unix-freak wrote:
Greetings,

An AC man came out checked my system a few days ago and I was told
that I needed a bigger compressor/furnace.

Basically, it was 85 or so outside and 80 inside and no hope of
getting any cooler inside. Compressor output air temp was 99 with the
coil's input at 91. The compressor has a deck over it (was like that
when I moved there). There is 3 feet above the deck. He checked the
charge and said it was good.

Inside supply air was 70 degrees. Surface mount attic fan had stopped,
so the attic was 150 or so. The fan's bad so I'll replace it today.

Anyway all that to say, the AC guy told me that I needed to go with a
5 ton unit for my 1800 square foor home. I have a 3 ton unit now. It's
a Trane and the house is 21 years old.

What did his Manual J heat gain / loss calculations show that you need?
He DID do a Manual J, right? If not, call another contractor.

What is the return air temperature measured at the registers?
What is the return air temperature measured at the air handler plenum
(return side)?
If there is more than 2 degrees difference between the above two
readings you either have a leak or inadequate insulation on the return
ducting.

What is the supply air temperature measured at the air handler plenum
(supply side)?
Subtract the last two - What is the delta-T (temperature drop across the
air handler)? Should be 17 - 22 degrees. If it is outside this range
then I'd call another contractor.