Where to look for cooling coil problems: First, make a visual inspection of the cooling coil. Most air handlers provide an access panel or cover that can be removed to give at least partial view of the cooling coil surfaces. Turn off electrical power to the system to be safe from electrical shock. On opening an access cover or panel on the air handler you can recognize the cooling coil from our photos and sketches shown here and elsewhere on this website. You may need to use a flashlight and mirror to see the coil surfaces.
Remember to inspect the cooling coil from the incoming-air side – the side of the coil facing the blower fan assembly. That’s because any dirt or debris entering the coil will come principally from this direction. If you inspect the wrong side of the coil it may look perfectly clean even though it is totally blocked by debris on its other surface. DIRTY COOLING COIL has photos of just how blocked a cooling coil can become in an air conditioner or heat pump.
Here are some common defects to look for at the evaporator coil (cooling coil) in an air conditioner or heat pump:
- Dirt or debris blocking air flow through the coil (DIRTY COOLING COIL)
- Ice or frost formation blocking air flow through the coil (FROST BUILD-UP on AIR CONDITIONER COILS)
- Damaged cooling / evaporator coil fins over more than 10% of the coil surface, blocking air flow (shown in our photo at left in this case, the damage is to a condensing coil, not an evaporator coil). Small areas of damaged cooling fins can be straightened and cleaned-up using a cooling coil comb. Cooling coils with extensive physical damage such as shown in our photograph need to be replaced.
- Evidence of refrigerant leaks (visual evidence may include stains from refrigerant oil left at the point of leakage) (REFRIGERANT LEAK DETECTION)
- Evidence of mold growth on organic debris on the coil or elsewhere in the blower compartment (Mold Growth in Air Handlers)
- Presence of unusual materials on the coil surface such as rodent debris, bird feathers and debris, fiberglass insulation, large trash fragments like paper or leaves confirming a duct or air filter problem. Some of these may indicate potentially serious health risks such as rodent or bird feces and debris which risk bacterial and viral hazards in building air. (Leaks, Rodents In Air Handlers)
- Obvious coil-to-air-handler size mismatch of an add-on cooling coil onto an existing warm air system (ADDING A/C: RETROFIT SIZING)
- Evaporator coil or cooling leaks or holes: if an evaporator coil is leaking (or also if the condensing coil is leaking) you’ll find out pretty quickly as refrigerant will be lost and the cooling system will stop providing cool air. You’ll need expert diagnosis by an HVAC service technician.
- A lot depends on where the refrigerant leak has occurred and what caused the leak. If the cooling coil has a single point leak caused by some mechanical damage (one of our readers accidentally drilled a hole in his coil while trying to drill a drain hole in his air handler), it may be possible to find the hole and repair it using silver solder.
- If the refrigerant leak is in copper tubing anywhere in the cooling or heat pump system that is not too close to an evaporator coil or condensing coil, it should be possible to solder a repair, then evacuate and recharge the cooling system.
- If the refrigerant leak is in copper tubing in or close to the cooling coil (or in a condensing coil) a solder repair is hard to complete because the heat of the soldering process tends to de-solder other nearby connections. It might be possible if the technician is very expert and if s/he knows how to keep nearby surfaces cooled (we’ve used a wet rag).
- If the refrigerant leak is in an aluminum part, soldering aluminum is more tricky and may not be feasible. Ordinary procedures using a torch, for example, just melt the aluminum. Expert welders use inert gas welding methods.
- If the refrigerant leak is due to severe corrosion anywhere in an HVAC system we’re not optimistic that a solder repair is possible. The conditions that caused a corrosion-related leak are likely to have thinned and weakened other parts. The cost of an attempted repair may be wasted.
- Replacement of the cooling coil (or condensing coil) is more often going to be recommended by your HVAC technician because of these difficulties.
Temperature measurements at the cooling coil: see OPERATING TEMPERATURES for a discussion of where and how air temperature measurements are made to diagnose cooling coil or other air conditioner operating problems.
Below we introduce some of the more common air conditioner or heat pump cooling coil or evaporator coil defects and repairs.
Air flow requirements across the air conditioning evaporator coil: if airflow is weak for any reason (dirty coil, duct system defects, blower fan defects, dirty blower squirrel cage fan), the air conditioning system will not operate properly. Some experts write that there should be between 350 and 400 cubic feet of air per minute (CFM) moving across the evaporator (cooling) coil for each ton of air conditioner capacity.
One ton of cooling or heating capacity = 12,000 BTUH so if your AC unit or heat pump is a 24,000 BTUH unit it is a “two ton” unit and needs to see 700 to 800 CFM of air across the evaporator coil.
Some home inspectors and air conditioning service technicians carry a small airflow meter that can actually measure this number with fair accuracy. (The same tool is nice for comparing air flow and balancing air flow at various building supply ducts and registers.
