IM 950-1 / Page 33 of 38
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 41
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 41. Refrigeration Cycle
Maintenance
95°F. (35°C.)
Outdoor Air to Condenser
60.3 psia (416 kPa)
& 60°F. (15.5C.)
to Compressor (Gas)
Hermetic
Compressor
60°F. (15.5°C.)
Conditioned Air to Room
80°F. (27°C.)
Room Air to Evaporator
45°F. (7°C.)
R22 (Liquid and Gas)
to Evaporator
120°F. (49°C.) Condenser Air
to Outdoors
110°F. (43°C.)
Liquid R22 to
Capillary
Capillary
Restrictor
Condenser
285.3 psia (1967.7 kPa) R22 to Condenser (Hot5 Gas)
Evaporator
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
..........................................................
2
Compressor Overload Device
.....................................
2
Compressor Running Capacitor
..................................
2
Fan Motor. Capacitor
..................................................
2
Control Board
..............................................................
2
Thermostat
..................................................................
2
Control Relay (if used)
................................................
2
Damper Motor (if auto damper)
..................................
2
Electric Resistance Heater (if electric heat)
...............
2
Touch-up Paint (1 pt. spray can)
.................................
2
For the current spare parts list, and applicable
prices, see your McQuay representative or write
McQuay Service, P.O. Box 1551, Minneapolis, MN
55440.
