Get Tech Tips
Subscribe to free tech tips.
Checking Evaporators on Furnaces
In Florida, there are not many gas furnaces—at least not as many as up north. Sometimes, we can look like real dummies compared to techs who work on them every day.
One thing to know about 80% gas furnaces with cased evaporator coils is that you can often check the evaporator coil by removing the high limit and running an inspection camera up through the opening.
You may also be able to use a mirror and flashlight, but you usually won't see much due to the heat exchanger being in the way. Otherwise, you are stuck removing the entire blower assembly, and that's no fun at all.
Another practice is benchmarking the static pressure drop across a new coil when it is dry and wet when installed or during the first service call. You can then easily watch coil loading over time without the need to look at the coil visually.
Just make sure to turn off the power before removing limit switch. Or it’s like playing operation pulling it out without shorting against the sheet metal.
When I install a cased coil on a gas furnace, I like to cut out a panel on the casing. Plexiglass works well for a window but usually doesn’t provide a solution since you generally cannot see the bottom side of the coil without removing the coil I spec tip. Plate. So, get you sone sheet metal, some duct liner, or 3/4 inch padding made by Armaflex, (what I like best), and make your own window when you install it. If you did t install it and you have to pull the coil to clean it, what’s an extra 30 minutes to save you an hour and a half the next time you service that unit. Just saying.