Shine a flashlight through the filter to check its cleanliness. If the light shines through, it’s clean; if nearly all the light is blocked, clean or replace as appropriate.
While the basic refrigerant setups have changed little, today’s air conditioning systems are capable of maintaining a more stable temperature in the cab, truck makers say.
Earlier systems regulated system output but didn’t relate it to temperature. Today, Peterbilt’s latest system has sensors that measure return air temperature, which accurately reflects average temperature in the driver’s environment and cycles the compressor accordingly. Peterbilt project manager David Faw calls the arrangement a “split system” because there are two control heads and two fan and evaporator systems – one on the firewall, and the other in the sleeper under the bunk. Either control can call for compressor operation, Faw says.
Similar improvements have occurred at Kenworth. “We’re always looking to make additional enhancements,” says Jim Bechtold, Kenworth assistant chief engineer. In the past three years, Kenworth has improved driver thermal comfort with a new HVAC control that both oversees the comfort level in the cab and offers an on/off button that gives the driver control of the sleeper HVAC system from the driver’s seat, Bechtold says.
Cool benefits
Improving the pumping efficiency of the compressor and the heat exchange efficiency of the condenser and evaporator generally are considered difficult tasks, and gains may come in relatively small increments.
Fortunately, insulating the cab to reduce heat absorption is a much more fertile area. Improving the resistance to heat flow will drastically reduce the amount of work time for the compressor – and related fuel consumption. Shorter on-cycles and longer off-cycles also may carry with them a small increase in system efficiency since the condenser then can remain closer to outside temperature; the result will be a positive effect on fuel bills.
“Fuel consumption and how it impacts the environment are important priorities at Kenworth,” says Bechtold. “We reduced the need to run the A/C system by enhancing cab insulation and sealing, and adding slider windows in the sleeper for increased fresh air circulation.”
Side benefits occasionally come from anti-idling technology. The Peterbilt Comfort Class no-idle sleeper A/C system utilizes an improved insulation package that includes a radiant barrier, which gives the walls and roof “a much better R-value,” Faw says. Obviously, such an insulation enhancement also will reduce the energy required to cool the cab and sleeper while running down the road, and also prolong the life of the A/C system’s components.
Peterbilt also offers an optional thermal package for the cab and sleeper without the Comfort Class system to “keep the compressor from running as much,” Faw says.
Maintenance matters
Technicians once deemed air conditioning maintenance a nightmare because truck equipment had been derived from the less demanding auto world, but that’s no longer always the case. “Kenworth is constantly evaluating reliability to reduce the frequency of maintenance and its cost,” Bechtold says. Recent improvements include upgrading the A/C compressor components for longer life and simplifying the HVAC unit air distribution components, he says.
Similar work at Peterbilt has taken air conditioning system reliability far enough ahead that Faw sees a drastically reduced need for routine maintenance checks, such as attaching refrigerant gauges and checking operating pressures annually. “We’ve seen a tremendous reducing in the PM requirement in recent years,” Faw says. “Often, the best approach is to just be prepared to fix the problem immediately when you experience reduced cooling.”
Faw believes that one of the few worries today is making sure the compressor cycles regularly in winter. In most climates, the problem takes care of itself when the A/C operates in conjunction with the defroster. Where longer dry spells occur during the winter, the driver should cycle the unit on for five minutes or so once or twice a month.
Bechtold thinks the most critical A/C maintenance issue lies with the technician himself. Kenworth offers an HVAC training and certification course for Kenworth dealer-sponsored fleet technicians, he says. “We focus on understanding the proper diagnostic procedures, running performance checks and troubleshooting the A/C system.”
Routine checklist
Unless a technician can deal effectively with the safety issues related to A/C service, and understands what mechanical problems lead to poor performance and certain kinds of upsets in system pressures, air conditioning service likely will end up costing far too much.
Frank Burrow, warranty and product support manager for Red Dot Corp. – a maker of A/C units and replacement parts – suggests some routine maintenance operations that will help forestall breakdowns and improve system performance:
- Check the sight glass on the receiver-dryer. Within the sight glass, there is a dot that indicates moisture level. Moisture is a critical problem because refrigerant is “hygroscopic” like brake fluid and draws moisture out of the air even though the system is pressurized. A blue color signals a clean system with dry refrigerant; pink, white or gray indicate moisture. Refrigerant is not equipped to handle moisture such as engine oil. Moisture reacts with what’s in the system to produce acid. For this reason, the system starts corroding and gets into serious trouble shortly after moisture enters.
- Check the condenser to make sure it’s clean of bugs and debris, and that the fins are straight. Flush at low pressure with water to clean, and use a fin comb to straighten bent fins, as they inhibit airflow and heat transfer. Make sure the unit and its hose connections are mounted securely to prevent vibration, which often produces leaks.
- Inspect the in-cab and in-sleeper air filters. If light can’t be seen through them, replace them or, if appropriate, clean them. Proper filter maintenance will improve performance and also keep dirt off the evaporator. Clean the evaporator with an appropriate solvent in the event filter problems have allowed dirt to coat the fins and/or clog the areas between them.
- Check the compressor clutch for trouble by listening for noise and feeling cautiously – with the engine off – for high heat, which indicates slippage. Replace if necessary.
- Inspect the drive belt for cracks or glazed surfaces, replace if necessary and set belt tension with a tension gauge. Also, check wiring to make sure insulation is sound and connections are tight.
- If a system is opened up, put some of the system’s oil in a clear container and compare it to new oil; if the lube has lost its clarity and turned amber or brown, that’s a sign of trouble. Always replace any oil that was drained, and if the system is contaminated, it must be cleaned out thoroughly, evacuated – for moisture removal – and recharged with the proper amounts and types of both oil and refrigerant.
