We have had this unit for 3 years. We have had it serviced with freon and cleaned each year. The problem is that the air blows out of the vents but it is not cold. Well, for example, it was only 78 outside and I had the air set on 72. It would not give us that 72 degree temp. The doors and blinds were shut. This continues to happen, Before we purchased this unit, we had a train. There is a panel under the house that is the original from the train. Why is the unit not able to cool the air to even 72 when it is only 75 outside? This has continued to happen and we have had many heat and air men over to clean, etc. Please advise. Thank you for any assistance.

Hello
The only possible reason i can think of is the capacity of your a/c unit is not enough.

A larger capacity unit will give you more cooling power.Capacity is based on heat load or how much heat can be removed in a certin time to give you a certin temp.Say you have a 3 ton unit doing your home,you may need a 4 or 5 ton.

There is usually a 3 to 4 degree swing in temp or difference.So if its 75.f out and you have 72 inside.This is not bad.Some units will not cool with a outside temp of 72.This is a limitation for most household a/c units.

Have someone do a heat load calculation of your home and see if your unit is big enough.

Your problems could be varied,eg:
Poorly fitted airhandler panels under the house drawing in ambient air.
Low on freon.
Dirty coils.
Heat strips engaging when calling for cool.
Uninsulated refrigerant tubing.
If you continuously have to add refrigerant your airhandler coil under the house is leaking.

Hello, it is possible that the unit may be undersized for you home and not being able to keep up with the indoor heat load. The only way to determine thia have a hvac contractor do a cooling load calculation on your home. I have seen many units undersized that cause this problem.