Trane 18-BC55D1-2 NstaIers Guide, Electrical Connections, Defrost Control, Compressor Start UP

nstaIer's Guide

10.Replace liquid service pressure tap port cap and valve

stem cap. These caps MUST BE REPLACED to prevent leaks. Replace valve stem and pressure tap cap

finger tight, then tighten an additional 1/6 turn.

11.The gas valve can now be opened. Open the gas valve by removing the shut-off valve cap and turning the valve

stem 1/4 turn counterclockwise, using 1/4" Open End or Adjustable wrench. See Figure 4.

12.The gas valve is now open for refrigerant flow. Replace valve stem cap to prevent leaks. Again, these caps

MUST BE REPLACED to prevent leaks. Replace valve stem and pressure tap cap finger tight, then tighten an

additional 1/6 turn. See Figure 4.

If refrigerant lines are longer than 15 f_et and/or a difi_rent

size than recommended, it will be necessary to adjust system

refrigerant charge upon completion of installation. See unit Service Facts.

E. ELECTRICAL CONNECTIONS

When installing or servicing this equipment, ALWAYS exercise basic safety precautions to avoid the possibility of electric shock.

1.Power -wiring and grounding of equipment must comply with local codes.

2.Power supply must agree with equipment nameplate.

3.Install a separate disconnect switch at the outdoor unit.

4.Ground the outdoor unit per local code requirements.

5.Provide flexible electrical conduit whenever vibration

transmission may create a noise problem within the structure.

6.The use of color coded low voltage wire is recommended to simplify connections between the outdoor unit, the

thermostat and the indoor unit.

Table 1 --NEC Class II Control Wiring

	24 VOLTS
WIRE SIZE	MAX. WIRE	LENGTH
18 AWG	150 FT
16 AWG	225	FT.
14 AWG	300	FT.

7.Table i defines maximum total length of low voltage wiring from outdoor unit, to indoor unit, and to thermostat.

8.Mount the indoor thermostat in accordance with instruc-

tion included with the thermostat. Wire per appropriate hook-up diagram (included in these instructions).

F.DEFROST CONTROL

The demand defrost control measures heat pump outdoor

ambient temperature -with a sensor located outside the outdoor coil. A second sensor located on the outdoor coil is

used to measure the coil temperature. The difference between

the ambient and the colder coil temperature is the difference

or delta-T measurement. This delta-T measurement is

representative of the operating state and relative capacity of

the heat pump system. By measuring the change in delta-T,

we can determine the need for defrost. The coil sensor also

serves to sense outdoor coil temperature for termination of the defrost cycle.

FAULT IDENTIFICATION

A fault condition is indicated by the flashing light on the defrost control inside the heat pump control box.

In normal operation, the defrost control light will flash once each second. If the light is flashing more than once per second or not at all, refer to the service manual for that unit.

PIN IDENTIFICATION (See Figure 5.)

1.TEST COMMON (Shorting any of the other pins to this pin causes the function of the other pin to be executed. Leaving this pin open results in the normal mode of operation.)

2.TST = Test (Shorting TEST_COMMON to this pin speeds up all defrost board timings.)

3.FRC_DFT = Forced Defrost (Short TEST_COMMON to this pin for two (2) seconds to initiate a forced defrost. Remove the short after defrost initiates.)

4.LOW_FAN = Low speed Fan test mode (Short

TEST_COMMON to this pin to force the outdoor fan to low speed. When the short is removed, the fan will go

to high speed for approximately 15 seconds and then

return to the speed it was running before the short was applied.)

DEFROST CONTROL CHECKOUT

Normal operation requires:

a. LED on board flashing 1 time/second.

b.24V AC between R & B

c. 24V AC between Y & B with unit operating

d. Defrost initiation when FRC DFT pin is shorted to

TEST_COMMON pin.

If a defrost control problem is suspected, refer to the service

information in control box.

Do NOT connect 24 VAC to T1 (ODS-A) terminal. ODS-A thermistor WiLL BE BLOWN.

G. COMPRESSOR START UP

After all electrical wiring is complete, SET THE THERMO-

STAT SYSTEM SWITCH IN THE OFF POSITION SO

COMPRESSOR WILL NOT RUN, and apply power by closing the system main disconnect switch. This will activate the compressor sump heat (where used). Do not change the

Thermostat System Switch until power has been applied for one (1) hour. Following this procedure -will prevent potential compressor overload trip at the initial start-up.

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4 18-BC55D 1-2