got a 12yr old lennox split system 2 1/2 ton. A-coil will only get half way cold.
..recharged with r-22. pressures are perfect, about 80 low and 225 high but no matter how much more freon i put in the pressures keep going up but the line set temp wont come down, stuck at about 80 degs.
..it was running about 325 on high side before i replaced the dryer and was causing the compressor to over heat and shut off but still the a-coil will not flood with freon and will only give me a 10 deg temp drop across the coil.
I doubt the 325 head pressure by itself, would have caused the compressor to overheat (unless the outdoor coil was restricted), so the superheat was probably high initially. And the fact the head was high could suggest someone before you had overcharged the system, in an attempt to get the superheat lower.
If additional refrigerant raises pressures but doesn't decrease superheat, I'm thinking distributor tube restriction, which is a thin theory. But I've never seen an unrestricted fixed metering system that wouldn't eventually load up the coil, if you add enough refrigerant.
Disable the blower motor with the condenser running and see how the coil loading goes.
I will say air flow is MOST DEFINITELY something to check.
Had an almost same situation today, low TD, low pressures, warm coil, SH & SC off and they wanted on one of our maintenance policies.
Mind you, this unit was installed as a package with a furnace in 1995 by others. We have serviced the furnace since 2002, but only replace the capacitor in the outdoor unit and nothing else done according to the service sticker.
Well it was a 75K furnace with a 1.5T a/c with blower tap for cooling on high.
I found an old invoice with a reading of 11555 CFM, 50/120 PSIG, 74° AMB and a
16° TD. This was also after he added a LB of refrig because he replaced the core due to a leak( maybe low pressures due to improper, too much, airflow?).
Duct work is spotty at best.
Lowered to heat tap, which was 752 CFM, lowest possible, got a 16° TD, but it is, was and will always be WRONG!!!
So YES airflow matters!!!!!!!
How would I go about measuring actual air flow/cfm?