Cleaning air conditioner condenser and evaporator coils is a basic need for proper system maintenance. In fact, it is probably the number one performed maintenance task by air conditioning service technicians. It seems, however, that with the entrance of so many manufacturers and packagers of coil cleaners, that some of the facts about coil cleaning have been lost. As a premier supplier of coil cleaners for the trade, we will discuss in general terms why coils need to be cleaned. The discussion is with aluminum-finned air conditioning applications, but the principles also apply to refrigeration applications.
Both condenser and evaporator coils are made for one purpose - to transfer heat. The evaporator coil (indoor coil) is generally designed to pick up heat from the inside air, and the condenser coil (outdoor coil) is designed to give off this heat to the outside air. The exception is a heat pump application in the heating mode where the functions are reversed. As dirt, hair, lint, grass, grease and other contaminants coat the fins and tubes of the coils, the transfer of heat is reduced and system problems increase. A dirty evaporator coil causes less air movement over the coil which results in less heat pickup for the refrigerant.
If the heat pickup is not sufficient to vaporize the refrigerant, then one of two things typically occurs: 1) Liquid refrigerant travels back to the compressor and will either wash the lubricant off the bearings and lock the compressor or cause the rotor to drag on the stator and cause a compressor burnout, or 2) liquid refrigerant travels back to the compressor cylinders and the hydraulic pressure breaks valves, typically the suction valves. In the case of a dirty condenser coil, the reduced heat transfer results in higher than normal head pressure and discharge temperatures. This condition causes the compressor to work harder to pump against the higher pressures. The end result is the compressor motor overheats and wears out prematurely.
In either case, a dirty condenser or evaporator coil, the compressor is the component that is usually affected the most, not to mention that in both cases the cooling capacity of the system is reduced, resulting in higher electric bills. For these reasons, it is important that both condenser and evaporator coils be cleaned at regular intervals.
Accumulated dirt, dust and grease insulate against heat transfer. Dirt prevents the condenser coil from rejecting heat as it was designed and elevates head pressure. When head pressure rises, so does electricity because of power requirements.
Higher head pressure also reduces system BTU capacity, by as much as 30%. A 10-ton unit may now only be capable of providing 7 tons of cooling. This causes an increase in runtime and inadequate comfort cooling or refrigeration.
Increased amperage draw combined with longer run time adds up to much higher energy bills. A 10 ton A/C system operating for 1500 hours could use as much as 37% more power when the coils are dirty. With a kWH cost of 8.3 cents this would cost the owner $618 more to operate (or $62 per ton more with dirty coils).
For more information see Catalog G-1 Chemical, Lubricants and Accessories.
For more articles on climate control:
Compressor Overheating is the Number One Refrigeration Problem
HVACR Tech Tip: What You Need to Know About Flooded Head Pressure Control