Lennox RTU
M#LCH036H4EN Y
S#5611H05061

Copland Scroll 2 Stage
M#ZPS30k4E-TF5-130
S#11AG38D4N
410A

Unit is new and was just set a few months ago. Checked Prodigy control and find 2 Low pressure switch faults, and the third had locked it out. Reset system, and checked operation. System runs perfectly in 1st stage cooling. Pressures are great, Comp, fan and blower amps all within range and at proper speed. Everything is running according to design.

2nd Stage Cooling kicks in. Blower and fan ramp up, amp draws are still doing great, and Suction just drops off the radar. Discharge Pressure remains constant and acts normal. Suction drops to 70psi.

This is a single circuit system. Every component is used in 1st stage as 2nd stage. Only component that changes is the compressor. I am thinking the bypass ports are not closing and the compressor remains at 67% capacity. With the increased blower speed suction is falling off. I have never seen this before, so any input you guys have is appreciated.

OAT 78'
SAT 66
RAT 78'

1st stage
Pressures 125-325
Comp 4.7A
Fan .9A
Blower .76A
Superheat 18'
Subcooling 12'

2nd Stage
Pressures 70-325
Comp 6.42A
Fan 1.1A
Blower 1.8
Superheat 54'
Subcooling 13'

One thing i did not do was remove charge, and recharge to factory specs. I recommended that we rule that out before we condemn anything. I see no signs of oil anywhere, and I checked pressures according to unit chart and everything is up too par. I truly don't believe this is a charge issue.

http://www.youtube.com/watch?v=uPhthHuZsQk