Cleaning the condenser coil. This has always been the number one task that Service Technicians avoid at all costs when maintaining residential equipment. Maybe it is the nature of the fast paced business when the weather gets hot? Certainly it could not be the lack of water to rinse the coil as there is almost always is a water spigot on either side of the home. I cannot figure out why, and this may be one of the largest aspects of seasonal maintenance that impacts the efficiency of the unit. Sure, the system will still operate if not cleaned, for a while. Lets explore just how the capacity and EER are impacted...
A/C Expanded Cooling Data
For an air-conditioner operating at design load, lets estimate 85F for simplicity, the condenser can deliver close to the nominal capacity. Remember, nominal capacity is in tons, from 1.5 to 5 tons, in half-ton increments for residential equipment. There are 12k btu/hr per ton. In my example equipment, the unit is 36K btu/hr or a nominal 3 tons.
When a condenser becomes dirty or fouled, the unit cannot easily reject heat from the refrigerant. This in turn drives up your liquid line pressure and the system artificially operates at what can be determined a higher outdoor ambient than actual.
Guess, what? The condenser never gets cleaner without someone doing so! Therefor, the capacity losses only get greater throughout the season.
Heat Pump Heating Data
For a heat pump, the penalty on your electric bill might be more severe - particularly in a cold climate like New England. As the condenser coil gets dirty, a heat pump operating in heating mode will begin to decrease in capacity just like an A/C.
One phenomenon I have yet to fully understand is the Heat Pump Mini-split. Don't get me wrong, I have installed tons of these systems over the past 15 years. But, these heat pumps tends to keep themselves clean in New England! I think it has to do with the micro channel coils and long heating seasons; they almost wash themselves off every Winter, and stay clean enough through the Summer.