On Being Cool
“I need an AC for a 4106”. It was Violet from Mussel Shoals AL, one of my favorite parts customers.
“Which parts?”
“ALL of them. You know that switch you’re NOT supposed to use when the bus is moving? My driver DID, and the AC spilled its innards all over the road”. These buses used a Chevy truck clutch to drive the AC compressor, but engaging it when the engine was wound up was disastrous.
A really clever guy would have written this months ago (then it might have been useful), but what the heck, here are some things to consider as hot weather approaches.
You might want to have a Drivers Meeting to do some training on how you want the AC used, and how to work the systems in your buses... WITHOUT dropping them on the tarmac.
In addition to teaching idling laws (and the fact that you don’t want drivers napping in an empty bus with the engine running) you may want to discuss how long before a pickup they should start the engine. Different buses may cool down faster. They should understand how the drivers AC and the passenger unit can either supplement, or interfere with each other. Opening and closing fresh air vents can make a difference.
Modern AC units are so powerful that they’ve given birth to the evil sine-curve. This phenomenon happens when a passenger complains about being too cold, and the driver changes the thermostat in a big way. Soon the bus is hot, so the driver cranks that puppy the other way, and soon the temperature is going up and down like a roller coaster. Using the term sine-curve makes me look sophisticated, but the solution is to make small changes and wait. Drivers who understand how thermostats work are more likely to get it right.
Newer AC’s sometimes display a code when they fail, which a trained driver can read, and give you an idea of what’s wrong.
Finally, when there is an unexplained failure in a modern system, sometimes turning the electrical system off, then back on, will re-boot it successfully. It’s worth a shot, but don’t go too far. One definition of insanity is doing the same thing over and over… expecting different results.
Most operators go through their HVAC systems in late Winter, because their buses aren’t that busy, and Spring almost always comes next. In addition to the obvious, like checking refrigerant levels and replacing both Freon and air filters, it’s worth looking at some less obvious items that sometimes behave badly.
In the back of your bus are some flailing belts. Turn the engine off and check them out. Some belts only turn fans, but one brute is turning an AC compressor which requires lots of horsepower. Check, and preferably, replace it, because it has a right to be tired. Take a peek at the compressor mounts and brackets.
While you’re there look for any signs that the compressor is leaking, or that Freon lines are either chafing or cracking.
There are lots of little wires back there. I have no idea what they do, but CAN tell you that when they break, bad things happen. You may want to make sure that HVAC wires that have been resting all winter have tight, clean connections so that when your driver requests AC, something cool happens. If a compressor clutch is old, replace it now, before the Bus Troll gets a chance to mess with it.
You’ll want to clean your condenser, and make sure that winter salt hasn’t eaten TOO many of the fins.
It doesn’t matter how cold your AC chills the air, if it doesn’t make it into the passenger cabin, so periodically it’s a good idea to clean out the ducts. In some coaches they’re part of the sidewall, in others the package rack. In every case, if they are full of candy wrappers and trash, your AC is not going to work. Where applicable, check the return ducts too.
Make sure your electrical system is in good shape (I know… we say this at the beginning of every season). Complying with idling laws means more starts and stops, and your AC is sucking lots of current for hours on end, so check your alternators and batteries. Alternators grow less efficient when they’re hot, so just when you need them the most, they’re getting tired. Batteries tend to use more water in the heat.
Most modern AC’s use multiple motors to drive condenser (and often evaporator) fans. Some of them may not wake up after hibernating all winter. In summer, you need them ALL. Manufacturers rarely chunk in an extra couple just for the heck of it.
Your customers will tolerate all sorts of indignities, but heaven help you if the AC doesn’t chill them out. We old geezers tend to faint when it gets hot, with big headlines to follow, and nothing shouts POOR MAINTENANCE like a coach cruising down the highway on a warm day... with the roof hatches open.
