McQuay MHC Series, Installation & Maintenance Data, Page: 13 / 36

IM 985-1 / Page 13 of 36
Mechanical (Compressor) Heating Override
to Electric Heat Operation
Note: Only with units equipped with the electric
heat feature
In­ the­ event­ of­ a­ compressor­ failure­ or,­ electric­ heat­ is­
desired­over­mechanical­(compressor)­heating,­a­factory­
certified service technician may reconfigure the male and
female­plugs­to­enable­electric­heat .­This­option­allows­
emergency­electric­heat­when­mechanical­heating­is­not­
available .­Electric­heat­can­be­disabled­and­the­unit­can­be­
returned­to­mechanical­(compresssor)­heating­operation­
when­desired­(Figure­11) .
Note: In electric heat mode, unit will not run
compressor on a call for heating. The electric heater
will be utilized instead.
Before disconnecting or connecting plugs, be sure power
to unit is off and power disconnect switch is in the off position.
Switching Mechanical (Compressor) Heating to
Electric Heat Operation
1 .­ Disconnect­wires­70­and­71­plug­located­on­outside­
of­control­box­from­socket­that­connects­to­the­
Entering­Water­Temperature­(EWT)­Sensor­(Figure­
11) .
2 .­ Reconnect­wires­70­and­71­plug­into­the­Electric­
Heat­(EH)­socket­located­on­the­back­of­the­hinged­
control­box­(Figure­11) .
3 .­ Coil­the­disconnected­Entering­Water­Temperature­
Sensor­wire­and­store­in­safe­location­for­later­use .
Figure 11. Switching to Electric Heat Detail
Table 3. Electric Heater Current and Power
Electrical Data
General
1 .­ Be­sure­the­available­power­is­the­same­voltage­and
­
phase­as­that­shown­on­the­unit­serial­plate .­Line­and
­ voltage­wiring­must­be­done­in­accordance­with­
local­codes­or­the­National­Electrical­Code,­
whichever­is­applicable .
2 .­ Apply­correct­line­voltage­to­the­unit .­A­disconnect
­
switch­near­the­unit­is­required­by­code .­Power­
to­the­unit­must­be­sized­correctly­and­have­dual­
element­(Class­RK5)­fuses­or­HACR­circuit­breaker­
for­branch­circuit­overcurrent­protection .­See­the­
nameplate­for­correct­ratings .
3 .­ All­208-230V­single­phase­units­are­factory­wired­
for 208 volt operation unless specified for 230 volts.
Operating Voltages
115/60/1 . . . . . . . . 104 volts min.; 127 volts max.
208-230/60/1 . . . . 197 volts min.; 253 volts max.
265/60/1 . . . . . . . . 238 volts min.; 292 volts max.
230/50/1 . . . . . . . . 197 volts min.; 253 volts max.
Note: Voltages listed are to show voltage range.
However, units operating with over voltage and under
voltage for extended periods of time will experience
premature component failure.
Operating Limits
Environment
This­equipment­is­designed­for­indoor­installation­
only. ­Sheltered­locations­such­as­attics,­garages,­
etc., generally will not provide sufficient protection
against­extremes­in­temperature­and/or­humidity,­and­
equipment­performance,­reliability,­and­service­life­may­
be­adversely­affected .
Sizes 007, 009, 012 Sizes 015, 018
Nominal Voltage 2.5kW 3.5kW
Power (kW) Current (Avg) Power (kW) Current (Avg)
208
2.01 9.67 2.71 13.02
230
2.46 10.70 3.31 14.40
240
2.68 11.16 3.61 15.03
265
3.27 12.33 4.40 16.59
277
3.57 12.88 4.80 17.35
WARNING