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Maintenance
Recommended Spare Parts
An inherent advantage of the Incremental system is
that failure of any part affects only one incremental
conditioner and does not interrupt the operation of the
rest of the system. A further advantage is that a failed
part can be quickly and easily replaced, thus minimizing
the inoperative time of the equipment. This is so,
however, only if a replacement part is quickly available.
In order to replace a failed part quickly and keep all
incremental conditioners in good operating condition,
McQuay International recommends that at the time
incremental conditioners are purchased, owners arrange
for a small stock of replacement parts.
Where an owner carries such a stock, immediate
replacement of defective parts is possible. The defective
part can then be returned to McQuay warranty parts. As
long as it is still in warranty, it is repaired or replaced
and returned to the owner with out cost for shop labor
and material. Thus, the stock of replacement parts is
constantly replenished. Below is a list of the kinds
of parts which McQuay International recommends to
be carried in stock together with the quantity of parts
recommended per 100 incremental conditioners installed.
Cooling Chassis .......................................................... 1
Compressor Overload Device ..................................... 1
Compressor Running Capacitor .................................. 1
Evaporator Fan Motor ................................................. 1
Condenser Fan Motor ................................................. 1
Damper Switch ............................................................ 2
Thermostat .................................................................. 2
Control Relay (if used) ................................................ 1
Damper Motor (if used) .............................................. 2
Touch-up Paint (1 pt. spray can) ................................. 1
For the current spare parts list, and applicable prices, see
your McQuay representative or write McQuay Service,
P.O. Box 1551, Minneapolis, MN 55440.
Refrigeration Cycle
Every motor-driven refrigeration system operates on
the carnot cycle. A practical understanding of what goes
on at the various steps in this cycle can be a big help
to the troubleshooting mechanic. Figure 31 illustrates
the refrigeration cycle. The diagram shows what occurs
in each component of a hermetically sealed system
as used in all McQuay Air Conditioning equipment.
The temperatures shown are typical of what they
might be when the air entering the condenser (outdoor
temperature) is 95°F, (350 C) and the temperature of the
conditioned space is 80°F (270 C).
Figure 31. Refrigeration Cycle
45°F. (7°C.)
R22 (Liquid and Gas)
to Evaporator
80°F. (27°C.)
Room Air to Evaporator
Capillary
Restrictor
110°F. (43°C.)
Liquid R22 to
Capillary
Evaporator
60.3 psia (416 kPa)
to Compressor (Gas)
60°F. (15.5°C.)
Conditioned Air to Room
120°F. (49°C.) Condenser Air
to Outdoors
Condenser
95°F. (35°C.)
Outdoor Air to Condenser
& 60°F. (15.5C.)
Hermetic
Compressor
IM 882 / Page 33 of 36
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