First, I am a homeowner who has read a lot on this forum including the "For Your Interest" articles.
About a month ago, I had the following installed:
Lennox condensing unit (HSXA19-060) 5 ton, 2-stage scroll compressor
Lennox matching evaporator coil (CX34-50/60C) with factory installed TXV
Lennox 2-stage furnace (G60UHV-60C-110) (high blower fan speed at factory default of 1985 cfm).
I interviewed several companies and tried to choose a good company. I also checked the BBB and the company I chose had no complaints in the last 36 months.
I am concerned about how the intial charging and check-out of the system was done. I tried to choose quality equipment and want it to run as optimally as possible. I also can tell from reading the forum that there may be differing opinions on what is the best way to do it.
The company I used has a service tech come out after the installation crew finishes. When the technician came out, he put the unit in 2nd stage cooling by lowering the thermostat temperature to a very low value and letting the system run for several minutes, He put his pressure gauges on the condensing unit lines. He next used a thermometer to read the outdoor temperature about 2 feet away from the unit. He read 80 degrees F. He then looked at the table on the condensing unit panel. He showed me the following:
For Outdoor coil Entering Air Temp (degree F) 75 degree F ---- Liquid = 291 and Vapor = 135
For Outdoor coil Entering Air Temp (degree F) 85 degree F ---- Liquid = 334 and Vapor = 141
The table was labelel "Normal Operating Pressures - liquid plus/minus 10 and vapor plus/minus 5 psig" (also in the installation manual).
Before he put any R410A in, he told me that he read 310 for liquid and 120 for vapor. When he was done charging, he had 320 for liquid and 128 for vapor. I do not recall him taking any other temperatures as are sometimes described in your discussions for subcooling and superheat.
I also looked in the Lennox installation manual. It has a specific section for charging titled "Charging Using Normal Operating Pressures and the Approach Method Outdoor Temp greater than or equal to 65 degree F." This is the only section that talks about how to charge if the outdoor temperature is above 65 degree F. To summarize the section, it says to record the outdoor ambient temperature using a digital thermometer. Next to attach high pressure gauge set and operate unit to allow pressures to stablilize. To charge, use the same digital thermometer to check the liquid line temperature that was used to measure the ambient temperature. For the HSXA19-060 unit, the table in the manual shows that the difference between ambient and liquid should be 10.0 plus/minus 1 degree F.
I decided to do the Lennox approach method (with no pressure gauges) on 2 different afternoons with my Polder digital thermometer (outdoor temp about 97 - 99). The system was running on high stage for several minutes. I put the thermometer on the 3/8 inch liquid line about 2 inches after it comes out of the condensing unit and wrapped it with cloth first then with foam to try to prevent the outdoor air from affecting it. My delta T was only about 3-4 degrees F. I am the first to admit that I may not be doing this right or it may mean nothing.
Is the Lennox approach method what should be used? Am I doing the measurement correctly?
Did the technician do the charging correctly or should I ask for a technician to come back out? Is there a correct way to do an initial check-out and charging for my system? Thanks for your input.