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.

Read More

Air Conditioning Maintenance – Air Flow (Part 1)

Like they say, “Baby it’s Hot Outside.” Summer is here and it seems like each year it gets tougher and tougher to stay cool. Here are a few basic things to check to avoid major meltdowns on those summer cruises.

We discussed the cooling system earlier this year and that’s the number one concern: hot engines make hot interiors. If you’ve been following our Tech tip series, you’ve checked out the cooling system and prepped it for spring so you’re ready to move on to the A/C system.

To begin with, the A/C system needs a debris-free condenser in front of the radiator to allow ultimate interior cooling. Any debris blocking airflow will raise the interior temperature. Check the condenser fins for debris and if necessary use your garden hose to flush away the buildup. Stubborn debris may require air pressure to dislodge it, so we made an extended air pressure nozzle, allowing us to blow the debris out the opposite direction that the air flows through the condenser. I know what you’re thinking. If the condenser airflow is limited, engine temperatures would be elevated but air can flow around the condenser and keep the engine temp in range while causing poor A/C performance.

While we’re discussing air flow, we need to check the air intake part of the system. When normal A/C is selected, outside air is continually circulated through the cockpit with the air coming in from the cowl area below the windshield. 63-82 cars have minimal screening to prevent leaves and debris from getting into the intake air stream. The build up eventually limits airflow into the cockpit. The real concern is as the debris builds up it blows directly onto the evaporator and it doesn’t matter if you have the system on maximum or normal, A/C air flow can be severely restricted.

We have a simple to install cowl vent air filter (73-82) to keep the infiltration of harmful debris to a minimum. If you don’t have the filter and feel that the airflow isn’t what it used to be, especially if you have some tell-tale leaves lying in the passenger side cowl area, clean up may be required. To start with, the debris drops to the bottom of the cowl and builds up, eventually allowing the debris to be pulled into the blower motor. You can feel for debris when the A/C is on maximum by checking in the cowl vent door area at the passenger side kick panel. You may want to wear gloves as you never know what you may find in the bottom of the cowl area. Most likely you’ll find a handful of leaves that a shop vac will pull out quickly.

Here’s the rub though. If the debris is left in place long enough, it blows onto the evaporator severely limiting airflow into the cockpit. In the worst case the evaporator case has to come apart for cleaning. In most cases the blower motor can be removed and the shop vac hose snaked into the evaporator area. We use a piece of small diameter hose and connect it to the vac hose to allow the hose to get into the evaporator area.

We have a cockpit air filter (for 84-96) which does a great job of keeping dirt and dust out of the A/C ductwork and off of your upholstery. Leaves aren’t as big a concern on the later cars as long as the cowl screens are intact.

97-04 Corvettes can ingest leaves also and our cowl filter will keep fresh air flowing for maximum A/C performance and now the latest C6 Corvettes have a cabin filter to keep odor and debris from the cockpit.

If airflow is still a concern, the foam seals have most likely deteriorated and dried up affecting airflow volume. The leaky internal ductwork seals keep the cold air behind the dash. Improperly operating air distribution doors prevent air from flowing where you need it most. We have the necessary parts to reseal and completely restore your early Corvettes A/C inner ductwork and distribution system.

The parts costs are reasonable. The labor is extensive and requires skilled hands to make the system new again. We can take some of the trepidation away with our service and assembly manuals though.

Once you’ve got debris-free air flowing into the cockpit you may want to check the condensate drain at the bottom of the evaporator for plugging. Water should flow constantly when the A/C is on. When the drain stops up, the floor gets wet. The drain is close to firewall at the bottom of the plastic evaporator case on early cars (63-96). Later Vettes have the drain coming out the firewall below the battery area. Don’t use any sharp tools to dislodge any drain debris. Gently move a small screwdriver around until the debris falls out.

This article was written by Chris Petris for Corvette Central.

Read More