30
Refrigerant Charging
NOTE: Do not vent or depressurize unit refrigerant to atmo-
sphere. Remove and recover refrigerant following accepted
practices.
Air Coil Fan Motor Removal
Disconnect motor power wires from motor terminals before
motor is removed from unit.
1. Shut off unit main power supply.
2. Loosen bolts on mounting bracket so that fan belt can be
removed.
3. Loosen and remove the 2 motor mounting bracket bolts
on left side of bracket.
Slide motor/bracket assembly to extreme right and lift out
through space between fan scroll and side frame. Rest motor on
a high platform such as a step ladder. Do not allow motor to
hang by its power wires.
TROUBLESHOOTING
When troubleshooting problems with a WSHP, consider the
following:
Thermistor —
A thermistor may be required for single-
phase units where starting the unit is a problem due to low
voltage. See Fig. 24 for thermistor nominal resistance.
Control Sensors —
The control system employs 2 nom-
inal 10,000 ohm thermistors (FP1 and FP2) that are used for
freeze protection. Be sure FP1 is located in the discharge fluid
and FP2 is located in the air discharge. See Fig. 25.
Thermostatic Expansion Valves —
Thermostat-
ic expansion valves (TXV) are used as a means of metering the
refrigerant through the evaporator to achieve a preset superheat
at the TXV sensing bulb. Correct superheat of the refrigerant is
important for the most efficient operation of the unit and for the
life of the compressor.
Packaged heat pumps typically use one bi-flow TXV to me-
ter refrigerant in both modes of operation. When diagnosing
possible TXV problems it may be helpful to reverse the refrig-
erant flow to assist with the diagnosis.
Geothermal and water source heat pumps are designed to
operate through a wide range of entering-water temperatures
that will have a direct effect on the unit refrigerant oper-
ating pressures. Therefore, diagnosing TXV problems can be
difficult.
TXV FAILURE — The most common failure mode of a TXV
is when the valve fails while closed. Typically, a TXV uses
spring pressure to close the valve and an opposing pressure,
usually from a diaphragm, to open the valve. The amount of
pressure exerted by the diaphragm will vary, depending on the
pressure inside of the sensing bulb. As the temperature of and
pressure within the bulb decreases, the valve will modulate
closed and restrict the refrigerant flow through the valve. The
result is less refrigerant in the evaporator and an increase in the
superheat. As the temperature at the bulb increases the dia-
phragm pressure will increase, which opens the valve and
allows more refrigerant flow and a reduction in the superheat.
If the sensing bulb, connecting capillary, or diaphragm
assembly are damaged, pressure is lost and the spring will force
the valve to a closed position. Often, the TXV will not close
completely so some refrigerant flow will remain, even if inade-
quate flow for the heat pump to operate.
The TXV sensing bulb must be properly located, secured,
and insulated as it will attempt to control the temperature of the
line to which it is connected. The sensing bulb must be located
on a dedicated suction line close to the compressor. On a pack-
aged heat pump, the bulb may be located almost any place on
the tube running from the compressor suction inlet to the
reversing valve. If the bulb is located on a horizontal section, it
should be placed in the 10:00 or 2:00 position for optimal
performance.
The bulb must be secured to the pipe using a copper strap.
The use of heat transfer paste between the bulb and the pipe
will also help ensure optimum performance.
The bulb must also be properly insulated to eliminate any
influence on valve operation by the surrounding conditions.
Cork tape is the recommended insulation as it can be molded
tight to the bulb to prevent air infiltration.
WARNING
To prevent personal injury, wear safety glasses and gloves
when handling refrigerant. Do not overcharge system —
this can cause compressor flooding.
CAUTION
Before attempting to remove fan motors or motor mounts,
place a piece of plywood over evaporator coils to prevent
coil damage.
0.0
10.0
20.0
30.0
40.0
50.0
60.0
70.0
80.0
90.0
0.0
20.0
40.0
60.0
80.0
100.0
120.0
140.0
Temperature (degF)
Resistance (kOhm)
Fig. 24 — Thermistor Nominal Resistance
CAUTION
Use caution when tightening the strap. The strap must be
tight enough to hold the bulb securely but caution must be
taken not to over-tighten the strap, which could dent, bend,
collapse or otherwise damage the bulb.
