Carrier 48VT(N) Pre-Start-Up, Transformer Protection, Balance Point Setting-Thermidistator Hybrid

more than 100 ft (30.5 m) from the unit (as measured along the control voltage wires), use no. 16 AWG color-coded, insulated (35_C minimum) wires.

Locate the seven (eight on 3-phase) low voltage thermostat leads in 24 volt splice box. See Fig. 10 for connection diagram. Run the low-voltage leads from the thermostat, through the control wiring inlet hole grommet (Fig. 2 and 3), and into the low-voltage splice box. Provide a drip loop before running wires through panel. Secure and strain relief all wires so that they do not interfere with operation of unit. A gray wire is standard on 3-phase unit for connection to an economizer.

3.Comfort Balance Temperature: When the heat pump is operating below this point, the indoor supply air feels uncomfortable (i.e. too cool). This is purely subjective and will depend on the homeowner’s idea of comfort. Below this temperature the gas furnace should operate in order to satisfy the desire for indoor comfort.

Transformer Protection

The transformer is of the energy-limiting type. It is set to withstand a 30-sec. overload or shorted secondary condition. If an overload or short is present, correct overload condition and check for blown fuse on gas control board or Interface Fan Board. Replace fuse as required with correct size and rating.

A

HIGH VOLTAGE POWER LEADS (SEE UNIT WIRING LABEL)

EQUIP GR

CONTROL BOX

POWER

SUPPLY

FIELD-SUPPLIED FUSED DISCONNECT

PRE-START-UP

!WARNING

FIRE, EXPLOSION, ELECTRICAL SHOCK HAZARD

Failure to follow this warning could result in personal injury, death or property damage.

48VT--

LOW-VOLTAGE POWER LEADS (SEE UNIT WIRING LABEL)

SPLICE BOX

WHT(W1)	W
YEL(Y)	Y
GRN(G)	G
RED(R)	R
BRN(C)	C
ORN(O)	O
BLU (DH)	DH
GRA (Y2)	3-Phase
	Only

THERMOSTAT (TYPICAL)

1.	Follow recognized safety practices and wear protective
	goggles when checking or servicing refrigerant system.
2.	Do not operate compressor or provide any electric power
	to unit unless compressor terminal cover is in place and
	secured.
3.	Do not remove compressor terminal cover until all
	electrical sources are disconnected and tagged.
4.	Relieve and recover all refrigerant from system before
	touching or disturbing anything inside terminal box if
	refrigerant leak is suspected around compressor
	terminals.

A09067

Fig. 10 - High and Control-Voltage Connections

Balance Point Setting-Thermidistat or Hybrid

Thermostat

BALANCE POINT TEMPERATURE-The “balance point” temperature is a setting which affects the operation of the heating mode. This is a field-selected input temperature (range 5 to 55_F) (-15 to 12_C) where the Thermidistat or dual fuel thermostat will monitor outdoor air temperature and decide whether to enable or disable the heat pump. If the outdoor temperature is above the “balance point”, the heat pump will energize first to try to satisfy the indoor temperature demand. If the heat pump does not make a sufficient improvement within a reasonable time period (i.e. 15 minutes), then the gas furnace will come on to satisfy the indoor temperature demand. If the outdoor temperature is below the “balance point”, the heat pump will not be allowed to operate (i.e. locked out), and the gas furnace will be used to satisfy the indoor temperature. There are three separate concepts which are related to selecting the final “balance point” temperature. Read each of the following carefully to determine the best “balance point” in a hybrid installation:

1.Capacity Balance Temperature: This is a point where the heat pump cannot provide sufficient capacity to keep up with the indoor temperature demand because of declining outdoor temperature. At or below this point, the furnace is needed to maintain proper indoor temperature.

2.Economic Balance Temperature: Above this point, the heat pump is the most cost efficient to operate, and below this point the furnace is the most cost efficient to operate. This can be somewhat complicated to determine and it involves knowing the cost of gas and electricity, as well as the efficiency of the furnace and heat pump. For the most economical operation, the heat pump should operate above this temperature (assuming it has sufficient capacity) and the furnace should operate below this temperature.

5. Never attempt to repair soldered connection while

refrigerant system is under pressure.

6. Do not use torch to remove any component. System

contains oil and refrigerant under pressure.

To remove a component, wear protective goggles and

proceed as follows:

a. Shut off electrical power to unit and install lockout

tag.

b. Relieve and reclaim all refrigerant from system

using both high- and low-pressure ports.

c. Cut component connecting tubing with tubing

cutter and remove component from unit.

d. Carefully unsweat remaining tubing stubs when

necessary. Oil can ignite when exposed to torch

flame.

Proceed as follows to inspect and prepare the unit for initial start-up:

1.Remove access panels (see Fig. 19).

2.Read and follow instructions on all WARNING, CAUTION, and INFORMATION labels attached to, or shipped with, unit.

3.Make the following inspections:

a.Inspect for shipping and handling damages such as broken lines, loose parts, disconnected wires, etc.

b.Inspect for oil at all refrigerant tubing connections and on unit base. Detecting oil generally indicates a refrigerant leak.

c.Leak test all refrigerant tubing connections using electronic leak detector, halide torch, or liquid-soap solution. If a refrigerant leak is detected, see the Check for Refrigerant Leaks section.

d.Inspect all field- and factory-wiring connections. Be sure that connections are completed and tight.

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