By Steve Schaeber
It’s one of those basic acronyms we learned in tech school: Keep It Super Simple. You may have learned slightly different terms, but the idea remains the same, and refers to something known as Occam’s razor. Devised by William of Ockham in the 14th century, the principle says that when considering competing hypotheses, the one with the fewest assumptions should be selected. In other words, all things being equal, the simplest solution tends to be the right one.
Usually when tackling an HVAC performance problem, the first things technicians go after are the big ticket items: compressor operation, radiator / condenser issues, heater core / evaporator condition, control panel function, blower fan output, etc. Rarely are cabin seals thought of as a primary suspect. But really, what we’re trying to do with an HVAC system is heat or cool a certain volume of air. If that amount of air is increased or decreased, system performance will be affected. Mobile HVAC systems are designed according to cabin size, so consider this: can a heater be effective if a door is left open?
Lately I’ve come across a few seal issues that have taken their toll on system performance. If you check out the MACS Blog at macsworldwide.wordpress.com, you’ll find a post from Chris Tyson where he repairs a backhoe door seal at R&S General Contractors. He explains that he first suspected a system problem, such as a clogged heater core, causing poor performance during engine idle. However, it turns out that deteriorated door seals allowed so much cold air in that the heater was not able to keep up.
My neighbor Mike has three Chevy Astro vans, which have a doghouse engine cover in between the front driver and passenger seats. Where this cover mates up to the firewall, there is a foam rubber seal around the edge. Mike explained the heat in his 2001 van had not really been that great. So, he took the van to his regular shop, which concluded the blower fan was not spinning fast enough. After an unnecessary motor replacement, the heater was still not up to snuff, so the technician dug deeper and found that the cover and seal had been misaligned, creating an open gap through which air could escape.
Seals are so simple, they are often overlooked. But just like we seal the doors and windows of our homes, we should consider the important role they play in mobile systems as well.