Air Conditioning Maintenance – Under the Hood (Part 2)

Let’s look under the hood and see if there are any signs of impending failure. Any A/C hose with bulges or cracking can cause a major blowout and quite a mess. If you see oily areas on the A/C hoses, you’ve found a leak. For that matter, any A/C component with an oily film has a refrigerant leak. As refrigerant leaks out, system lubricating oil is pushed out first, which eventually leads to compressor failure. Low refrigerant can cause evaporator icing on 66 – early 77 Corvettes. These Corvettes keep the compressor running constantly using a POA valve to bypass refrigerant instead of cycling the compressor. You’ll know the evaporator has iced up when you started out with good airflow and midway through your trip the airflow from the vents is nonexistent.

Another sign of low refrigerant is frequent compressor clutch cycling on late 77-93 Corvettes.

We used to be able to check the sight glass in the drier on early Corvettes for refrigerant level when R-12 was used. Now that R-134a is used in almost all applications it requires less refrigerant and consequently bubbles will show in the sight glass. When the outside air temperature is above 80 degrees, the A/C compressor clutch will rarely cycle on and off until you’re at highway speed. If the compressor is cycling frequently, be sure to add a few ounces of refrigerant oil along with the refrigerant to replace the lost lubricant if you decide to just top off the system.

Take a look at the A/C compressor belt for any cracking or glazing and replace as necessary. Although not a part of the A/C system directly, make sure the fan clutch is engaging when the A/C is on and you’re at idle for max cooling.

As we wrap up our A/C checklist, we’ll list a few common areas of concern and their fixes on early and late Corvettes:

63-67 Corvettes have a compressor switch on the temperature blend door behind the glove box; frequently we find the switch gets dirty contacts and the compressor won’t come on. Usually this happens after sitting over the winter. Moving the cable back and forth (moving the temp knob hot to cold) to operate the switch on and off typically knocks the corrosion off.

A very common problem with 68-82 Corvettes is vacuum hose deterioration causing air flow distribution problems. You’ll find that the three vacuum hoses are crumbling to dust at the firewall behind the distributor. When this occurs, the air distribution doors won’t move and you’re stuck in defrost/heat mode all the time. We have A/C vacuum hose kits to replace the complete hose assembly with routing instructions to bring the vacuum system operation back to life.

63-77E A-6 and R4 compressors are prone to front seal leakage and over time the leaking oil slinging onto the underside of the hood will make repainting the top side impossible. The oil leaches into the hood and propagates to the surface making the paint bubble.

77L to 87 Corvettes use R4 compressors that have vibration issues which are exacerbated when mounting brackets or braces are loose. R4 compressors also have a very small lubricant reservoir so lubricant loss is quick death to the compressor. Be sure to add lube anytime refrigerant is added.

88-96 Nippondenso compressors are very reliable but the compressor clutch fails in the 80,000 to 120,000 mile range. The good thing is the clutch can be replaced and the compressor just keeps going.

90-93 Corvette automatic air programmers get brain fade at times, causing hot air when you don’t want it and other behavior issues. Simply remove the courtesy and A/C fuse for ten seconds to allow it to reboot and in most cases the system smarts will return.

86-96 automatic air cars can have an issue with the blower running all the time even with the key out of the ignition. This is caused when the power module on the top of the evaporator case fails. You can remove the large connector on the case to shut down the blower to prevent a dead battery until it can be replaced.

97-04 Corvette A/C systems have been pretty reliable. We find some compressors have a tendency to leak and there are some issues with mode actuation motors that cause hot air when you want cold air.

Most importantly, the thing to watch out for is battery acid damage. With the battery directly above the computer and major harnesses, vacuum hose damage can result, not to mention catastrophic wiring damage. Like the early cars, no vacuum and the distribution system doesn’t work properly. If you find that the air won’t switch from A/C to defrost, check under the battery for acid damage.

Close the hood and enjoy the cool breeze while you’re cruising the hot summer asphalt.

This article was written by Chris Petris for Corvette Central.