The Pantera Place
"Your de Tomaso Connection"
Air Conditioning System Pressure Switch
By Mike Dailey
One of the things missing in the Pantera air conditioning system is a high/low pressure switch. In most modern A/C systems a pressure switch is used to shut down the system if high or low pressure is detected. This can happen If the system malfunctions. Pressure will build up and can blow a hose off venting all of your expensive refrigerant, e.g. the condenser fan fails. Low pressure happens when the refrigerant is low. Ford issued a number of TSB that addressed the high pressure problem including having the condenser fan run anytime that the heater blower was on and on later cars adding more relays and a improved A/C control.
My Pantera is a 1971 model so it has one relay that controls the compressor clutch and condenser fan. I installed the pressure switch so that if high pressure (about 300lbs) or low pressure (about 10 to 15lb) condition exist the compressor and condenser fan will shut down until normal pressure is reached. The switch can be installed on later cars so that only the compressor is shut down.
The above drawing shows where the switch is installed in the AC system. The switch is located on the top of the receiver dryer and can only be installed with the refrigerant removed. Not all receiver dryers have a fitting to mount the switch so make sure you have the correct receiver dryer. My switch and new receiver dryer was installed at part of my system up grade.
I used Radio Shack 2 connecter wire (#278-567) 18AWG to wire the system. This wire has a red and black lead and I used NAPA black plastic wire loom to cover and shield the wires (#737299). The pressure switch projects above the receiver dryer and I reformed the switch connecter lugs to clear the trunk liner.
View of the reformed switch connecter lugs.
Heat shrink tubing was use to cover the lower part of the lugs.
90 degree connectors were used.
View of the wire loom being installed over the wire.
The wire was routed along with the AC hoses and over the top of the electrical panel and through an existing hole in the firewall.
The wire enters the car behind the passenger seat, then goes to the back of the console, then along the top inside (passenger side) of the console and then out the front of the console. Make sure it is away from the shift linkage. I don't know why I took the shift gate off, it didn't help any. Obviously, the wire must be inside the loom before it is routed through the console.
This view shows the back side of the AC control (the round knob on the right side of the console) with the white/black wire removed from the switch.
The two wires from the pressure switch have a male connecter on one wire and a female connecter crimped on the other wire.
The male connecter is connected to the white/black wire and the female connecter is connected to the terminal on the switch.
View of the completed installation. The system was tested to make sure that the compressor clutch and condenser fan worked.
This mod can also be done to later cars that have the AC control with three wires. On these switches the pressure switch should be in series with the wire that goes to the compressor relay. One of the Pantera wiring diagrams that I looked at for the later cars shows that the white/black wire controls the compressor. This might vary by car serial number so make sure you use the correct wire to control the compressor.