Specifications

ManualsBrandsMcQuay ManualsAir ConditionerMWMV

Unit Operation – General

Mark IV/AC-Control Units

Note: At start-up of unit, ensure that temperature, ow rate

and voltage are within specied limits required for

proper unit operation. Each unit has its own control

or remote control, utilizing an internal thermostat (unit

mounted) and touch-pad selector switch or a wall

mounted thermostat (remote control units).

Each unit has a Mark IV/AC version printed circuit board.

Its control is available in unit mounted or remote wall

thermostat. The Mark IV/AC controller has a 14-pin low

voltage terminal strip for a hardwired interface for all

the necessary eld connections interfacing to external

equipment (see Table 8). The low voltage output from

the low voltage terminal strip is always 24 volts AC.

Terminals F and V on the low voltage terminal strip

supply 24 volts DC-power.

Table 8: 14-Position Terminal Strip

Pin Designation Description

1 C Transformer ground (0vac)

2 R Transformer supply (24vac)

3 V – DC power connection

4 P Pump request output

5 A Alarm fault output

6 U Unoccupied input

7 L Load shed input

8 E Remote shutdown input

9 F +DC power connection

10 Y1 Occupied cooling mode input

11 W1 Occupied heating mode input

12 G Fan only input

13 W2 Unoccupied heating mode input

14 O Tenant override input

The 24 volt low voltage terminal strip is set up so R-G

or F-G energizes the fan, R-Y1 or F-Y1 energizes

the compressor for cooling operation, R-W1 or F-W1

energizes the compressor and reversing valve for

heating operation. The reversing valve is energized in

the heating mode. The circuit board has a fan interlock

circuit to energize the fan whenever the compressor’s on

if the thermostat logic fails to do so.

Remember the output to the wall stat can be AC current

or DC current. Terminal (R) on the wall stat can be

connected to terminal (R) on the PC board for AC voltage

or to terminal (F) on the PC board for DC voltage.

AC current DC current

R to G = fan only F to G = fan only

R to Y1 = cooling F to Y1 = cooling

R to W1 = heat F to W1 = heat

Continuous Fan: Units are factory wired for continuous

operation. When power is applied and the start switch is

depressed, the fan will run.

Cooling or Heating – Auto Operation: Rotate the

thermostat knob to either warmer or cooler. Select fan

speed. Depress the start button. Unit will start within 0 to

32 seconds.

Lockout Circuit: Each unit has its own lockout circuit

to lock out compressor operation when an abnormal

condition should appear. During unit operation, the

compressor will be automatically turned off due to one

of the two safety openings. High pressure is set at 600

psi (4136 kPa) and low temperature switch is set at 28˚F

(-2˚C). Condensate overow and brownout protection

are also included.

Remote Reset of Automatic Lockouts: The Remote

Reset feature provides the means to remotely reset

automatic lockouts generated by high-pressure and/or

low-temperature (in heating) faults. When the Mark IV

board is in automatic lockout due to one of these faults,

and the cause of the fault condition has been alleviated,

energizing the O-terminal for 10 seconds or more will

force the Mark IV board to clear the lockout. A unit power

cycle can also be used to clear an automatic lockout if

the conditions causing the fault have been alleviated.

Fault Retry To Minimize Nuisance Trips: The Fault

Retry feature helps to minimize nuisance trips of

automatic lockouts caused by high-pressure and/or low-

temperature (in heating) faults. This feature clears faults

the rst two times they occur within a 24-hour period and

triggers an automatic lockout on the 3rd fault. The retry

count is reset to zero every 24 hours.

Cooling or Heating – Manual Operation: Rotate the

thermostat knob to either warmer or cooler. Select fan

speed, depress the heat or cool button, and unit will start

within 0 to 32 seconds.

The Mark IV/AC-circuit board system has built-in

features such as random start, compressor time delay,

night setback, load shed, shutdown, condensate

overow protection, defrost cycle, brownout, and LED/

fault outputs. Table 9 shows the LED and fault output

sequences. The 24 volt low voltage terminal strip is set

so R-G energizes the fan. R-W1 energizes the fan and

compressor and reversing valve for heating operation.

The reversing valve is set up to be energized in the

heating mode. The circuit board has a fan interlock circuit

to energize the fan whenever the compressor is on.