My home a/c tech said the coils were blocked, preventing the addition of freon. How can coils be blocked?

Question

My home a/c tech said the coils were blocked, preventing the addition of freon. How can coils be blocked?

Answer 1

a unit will not take refridgerant if the evaporator coils are clogged the inside coil dirty evap coil he should pull and clean both inside and out side coils depending on difficulty level and age of evap coil if its old you should replace it the guy above me dosent work on ac system for a living i do its not about gas its about air flow

Answer 2

I doubt you heard him properly.

The coils in the condensing unit (outside) may be dirt blocked to the degree insufficient air flow is preventing adequate cooling.  Cleaning the coils will fix this.

The coils in the evaporating unit (inside just above the furnace) may be blocked due to ice build up.  In this case the air flow is inadequate; clean filters and make sure you have sufficient air flow.

Freon is a refrigerant.  There are other refrigerants as well, and the proper refrigerant for you is governed by system design.  The refrigerant condensed in the condensing unit where pressure is applied to the gas phase refrigerant.  The liquid refrigerant is transported to the evaporating coil where it expands back into the gas phase, cooling the coil and then the air that blows over it.  The gas is then returned to the compressor and the cycle continues.  This is a closed system so it is not likely dirt would block this closed loop and block refrigerant flow.

Refrigerant is added at the compressor unit; if it is dirty, it needs cleaning which is easy to do and refrigerant addition is pretty easy to achieve so I do not see how any blockage of the fill valve by dirt prevents refrigerant addition.