A/C Repair

Al says that low oil is a pervasive problem inside the compressor. Most compressors come into the shop with three ounces of oil in the crankcase; they should have 11. Do not try to check the oil with the system pressurized. Have the shop that does the final evacuation of the system check the oil before they do the deed.

This one is more about better functioning A/C, but make sure the fan shroud is present and functioning. Also check the fan clutch (if so equipped) for proper operation, as this will affect cooling efficiency. The '71-'73 Mustang used a flex fan, so this isn't an issue for us. To check the fan clutch, run the engine to operating temperature and shut off the engine. If the fan is loose and continues to spin, it needs replacing.

Check the heater hoses and heater valve for correct function. Sometimes the valve inside the heater hose can be damaged, allowing too much coolant (and thereby heat) to enter the heater core, cutting cooling efficiency.

While in the region, look at the pulleys. Al recommends that you take the belts off and turn each A/C pulley. If the pulley drags or feels like it has sand in it, it should be replaced.

Check all the blend doors for correct function, and consult the service manual for the function of the doors.

Our Mach 1's vacuum motor on the restrictor door was bound up and causing problems. Doug freed the malfunctioning door, causing it to function correctly again.

The Mustangs' restrictor doors get rusty due to cowl-vent leaks and bad heater cores. The only real fix is to disassemble the A/C box, bead-blast the door and rod, and paint the assembly.

Al recommends checking the vacuum reservoir for its ability to hold a vacuum (one of its functions). This is especially important if you have a Hi-Lift cam with a low vacuum reading. The can keeps a vacuum when operating properly. You can check this by moving the selector switch after the car has sat with the engine off for a half hour or so. You should be able to hear a hiss as the A/C selector switch is moved back and forth. If you don't, consider replacing the can.

Here are the corrected A/C lines and a new bracket from Classic Auto Air. Doug put new O-rings on all the fittings, set all the hoses in place, and put tension on them once they were in the correct position.

After we installed the correct hoses, Doug evacuated the system and put the new R12 freon into the car. Note the fluctuation on the gauge above. This is a sign of a bad set of reed valves. Though not serious enough to cause major problems, the compressor could stand a rebuild. If the compressor were new, the reading would be solid.

Mike leak-tested the system and found it to be sound. Sometimes the test can net a bad evaporator, especially if it is an original aluminum one. This would require the system to be drained and the evaporator core replaced. Fortunately, ours was in good condition, and we got 40 degrees at the vent from our new hoses and original system.

Late in the day, we did the final test. Dana "The Cheater" looked under the car to make sure the system was draining. It was, and all was right with the A/C world.