I got sent to replace the tandem scroll compressors in a York RTU (mid-age 10-13 years). One of the compressors in the old pair grounded out.
Recovered, removed old compressors. Cut out old liquid line drier. The old driers (machine has two circuits - four compressors) were installed about 4 inches upstream of the TXV's.
Since we figured there might be goodies in the system from the burnout we wanted to be able to change out the drier easily, so I installed valves before and after the drier and flared the drier in. Remember, one of the brazed joints was very close to the TXV - after cutting and all I'd say that the joint was about 2 inches from the TXV stub.
I used thermal paste between heat and TXV and also wrapped the TXV with a wet rag. In hindsight, I think I should have removed the guts from the thing. Anyway, rana little N2 through while brazing and put the whole thing back together.
Filled with 150psi N2, checked for leaks with bubbles...none found. Evacuated...system held @ 300 microns for an hour.
Weighed in factory charge. Checked compressor phasing and started the thing up.
After several minutes of running, pressures were: 50psi suction, 110 psi discharge. Thought maybe the diagram had the colors of the wires wrong for the compressors and they were running backwards...reversed direction...noisy, very minor differential. Back to original (proper) phasing...same pressures (50 / 110).
Return temp during all this was about 80*F, supply temp (I was only running the new compressors) was 58*F. Good airflow. Noticed some frosting on the distributor tubes.
Hit me with your thoughts....did I overheat the TXV? (it can't open enough anymore) I don't think there's junk in the system...I'm conscientious about reaming, cleaning, and purging with N2 when I braze.
Looking forward to hearing your ideas...