IM 422-4 / Page 11 (Rev. 5/99)
An inherent advantage of the Incremental system is that
failure of any one part affects only one Incremental condi-
tioner 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 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 replace-
ment of a defective part is possible. The defective part can
then be returned to McQuay or one of its authorized service
stations. So long as it is still in warranty, it is repaired or
replaced and returned to the owner without cost for shop labor
and material. Thus, the stock of replacement parts is con-
stantly replenished. To the right is listed the kind of parts
which McQuay recommends be carried in stock, together with
the quantity of parts recommended per 100 Incremental
conditioners installed.
Recommended Spare Parts
Qty. Per
Part Name
100 Units
Cooling Chassis . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 1
Compressor Overload Device . . . . . . . . . . . . . . . . . . 1
Compressor Running Capacitor . . . . . . . . . . . . . . . . . 1
Evaporator Fan Motor . . . . . . . . . . . . . . . . . . . . . . . . . 1
Condenser Fan Motor . . . . . . . . . . . . . . . . . . . . . . . . . 1
Pushbutton Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Damper Switch . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Thermostat . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . . 2
Knob for Thermostat . . . . . . . . . . . . . . . . . . . . . . . . . . 6
Control Relay (if used) . . . . . . . . . . . . . . . . . . . . . . . . 1
Damper Motor (if used) . . . . . . . . . . . . . . . . . . . . . . . . 2
Touch-up Paint (1 pt. spray can) . . . . . . . . . . . . . . . . 1
Oil for Fan Motors (gallons) . . . . . . . . . . . . . . . . . . . . 1
For the current spare parts list and applicable prices, see your
McQuay representative or write McQuayService, P.O. Box
1551, Minneapolis, MN 55440.
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 trouble-
shooting mechanic. Figure 18 illustrates the refrigeration
cycle. The diagram shows what occurs in each compo
nent of
Refrigeration Cycle
a hermetically sealed system, as used in all McQuay equip-
ment. The temperatures shown are typical of what they might
be when the air entering the condenser (outdoor tempera-
ture) is 95 F (35 C) and the temperature of the conditioned
space is 75 F to 80 F (24 C to 27 C).
Figure 18. Refrigeration cycle
45 F (7 C) R-22
(Liquid & Gas)
To Evaporator
Capillary
Restrictor
120 F (49 C) Condenser Air
To Outdoors
80 F (27 C) Room Air
To Evaporator
285.3 psia (2059 kPa)
R-22 To Condenser
(Hot Gas)
94 F (35 C) Outdoor Air
To Condenser
60.3 psia (416 kPa) R-22
and 60 F (15.5 C)
To Compressor (Gas)
50 F (15.5 C) Conditioned
Air To Room
Hermetic Compressor
Condenser
Evaporator
110 F (43 C)
Liquid R-22
To Capillary
