Maintenance managers can lose their `cool' when air-conditioning failures rise. Here's a way to avoid that.
Forget winterizing. It's time now to think about springizing.
For many maintenance managers, March and April can seem like the hottest months of the year. Why? Simply because, as the temperature rises in early spring, so does air-conditioning use, and many fleets notice a sharp rise in A/C system failures -- as much as 30%, according to engineers at Index Sensors & Controls.
The solution offered by this Redmond, Wash.-based manufacturer of A/C control systems is its APAds air-conditioning protection and diagnostic system, which was displayed at the 1996 SAE Truck & Bus Meeting & Exposition and which was evaluated in a 1-yr./9,000,000-mi. fleet test, the results of which were released during the meeting.
A panelist at SAE's "Tomorrow's Truck" session pointed to APAds as one of the improvements made in his company's heavy trucks in response to fleet maintenance managers' call for better vehicle performance and maintainability.
"Air conditioning is an area where reliability and repairability are of great concern to the fleets," said Paul Middelhoven, chief engineer at Kenworth Trucks. "We use a blend-air system that allows the driver an unlimited number of air-flow settings, and an air-conditioning protection and diagnostic system is standard. This system [clearly identifiable in a slide as APAds -- Ed.] shuts the air conditioning down in the event of a failure, thereby preventing a major repair job. It also lets the driver or mechanic know what type of failure caused the shutdown, simplifying troubleshooting."
The APAds system is designed to improve A/C reliability by actively monitoring system conditions, controlling the refrigerant compressor, regulating fan-drive engagements initiated by the A/C, and communicating diagnostic LED blink codes to service technicians.
Conditions that prevent proper A/C operation, such as full loss of charge, overcharge, condenser blockage, or an open clutch are diagnosed as are conditions that indicate degradation of system performance, such as dynamic high or low pressure, harness breaks in the pressure-switch or clutch circuits, low voltage, or compressor-clutch shorts.
The APAds system collects inputs from two "semi-smart" pressure switches, the evaporator thermostat, electrical supply voltage, clutch, and an internal thermistor. These inputs are processed and result in regulated outputs to the A/C clutch, engine-fan trigger circuit, and diagnostic LEDs. To the vehicle operator, the system's operation is entirely transparent.
There are two modes of operation: Start-up occurs during the first 30 seconds of ignition engagement. For the first 15 seconds, APAds prevents A/C compressor operation and checks each input status. When inputs indicate a safe operating environment, APAds engages the compressor for 15 seconds to lubricate and verify system operation.
In normal operation, which begins after completion of the start-up cycle, APAds performs its preprogrammed compressor and engine-fan control functions.
Current fleet users point to some advantages of the system:
"It has significantly reduced A/C repairs in the spring. . . . It cycles the compressor year-'round, lubricating the shaft and seals every day -- even when the A/C is not on in the winter." -- John Teig, corporate technical rep for Ruan Transport
"If there's a way to protect the A/C compressor and system during the winter, we're certainly going to do it. That's why we spec APAds on every new truck and are retrofitting the module on 200 others right now." -- Nolan O'Byrne, maintenance director, Arnold Transport
For the one-year fleet test, conducted primarily in the Southwest, seven fleets provided 44 pairs of heavy-duty trucks (Freightliners, Navistars, Kenworths, and Volvos) with one truck of each pair retrofitted with APAds. Final figures showed major mechanical A/C expenses -- clutch, compressor, or dryer replacement, as well as system evacuation and charging -- were 65% lower in the trucks with APAds.