My mother has a 1971 vintage condo with a through-the-wall compressor and a gas furnace sitting on top of the air handler in the hall. About a 1,200 SF ground floor apartment with 2.5 ton straight cool unit. The compressor died and I was told this type were not very high efficiency, and only one type was available. So I had it installed, but decided not to replace the air handler. Electric bill went from $125 to $300 a month. A/C guy said units mismatched, even though both same size, new one is more efficient SEER than the other, so I replaced the air handler. No change in the electric bill. Still $300 a month. He was out several times, no answers, says all pressures are correct, but air temp not getting as cold as it should but no reason found, blaming in on location of compressor at inside corner of L shaped building that does not allow for good air circulation at compressor. But old unit ran fine for 30 years in the same location.

Any ideas? I tried two other A/C guys who both said unit seemed to be within specs.

Get a thermometer and check the temp of supply air,, not knowing the layout, if you can also check temp. of the return air,, tell us and lets go from there

wmproop has a good start... also what state do you live in?

Thanks! I will check the temps this weekend. The condo is in South Pasadena, Florida, which is west St. Pete.