Is the duct work and HVAC equipment located in the attic?

Mike, the answer to your question is yes. Only the compressor is outside. Also there was a clogged line that was blown out with nitrogen and the inline filter/drier and TXV were replaced at the same time last month. I also have a thermostatically controlled attic fan set to 110 F but the temperature in the attic did not trigger it.

Is your system not working as expected or are you concerned only about delta-t because you think it is improperly charged.

I'm not sure that my system is working properly. I would expect that regardless of the outside temperature, the differential between inlet and supply would stay relatively the same. I don't think an improperly charged system would result in an 18 degree delta. After the replacing of the TXV, 10 days later the compressor would not turn on because there was a leak at the TXV and all the refrigerant leaked out. The leak was repaired and the unit recharged. The need for cooling during early summer has been spotty in Northern California where I live and the system goes for days or weeks without needing to cool.

Thanks, mike. I did a test today and at 9:30 am with an indoor temperature of 74 F and an outdoor temp of 64 F the differential was 18 degrees after 5 minutes so it looks like you diagnosed the problem correctly.

Another problem could be the attic fan itself. They can create a negative pressure that sucks air into the attic from the house. That air needs to be replaced so outdoor air is pulled in from the leaky parts of the house structure itself. Or, indirectly in the attic from less than completely sealed areas of the ducts and duct connections and the blower equipment itself.

I'll bet the AC will work better with the attic fan turned off.

The fan was not operating when I made these measurements as none of the days temperatures caused the attic to reach 110 F. Also the system has been operating very well for 14 years (knock-on-wood) with the small roof mounted fan that just keeps the attic from getting higher than 120 F. This season was the first time the A/C was not working due to a clogged refrigerant line. However, thank you for your suggestion, Elmer.

Today the temperature was 90F. The fan came on just about the time the outside temp reached that mark so the attic is about 20 degrees above outside temp and the inside temp is about 78F. I measured the inlet to supply air differential after 15 minutes and it was only 9F. I'm wondering if the attic fan is too small or if I need a second one.

Don't add another attic fan. The general consensus is powered attic fans cause more problems than they solve. I have one in my attic and i can't say for certain if helps decrease my cooling costs.

Outside temperatures are measured in the shade. So if the outdoor temperature is 90 degrees, the roof deck in the sun will be well over 100 degrees. Your attic temperature of 110 degrees is not as bad as you think it is. in my opinion the powered attic fan is the most useful when the sun goes down. Then it has a chance to lower the attic temperature. Lowering the temperature setting will be help when you are trying to cool the house in the evening.

The fix to your problems is to insulate and seal the duct work. I have never been a fan of duct work in uninsulated attics. But unfortunately many houses are built in this manner to save costs.

Thanks, Kevin for your input. In answer to #2, I watched while the vacuum pump was running and they let it run 20 minutes before adding refrigerant. I have used this company a few times before. they are factory authorized service for Carrier in my area and actually did the original installation. I have never had a problem and the techs always seem knowledgeable and they pay attention to detail. You're comment about the TXV bulb was similar to one of my thoughts on the situation. I will wait for cooler weather to check it.

The house was built in 1991 by a custom builder. The attic is well insulated with blown in fiberglass and the ducts are covered with insulation. I have read several articles by HVAC companies that HVAC systems are not efficient around 100F and are optimized for the average summer temperature range in the area. The articles say that if the outside temp is 100F and the HVAC system is keeping the temperature at 80F or lower, you have a good system. I am using a Honeywell programmable thermostat and when the outside temp is 100F the system maintains 78F inside easily with only a 9 degree delta from inlet to outlet. It usually runs about 5 minutes until the thermostat turns it off and then comes back on 15-25 minutes later at those temperatures so the house is comfortable, but not cold like in an industrial building or retail store. As the outside cools, the system comes on less often and the delta increases to a max of 18F.

The only issue I am still concerned about is the condensate line. I was only able to catch about 2-3 tablespoons of water over two days where the RH was 18-25% which is quite dry heat. I'm not sure there is an obstruction since I hooked a strong shop vac up to the outside line and sealed the connection well with duct tape. After 5 minutes where I could feel the PVC pipe get colder than the outside air, all I got was some debris and a few drops of water. I'll wait for a more humid day to check again.

Thanks, Kevin. The system can maintain a comfortable 76-78 with low humidity and temps between 90-100. It does not seem to be straining to cool even when the daytime outside temp is hot and the inside differential is lower. The temperature trips the thermostat off after 5-7 minutes of cooling. The compressor and evaporator are 14 year old so the compressor is most likely not as efficient as it was when newer. I was hoping to avoid a total replacement as we are looking for a new property. The tech who came out to replace the TXV did use an amp meter to check the system before and after but he did not mention any issues. We had his company quote repair or replace and they did not tell me that they recommended replacing the unit.

"when the outside temp is 100F the system maintains 78F inside easily with only a 9 degree delta from inlet to outlet. It usually runs about 5 minutes until the thermostat turns it off and then comes back on 15-25 minutes later at those temperatures so the house is comfortable,"

I have more than 40 years experience and I'll believe that when pigs fly. You are reading and/or relating data wrong. I've compared thousands of deltas and at 15F with 100F ambient,a unit will run almost non stop to maintain 78F room temp. Even if a unit was grossly oversize it would struggle if delta was 9F. Aside from all that,exactly what is your complaint since you state temp is being maintained at set point of 78F with low humidity?

Kevin9408 & Klem 1. PLEASE DO NOT RESPOND TO ANYMORE POSTS. You are not being helpful to me and if you don't have anything positive to say then go somewhere else. I started this post to understand if my A/C was operating normally and I want constructive responses not two people acting like juveniles looking for a fight.