This HVAC central unit was installed in 1991. No maintenance service ppl have ever opened the evap door or foamed out the condenser.

I just opened the evap door and I see that there is NO access to below the coils. Not even from the air handler/furnace. So, I cant even see them. Is it useful to still spray the top side of coils with the cleaning foam? I could only spray 2 of the three coils.

Ive read yearly service should include:

"The underside of the evaporator should be cleaned with a stiff brush. When the coils are free of dust and dirt, clean the tray below the evaporator". I cant do this at all.

So, I dont know if there is a tray or how dirty it might be. Foaming the coils from the top might make the tray worse. Note that the drain works fine. I recently got the manufacturer's installation document online and it mentioned installing a trap. There is no trap in mine and yes I can see the entire line.

So, should I spray them from the top?

evap unit is CAC BDP Carrier model CK5(A,B,P)XW024017

paul