Compressor-Clutch Sensors Save Air Conditioning Failures

By Larry Stewart, Executive Editor | September 28, 2010

Tom Hogan, with Silver State Materials
Tom Hogan, with Silver State Materials, says the A/C compressors in 40 of its mixer trucks equipped with the ACX-10 (in his right hand) cycle about half the normal rate. Silver State stands to save about $13,000 per year in compressor failures.

The ACX-10 Air Conditioning Life Extender monitors air-conditioning (A/C) refrigerant pressure and clutch voltage and prevents the compressor from operating in self-destructive conditions.

Both high and low refrigerant pressure can force the compressor clutch to cycle on and off rapidly, causing premature wear of the compressor, compressor clutch and hoses. When refrigerant pressure swings high or low (if the system is overheating or low on refrigerant, for example), the ACX-10 prevents rapid clutch cycling by fixing each on/off cycle at 15 seconds. It can cut cycle frequency by as much as 80 percent.

Silver State Materials, a Nevada ready-mix producer that has installed ACX-10 on half of its 82 Peterbilt mixer trucks, figures an A/C compressor failure costs $500 to $600, including parts and labor. The firm's shop replaced 23 compressors last year. Tom Hogan, Silver State's assistant maintenance manager, says compressor clutches in trucks without the module seem to be cycling twice as much as those without ACX-10.

Running for long periods at extreme high or low refrigerant pressure can cause expensive A/C breakdowns. A compressor laboring under very low pressure can lose lubrication and seize. Chronic high pressure can rupture hoses and fittings. When the ACX-10 detects persistent, potentially damaging refrigerant pressures, it disengages the clutch until system pressure returns to the safe operating range.

The ACX-10 also detects extreme voltage. Over-voltage pushes excessive current through the electric clutch coil. The coil overheats, shortening clutch life. Under-voltage can cause the clutch to slip, and the friction surfaces will eventually burn up. When the ACX-10 detects improper voltage, it disengages the A/C clutch until the voltage returns to normal.

The module also protects the starter motor and batteries. If the A/C is on during a vehicle's ignition cycle, the starter motor has to crank the compressor as well as the engine. The ACX-10 extends starter motor and battery life by delaying A/C clutches engagement for 15 seconds after ignition.

An important feature of the ACX-10 is its ability to directly sense pressure on the low-pressure side of the compressor. This allows it to detect a low refrigerant level before it falls to the point of causing compressor damage.

Index Sensors has been offering OEM and aftermarket control systems since 1995, and Index devices have been installed in more than 500,000 trucks, buses and off-road machines. Caterpillar recently began offering the off-road version of the ACX-10, designated CM-810, as standard equipment on mining trucks, large dozers and scrapers.

The ACX-10 is available in an aftermarket installation package through dealers and parts distributors. The units cost about $150 each, and one can be retrofit to most vehicles in about 30 minutes.