Unit installation

OMRCPMICRO 63

these items should be adjusted accordingly. Ice jobs are considered to be jobs in which the leaving

chilled water set point is 34°F or less. Refer to the Reset Options section for information on ice job set

points.

2. Check the Leaving Evaporator Set Points for the "ControlBand", the "StartUpD-T" (Start-up Delta-T) and

the ShutDn D-T" (Shut Down Delta-T) on Menu 14. A good rule of thumb for the Control Band setting is

to use the formula:

UnitStages

TEvaporator

trolBandTypicalCon °+= 5.0

The Start Up Delta-T and the Shut Down Delta-T define when the unit will start from an off condition and

shut completely down. The Start Up Delta-T can be raised to ensure the unit doesn't turn on too soon.

The Shut Down Delta-T can be decreased so that the unit shuts off before the leaving water temperature

gets too low. Refer to Normal Sequence of Operation and the Menu Description sections of this manual

for further information on these set points.

3. Check the actual water flow rate through the unit; are the pumps running continuously, are the pumps

shut off at night, is there a variable water flow situation, is there adequate water mass in the chilled water

system, is the water loop too short? McQuay reciprocating chillers and Templifiers require a constant

adequate flow of water through the evaporator. Refer to the unit installation and maintenance manual for

water and glycol flow charts. When short water loops are present, the chilled water is pulled down

quickly. A good rule of thumb is that the water temperature should be pulled down no more than 1°F

every 15 to 20 minutes— a 20-minute water loop. Inadequate water mass in the chilled water system has

the same effect. Refer to McQuay literature regarding applications.

4. Investigate physical considerations in the refrigerant circuit. This is especially important when only one

circuit is consistently tripping on the "Freeze Stat Prot" alarm and the other is not. The alarm, head

pressure and leaving evaporator set points are used for both circuits so the only difference between the

two circuits would be physical. Check the operation of the expansion valve (TXV). Check the sight glass

and take a sample of the refrigerant to check for moisture. Visually inspect and leak test the machine. The

unit could be low on charge, causing low suction pressure. Check to make sure the superheat and/or low

subcooling are within acceptable guidelines. High superheat and/or subcooling can cause low suction

pressure. Check the evaporator pressure transducer for correct operation. Refer to the Erroneous Pressure

Readings troubleshooting section.

5. Verify that the Head Pressure Set Points on Menu 17 are suitable for the particular job. Adjustment of the

"MinLift-35%", the "MinLift-100%" and/or the "DeadBandMult" set points may be necessary. Refer to

the Head Pressure Control section of this manual for head pressure adjustment guidance.

Output board

Solid-state relays on the MicroTech Controller Output Board all have contacts open when de-energized.

However, because these relays are "solid-state", the contacts are not "open" in the sense that

electromechanical relays open their contacts. Instead, the relay switches from low to high resistance.

When checking the voltage in a circuit where these relays have been incorporated, it is possible to be

confused by the presence of voltage on the load side of the relay. If there is a load on the relay, the circuit will

behave like a traditional relay circuit. That is, if the relay switches to "off' the voltage will drop to zero at the

output of the relay. But, should the circuit be "open" between the relay output and the load, and the output

relay is "off", the high resistance of the relay and the voltmeter form a series circuit. A digital voltmeter will

not indicate any decrease in voltage and an analog voltmeter will typically indicate a minor decrease in voltage

when the relay turns "off".