People ask, “What’s the most frequent home maintenance problem you find at a typical home inspection?”
When I answer, “The A/C evaporator unit,” many people scratch their heads, looking puzzled. They don’t know what I’m talking about. The folks who do know what I’m talking about are always surprised, because they think this item is taken care of when the air conditioning gets serviced once a year. And it should be, but many cooling system technicians never remove the evaporator cover, much less clean and service it.

If you don’t want to take the time to read all the details below, here’s the bottom line: Tell your service technician to include the evaporator coils in his servicing and to report the condition on the itemized service invoice.
For those of you who want the long version, let me explain.
The evaporator is the inside component of your cooling system. Some people call it the A-coil or evaporator coils. It’s the part that is located physically on the air handling equipment inside your house.
It’s always inside a metal cabinet, with an inspection or service panel that must be removed to get to it. And that panel is one of the reasons that it gets neglected. Many times the evaporator is in a hot attic, and the panel has several screws, and it’s hard to find the last screw holding it on, and the panel never goes back on as easily as it came off, and …. You get the picture, right?
In short: the panel is a pain in the katoosh.

But here’s the problem: the evaporator coils are a critical component for the system, and these coils take the most abuse, because they get wet from all the moisture the system is removing from your house. WET!
Moisture means abuse on metal parts. Copper corrodes and gums up and will develop pin holes and leak refrigerant. And all that moisture will clog up the system. The moisture has to be removed from the system on a routine and systematic way.
So home inspectors frequently find the evaporator in bad repair. Sometimes there is even water dripping into the overflow drain pan under the evaporator. If the home owner is lucky the water is dripping at the exterior secondary drain line. If they are unlucky, the water has dripped out onto the ceiling under the evaporator, and there is a huge water stain on the ceiling in the house.
The water is the problem, but it could have been taken care of if the service technician had taken the few minutes required to examine and clean the evaporator coils while he or she was checking the air handler equipment.