A/C System Performance

Ways to reduce costs, unexpected downtime for A/C related repairs

Burrow says there are three things to remember about reading voltage:

Re-create the full demand for voltage. "With the engine and air conditioner running, turn on lights, wipers, radios - anything that draws power. Then take a reading. Ideally, we want 13.5 volts but not less than 11.5 volts at the clutch coil."

Look inside the cab or sleeper for an aftermarket power inverter with 110-volt AC outlets, evidence that the driver is drawing even more power from the vehicle's electrical system.

Many clutches are grounded through the compressor casing, as indicated by a single wire on the power side of the clutch. A ground can be picked up on a bolt or bracket, but sometimes that bolt or bracket is the source of the bad ground due to corrosion or even resistance that comes from paint. With a case-grounded clutch, measure the ground at the compressor body.

"The clutch is the heart of the system and the number one warranty cost item in the A/C system," points out Burrow. "Perform a simple visual inspection every three months, looking for discoloration on the face of the clutch hub - a sign of heat; oil or dirt around the shaft seal - which signals a leak; proper alignment of the clutch pulley and crankshaft drive pulley; and glazing or cracking on the belts.


In this case, the dot is the moisture indicator on the receiver-dryer's sight glass.

The receiver-dryer removes moisture from the system and filters refrigerant. Whenever the engine oil is changed or a vehicle is in for scheduled maintenance, Burrow recommends checking the sight glass on the moisture indicator. A blue dot means the refrigerant is dry; pink, white or grey indicates acid or moisture in the system.

In general, a dryer should be replaced once a year or every time the A/C system is opened. Check with the vehicle's manufacturer for specific recommendations. Mark the installed date on the new dryer so it's easy to see.


"The mobile A/C market has some of the best all-makes parts options in the heavy-duty aftermarket to help reduce inventory and parts costs," he says. Examples include the Sanden FLX7 family of compressors, which enable "replacement of the majority of Sanden's OE compressors with just 15 models and five head adapters, and Aeroquip's E-Z Clip system - a fast, effective way to create hose fittings for any make of vehicle.

"Talk to your A/C parts suppliers about how they can help you service a broader range of vehicles with all-makes parts. Buy from a trusted source so you know you're getting a part that's an exact match for the fit and performance of the original."


"Your primary diagnostic tools are with you all the time: your hands," says Burrow. "Obviously, touch and feel aren't going to replace your service equipment. But they're a good first step in the troubleshooting process."

For example, a properly functioning receiver-dryer should be warm to the touch. If it's cold when the system is running, the dryer may have moisture or a restriction inside. It's normal for frosting to occur during the recovery process.

Grab a hose and palpate it, he suggests. Hoses tend to deteriorate from the inside out, shedding debris into the refrigerant or coolant. A spongy hose is a sign that it's weak and should be replaced. Feel the tension on the hose connections and make any necessary adjustments.


"Old rules of thumb say you should add so many ounces of oil when you replace a condenser, so many ounces when you replace an evaporator, etc.," says Red Dot's Burrow. "In fact, the only way to determine how much oil to put back into the system is to drain the oil from the old component, measure the amount you removed and replenish the system with the same amount of oil when you install the new component."

The compressor demands even more care when it comes to lubricants. Most replacement compressors come pre-charged with 5 to 10 ounces of oil depending on the make and model, he says. The type and amount should be clearly marked on the compressor's label. Don't rely on product literature or catalogs. The pre-charge means there should be no need to add oil when you install a new compressor.

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