Ventilation is key
Properly cleaning HVAC units is time consuming, but the payoff is well worth it By Robert Buchwalter
We have all been enjoying, or enduring, an extended hot and humid summer in North America. For those of us in the bus business, images of warm weather, picnics, baseball and fireflies are mixed with dreams of refrigerant bottles, compressors, filters, gauges and unhappy drivers. Our daily write up sheets include the expression “A/C not working” written boldly, often followed by more than a few exclamation points. It happens every year. But this summer’s record setting heat and drought have only increased the scrutiny paid to our HVAC systems, especially by our paying customers. The heat is on everyone’s mind in 2012 and we have to be on top of our game in servicing and diagnosing our HVAC systems.
to inspect the refrigeration system: the compressor, condenser, evaporator, and expansion valve. But this month, I would like to focus on the V in HVACCDT. Ventilation is extremely important in maintaining a comfortable cabin, but it is often overlooked in diagnosis. When it comes to ventilation, we usually look at the amount of air being discharged at the window sills and flowing into the cabin. If this flow seems to be less than normal, we adapt the mindset of trying to force more air into the cabin. But as we look to improve discharge airflow, and passenger comfort, I suggest we also look at the other side of the squirrel cages, to the return air side. Return air is equally important to discharge air. If you cannot pull the air out of
Ventilation is extremely important in maintaining a comfortable cabin, but it is often overlooked in diagnosis. HVAC brings to mind a number of diagnostic disciplines (refrigeration, electrical, heating) that we need to apply in repairing these systems, but let’s look at those letters intently. Traditionally, HVAC means Heating, Ventilating, and Air Conditioning. But for us, it actually means Hot Vehicles Aren’t Chartered. A bus with no air conditioning is clearly a bus down situation. Yet the letters themselves – HVAC – are incomplete. It ought to be HVACCDT, which stands for Heating, Ventilating, Air Conditioning, Controls, Driver, Technician. If we are missing something in anyone of those areas, we will have problems keeping our passengers, drivers, and supervisors cool. Traditionally, a hot bus complaint rives us
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the cabin, you can’t push it back into the cabin. In the Prevost training seminars that Robert Hitt and I conduct, discussions about return air flow center on the Prevost H-Series coaches. The Prevost X-Series: XL, XLII, and X345 coaches have a simple return air system: a single basket placed above the evaporator compartment. The H-Series is a bit more complex. In the H-Series has a return air grill in the stepwell and two return airs on the driver’s side of the coach, at the front and rear. These are the starting points for the ductwork system that eventually delivers the return air to the evaporator compartment. Cabin debris can set up in these areas and begin
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