Operating instructions

IMM AGSB-60 59
NOTE: Exceeding normal charge can result in abnormally high discharge pressure and relief
valve discharge, or cause low discharge superheat resulting in oil loss into the system.
An element inside the sight glass indicates the moisture condition corresponding to a given
element color. The color code is printed on the edge of the sight glass. If the sight glass does
not indicate a dry condition after about 12 hours of operation, the circuit should be pumped
down and the filter-drier changed. An oil acid test is also recommended.
Evaporator Sight Glass
There are evaporator sight glasses on the side of the evaporator barrel, 1 for each circuit,
located approximately half way up the vessel. The evaporator sight glasses are for reference
use only. The electronic expansion valve control algorithms vary with operating conditions
and will cause a higher or lower liquid level in the evaporator. You can use the sight glasses to
give you some relative decision making information. If there is a considerable amount of oil
out in the system, you may see oil floating on the evaporator liquid level, the refrigerant may
have a yellowish tint or you may see an oil film on the sight glass as the liquid level rises and
falls. Oil in the evaporator is often an indication of too much oil in the circuit, or the circuit is
running low discharge superheat. Oil will also increase the evaporator approach value above
normal. For refrigerant charge while in subcooling control, typically half of a sight glass full
is normal. A full sight glass with low discharge superheat. is a good indication of too much
refrigerant charge. An empty sight glass, with low pressure unload and trip events, is a good
indication of insufficient refrigerant charge.
Lead-Lag
A feature on all McQuay AGS air-cooled chillers is a system for alternating the sequence in
which the compressors start to balance the number of starts and run hours. Lead-Lag of the
refrigerant circuits is accomplished automatically through the MicroTech II controller. When
in the auto mode, the circuit with the fewest number of starts will be started first. If all circuits
are operating and a stage off in the number of operating compressors is required, the circuit
with the most operating hours will cycle off first. The operator can override the MicroTech II
controller, and manually select the lead circuit as circuit #1, #2, or #3.