Last summer when we had the really hot days of 90-100 degree temp outside my a/c system would not cool the house below 80 degrees inside and the unit would run constantly I decided today to check the system I put my guages on the cond. Unit and had a suction pressure of 45 and a discharg pressure of 185 the temp outside was 80 degrees and the inside house temp was 78 degrees , I checked the air temp above the evap coil and it was 52 degrees , why does this unit work OK until high outside temps.

Clean the outside unit. It is probably dirty and when it is real hot cannot disapate the heat generated.

Is your filter and evaporator coil clean? With a 45 lb. suction line pressure, 185 highside pressure, 26 degree deference between the return air and discharge air temperature indicates low air flow through the evaporator coil. Your pressures are to low for a 80 degree day. Your system may also be overcharged, you need to do a superheat check after you check air flow. On a hot day when the system doesn't shut off and you have a 26 degree delta T. you are probably freezing up the coil.

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Originally Posted by JackT

Is your filter and evaporator coil clean? With a 45 lb. suction line pressure, 185 highside pressure, 26 degree deference between the return air and discharge air temperature indicates low air flow through the evaporator coil. Your pressures are to low for a 80 degree day. Your system may also be overcharged, you need to do a superheat check after you check air flow. On a hot day when the system doesn't shut off and you have a 26 degree delta T. you are probably freezing up the coil.

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Thanks for your info jackt I will do a superheat check to see if the system is overcharged, my filter is clean I maintain that on a regular basis. And the condensing unit is clean as I usually wash that out at the beginning of every season.

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Originally Posted by hvac1000

Clean the outside unit. it is probably dirty and when it is real hot cannot disapate the heat generated.

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Thanks for your info hvac1000 but the condensing unit was clean , I wash the coils out at the beginning of the season.