Air conditioner cannot cool down to below 80F during afternoon

Old 08-08-14, 03:24 PM
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Air conditioner cannot cool down to below 80F during afternoon

I bought the house in winter, and did a HVAC inspection at the time. The HVAC company said that evaporator coil needed to be replaced, so I had them do the repairs. In summer, I found out that the air conditioner was not really working well. When the outside temperature is about 95F in the afternoon, it cannot cool the house down to below 82F. So I called the HVAC company and had them check for me. They said everything is fine except that Freon is low. They said it is normal that they could not figure out the accurate amount for the Freon when they do the job in winter. They added some Freon, and the air conditioner seemed to be fine for a few days. However, now again it cannot cool the house down to below 80F. I did several tests. If I turn on the air conditioner in the afternoon when the room temperature is about 88F, it can cool the house down to 80F within an hour. However, the temperature just won't drop any more. It will only drop when the outside temperature becomes lower in the evening. I also measured supply air and return air. When the return air is 83F, the supply air is 68F. However, when the return air becomes 80F, the supply air remains 68F. The temperature of air coming out of condenser is about 110F when the outside temperature is about 95F. I am wondering what could cause the problem. It is a 14 years old Trane 1200. Thanks!
Old 08-08-14, 05:53 PM
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I would measure the return air at the grill and measure the return air a few inches from the evaporator coil. I'd expect ~ a 3 degree rise if the duct runs through a hot attic but 9 or 10 degrees would indicate a return air leak that must be sealed.

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