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Dr. Hamman
Dr. Hamman, Technician
Category: Classic Car
Satisfied Customers: 6286
Experience:  I have 30 years experience repairing, restoring, and customizing cars, and pickup trucks.
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1973 Ford LTD Where is the pressure switch that kicks the

Customer Question

1973 Ford LTD Where is the pressure switch that kicks the a.c. Compressor on? I can jumper the compressor clutch & get cold air. But the system isn't sending the signal on its own.
Submitted: 1 year ago.
Category: Classic Car
Expert:  Pete replied 1 year ago.

Hi my name is ***** ***** I will be happy to assist with this today.I apologize for any delay.My info is limited on this here but I saw no one else had posted and wanted to see if I could help in any way on this.

Inspect for any broken wiring leading to the compressor clutch.I have seen broken,corroded and damaged wiring cause this type of fault here and had to repair it.In some cases the wiring had to be replaced.If this has already been checked and found to be o.k. let me know.

Let me know if you need anything else and feel free to rate my help here as this is how I receive credit for my time.Thanks Pete

Customer: replied 1 year ago.
Hi Pete. The vehicle has 17,000 miles on the clock. It's been garaged its entire life. There is no corrosion. I need to know the location of the pressure switch in the a.c. System. I feel like it's most likely stuck.
Customer: replied 1 year ago.
I'm not sure what to do here. I don't want to give a poor rating, but my question wasn't answered.
Expert:  Pete replied 1 year ago.

I apologize for the delay as I was out of town.

Unfortunately I do not show the exact location of this switch here but someone else here may have this info.

I will open your question up for others here to see if someone else can assist further on this as there may be others here that may have more info on what to check or do with this issue.I hope you can get this resolved with ease.No need to reply to my last post here unless it is a last resort as it will keep your question locked to me and others will not be able to view it.If you feel you want to continue to work with me on this feel free to reply at any time but keep in mind in some cases it can be difficult to fully diagnose or help repair this without seeing your vehicle.

Thanks Pete

Expert:  david craig replied 1 year ago.

Hi Im David, I will try to help but these older LTD's are extrememly difficult to find a lot of information for. take a look at this pic. i believe the pressure switch is in the red circle on the right side of the pic.

Expert:  Dr. Hamman replied 1 year ago.

I am an electrical specialist, and I saw your question hadn't been answered yet. These Old LTD's didn't have a pressure switch that cycled the AC compressor. It is a pretty crude setup, that controls the freon flow with an expansion valve. That was strictly mechanical to increase/decrease the freon flow to control the evaporator temperature. Some early LTD's had an ambient temperature limit switch installed on them. If the expansion valve couldn't control the freon flow, the ambient temperature limit switch would shut the compressor off to try to prevent the evaporator from freezing up. The ambient temperature limit switch would be located on the air box under the dash, or on the evaporator housing under the hood, near the expansion valve. Normally light green W purple wire would come out of the dash AC switch to the ambient temperature limit switch, and a black W yellow wire would go from the ambient temperature limit switch to the AC compressor. Use a voltmeter to see if power is getting to the AC clutch with the AC on, if it has power check the clutch coil ground, and then the resistance of the AC clutch coil if the ground is good, and power is present. If you have any more questions feel free to ask.

Customer: replied 1 year ago.
Thank you! I'll check that out when I have time. I appreciate the info!
Expert:  Dr. Hamman replied 1 year ago.

I am happy to help, good luck with it and thanks for using Just Answer.