A/C Repair

The right tool for the job. The guys at Classic Auto Air use a specialized wrench to undo the valves. This shot is an example. You should have your gauges hooked up before you do this. The tool prevents the flats on the valve from being damaged. If you've used the wrong tool and chewed up the threads on the high-pressure hose, Classic Auto Air has the correct valves to replace them. Just be sure that you evacuate the system before replacement.

By law, if your system has been converted to run 134A, a sticker should be on the compressor or displayed prominently in the engine bay. Classic Auto Air uses this machine to detect the type of refrigerant in the system. Ours was pure R12. They have seen cars with grab bags of refrigerants. One car had Propane, R12, and 134. This situation could be bad news for a shop during recovery since any of those three will contaminate a tank of refrigerant. With R12 running at $29 for a 12-ounce can, the results could be hazardous.

First Doug checks for a good connection at the fuse block. A test light is essential for this. You might be surprised by how many cars are OK aside from a blown fuse. Doug recommends checking the service manual for the correct size fuse. The '71-'73 Mustang uses a 30 amp fuse. Our fuse link was fine, so we moved on.

From the underdash fuse panel, we turned the ignition to the on position, activated the A/C, and moved to the compressor-switch link. Trace the black wire from the compressor back to the link, and separate. Use the test light to see if there is power. Our car showed none.

Doug also checked the link at the firewall. On the '71-'73 Mustangs, the male and female plugs are both green. The plug had been rat food at one point but showed no frayed wires. The female side showed no power.

Doug then removed the glovebox inside the Mach's cab to check the thermostat switch on top of the case. You can see two wires plugged into a silver block; the block is the A/C thermostat or de-icing switch--no power here either. At this point, both Doug and Mike Fleshman suspected the clutch switch on the control panel.

After partially removing the panel, the clutch engaged. Still, Doug felt we needed to replace the switch, since it was an intermittent problem. Doug suggested bending the female clips to tighten the fit and improve the connection. We did this, but the operation was still intermittent.

We dumped the old switch for a new one from Classic Auto Air. This solved one problem but led us to the other checks you can do at home.

We'd not yet checked for a condenser with separated coils. Since the fins cool the system, if they are separated, they can affect the efficiency of the A/C. One row won't hurt you so bad, but multiple rows will.

Al also told us that the fittings could show tell-tale signs of problems. Because there is oil in the pressurized system and the pressure can push oil out around damaged O-rings or fittings, there may be a dark, sooty film on the fitting. This film is composed of debris from the road and engine bay. This leak may be slow or quick, but eventually it will rob you of freon.

The valves can also leak. Again, they'll have oil on them, but the debris may be less if the caps are still on the system. These are available from Classic Auto Air.

Check the hoses for pinching like we see here on our test car. The high-pressure hose has been pinched and crushed by an aftermarket hose. Though this one doesn't seem to leak, hoses like this should be replaced. Check the hoses for damage at the connections and along the passenger side as well as over the exhaust manifolds. Classic Auto Air has new hoses that look and feel like the originals.

One thing missing from this system is a sight glass, an effective tool for checking an A/C system with R12 for correct function. On correct systems, you should be able to see the refrigerant and air bubbles moving past the sight glass.

Al says hoses with the longitudinal crimps don't keep the freon in place. He was even able to spin the hose on the hard line--another place for a leak.

Note the incorrect mounting and style of the hoses as well as the trick Motorcraft catch can for radiator fluid. According to Al, oil and debris on the fins is another indication of a bad condenser. This is a problem, particularly around the fitting nuts.