years experience
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2001 mustang: electrical..control module (ECM)..already replaced..hose

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I have a 2001 mustang (4.6) that has a/c problems. I have a mechanic that has diagnosed the problem as being electrical and is requiring the control module (ECM) to be replaced. They already replaced the suction line, acumulator, and a return hose along with evacuating and recharging the system (initial diagnosis). Everything appears to be functional except the compressor won't stay engaged.
Is this a realistic diagnosis, or could it be something else?
Can someone tell me approximately how much this part and service should cost?

How long does the compressor operate?

how long does it stay disengaged

are you sure the system is full

do you have any check engine light or codes in the system

Customer: replied 8 years ago.

The compressor run time varies. When we got it out of the shop it cycled fine for approx 2 hrs while running errands and then would not come back on at all.

I'm not sure about being disengaged. It's intermittent.

I can only go on what the mechanic told me. He said the system was full.

No check engine lights or codes. The battery light does come on occasionaly, but no one can tell me why, because evrything allways checks out ok.

  1. This is a realistic diagnosis depending on how competent. It would be wise if ha hasnt already done so to test the. voltages at different points when the a/c is not working. Also keep an eye on the pressures.
  2. If the pressure on the high side gets to high the system will shut off.
  3. If the low pressure switch is bad it will shut off from time to time
  4. If the onboard computer senses an issue it will shut it off.
  5. The battery light on is an indication yhere is a problem in your alterngator if the onboard computer system senses a low voltage issue it can very well turn the a/c off.
  6. The a/c relay getting hot and turning off system

I would focus more on the charging system at this point. Ask mechanic with A/c on is the pcm getting its signal from the low pressure switch. and if so is the ground signal leaving the pcm to activate relay. this might get him thinking . This vehicle is a later model. Kinda hard to believ pcm problems. these newer pcms do not go out often.

rashawn and 6 other Ford Specialists are ready to help you
Happy your problem is resolved hopefully it wasnt that difficult