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Pete, Technician
Category: Mercury
Satisfied Customers: 27535
Experience:  Over 17 years diagnosing and repairing automobiles various makes and models with some training and certifications.
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Ac will not come on I can jumper relay pins then will work

Customer Question

ac will not come on I can jumper relay pins then will work if car sits it will not restart till I jumper relay pin from hot lead to compressor lead
Submitted: 1 year ago.
Category: Mercury
Expert:  Pete replied 1 year ago.

Hi my name is ***** ***** I will be happy to assist with this today.In some cases I may need more info to assist better.I apologize for any delay.

Can you tell me the year and model of this vehicle as well as engine size?

Does your model have the manual heat and ac controls or the AUTO settings on the controls?

Has anything been checked,tested or replaced to try and locate or correct this issue?

Have you had the fault codes checked using a compatible scan tool for your model to see if any codes are set in any of the vehicles computers?

Let me know so we can continue,thanks Pete.

Customer: replied 1 year ago.
2007 Milan code po538 which I replaced acet sensor then code was gone this is a manual system I cleared code then it still would not come on if you check the relay it has battery power then when you turn key on it puts power to the relay pin that should put power to the compressor but the pin with the compressor wire will only work when I put power to it then will work fine till I shut off car for about 10 min it will not come back on till I jump again
Expert:  Pete replied 1 year ago.

Just to be sure here have you re checked fault codes to see if this same code came back after you replaced the sensor and cleared the codes or if any new codes had set at all?

Customer: replied 1 year ago.
no codes just not starting air
Expert:  Pete replied 1 year ago.

O.k.,the relay coil receives a ground from the PCM (engine and transmission computer).It sounds like your not getting this ground at all.Usually this only occurs if the PCM still detects a fault and a code is set or if there is an internal fault in the PCM itself.Below is the diagram for your system here.

Check and see if there is a break in this wire leading from the PCM to the relay including at the battery junction box fuse panel where the relay is seated as this can be a common fault in some cases.If the wire is o.k. and you have no codes set and your freon is at the correct fill this can indicate the PCM itself is at fault here.

If more help is needed, use the reply tab to continue our conversation. If no further assistance is needed, kindly rate my service.You can rate at any time and we can continue to work on your question as this will not close out your question.Keep in mind in some cases it can be difficult to fully diagnose or help repair your vehicle without seeing it and I work on delivering the best possible answer from what I see to work with.

Thanks Pete

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