We had 3 people out with 3 different answers. We have a 2700 sq. ft. home with the Lennox 13hpd-048 4 ton system. One day the it just starting blower warm air. One place came out and said it was the coil, txv valve and something else. He did a leak test but didn't find anything. Actually let some Freon out to test his unit out. The next person said it was just the coil. The next person said it was just the txv valve. Well we went with someone that was recommended but he was busy so he sent his son. Seemed to know what he was doing but very unprofessional. He replaced the valve and charged me for 12 pounds of freon. A couple of days later it stopped coiling again and said we didn't want his son coming out. The guy came out and re position the bulb on the outside of the upper unit and wrapped it. The house has been cooling great but the outside unit started making noise sometimes when starting. Im just trying to give as much info as I can. The pressure on the system has always been a little low. I was told because it how the pipe was run. It was something like 60-65 on the low side and over 200 on the high side. I was told it was supposed to be somewhere about 70. This was based on some of terms I read such as outside air, super cooling etc.. After 3 different answers not sure who to trust. I was told it was high pressure, filter dryer needed to be replaced or a couple of other things. Just looking to be more informed when I call the next company in.