Understand and Repair Climate Control

Few things are more frustrating than interior airflow in places it isn't needed. For example, it's a humid morning and you need a clear windshield. You slide the climate control to DEF and wait for the air on your windshield that never arrives. Perhaps your feet are cold and could use a warm-up. Sliding the control to HEAT nets you nothing but hot air--from the air-conditioning outlets. It's 95 degrees outside, with relative humidity of 100 percent, so you nudge the control knob to MAX. But what you get is MIN. Can you see our point about climate-control malfunction?

Climate-control systems quit working properly for a variety of reasons. Vacuum hoses, switches, and servo-motors develop leaks. Air-conditioning compressor switches burn out. Thermostatic switches fail. Heater control valves stick. And blowers simply stop working. We're going to address climate-control- system basics for '67-'78 Mustangs with factory air conditioning. We'll show you how simple it is, and how to get it working when it won't.

Vintage Mustang climate-control systems are a wonder of ingenuity. The standard heater uses cables for specific functions, but the climate-control system utilizes the engine's intake-manifold vacuum instead. For example, when you move the climate-control selector to HEAT, vacuum is channeled through the vacuum switch to the right combination of servo-motors, which move doors inside the system to direct hot air to your feet. Slide the control to MAX or FRESH air conditioning, and you get vacuum-operated door movement, and also the closing of switches that engage the air-conditioning compressor clutch.

Things quit working properly when vacuum hoses are misconnected. Next thing you know, you have cold air on your feet or hot air in your face. Particularly frustrating is the absence of defrosters on a frosty morning.

This article isn't about the refrigeration side of your Mustang's climate-control system. Rather, it's about handling the hot and cool air inside your passenger cabin.

Weak Link Solution
In 1967-1968, the Mustang's A/C-DEFROSTER door lever was made of steel, which made it strong and reliable. In 1969-1970, Ford replaced the steel with plastic, which breaks with great regularity. Until recently, no one reproduced this part, forcing enthusiasts to roam salvage yards and used-parts vendors in search of replacements. Southern California's Mustangs Etc. saw the need to reproduce this elusive plastic lever, which helps the vacuum servo move the A/C-DEFROSTER door on '69-'70 Mustangs (and Cougars). It's now available as a complete repair kit, including the lever and retainers. We're going to show you how to install it.