thermoKing SB-300 Charging

[OldSchoolJeff]

Hi All, I'm new to the site and have never worked on a transport heat/cool unit.(I have 20yrs in hvac/electrical repair) Yesterday I was talked into charging this unit, since I do work for this winery and this unit is on their mobile bottling truck. I really wanted to wait and contact the factory for proper procedure but wound up recovering the charge, weighing it, and then put back in the nameplate 16 lbs. R404a. I removed 11 lbs and added another 5lbs. They said it was low because liquid was no longer visible in the sight glass and the run/pulldown times had gotten longer.

During recovery/charging, I used the access ports on the compressor:discharge king valve and lower crankcase suction port. I didn't have the unit powered up, and I didn't use a third hose to the receiver king valve, nor did I energize the upper solenoid valve(trv?) or the changeover valve.

Did I make a mistake and trap ***** in the system, which would mean I'm now overcharged? I noticed the running pressures (55 deg F ambient) were 50/250 cooling, and 70/400 heating (high idle) 400 seems too high to me, but no background in diesel powered compressors. I did notice the liquid level show up in the middle of the sight glass and float the ball, so it would appear the charge is correct.

Any thoughts???

Jeff

[cadwaladr]

i think you did right but i would recover it again,vac it for 48hrs then recharge it with the correct amount of virgin refrigerant remembering only charge in the liquid phase.

[OldSchoolJeff]

Thanks for the reply, great advice since 404a is a blend, the refrigerant percentages are messed up and most likely moisture is in the system which is big trouble for a POE system.

Does the 400 psig head seem normal for the heating mode in a 55-60degF ambient or do you suspect non-condensables?

I think a compressor oil change and filter drier would be good idea on a 10 year old unit also.

[gravy258]

400psi head at that ambient is high.
Do as Cadwaladr states and pull out the charge,
Then change the dryer and vac it out to below 1000 microns at least.
Then recharge as a liquid to the high side with the unit stationary, then running and feeding the rest in to the suction.
You don't need to power up any valves up on a SB300.

The ball half floating suggests a undercharge, or more than likely a dirty condenser coil.