Troubleshooting Guide -
Tranquility
®
Digital (DXM2) Packaged Units
Rev.: 01/15/14
46
Geothermal Heat Pump Systems
Definitions of Conditions
CONTACTOR OPEN - NOT BUZZING
When the contactor is open but not buzzing, it is an indication
of no voltage to its coil, or that there is voltage to its coil but
the coil is open circulated. If unit does not start, check volt-
age at coil with volt meter. If there is voltage, the coil is open
circulated. Replace the contactor. If no voltage, check power
to control circuit.
LOW SUCTION PRESSURE
If low suction pressure is suspected, switch to heating mode
and check the suction pressure. This suction pressure should
not be lower than the refrigerant pressure equivalent to enter-
ing water temperature minus 40°F, provided there is ad-
equate water fl ow and entering air is approximately at 70°F.
OPEN HIGH PRESSURE SWITCH
It is factory set to shut down the unit at 600 PSI.
EXCESSIVE DISCHARGE PRESSURE
If excessive discharge pressure is suspected, switch to heat-
ing mode and check the discharge pressure. This discharge
pressure should not be higher than the refrigerant pressure
equivalent to entering air dry bulb temperature plus 60°F, pro-
vided there is proper air flow and entering water temperature
is approximately at 70°F.
COMPRESSOR OVERLOADS OPEN AND CLOSE
The purpose of overloads is to quickly sense excessive
compressor current and/or temperature and open the power
circuit to prevent burnout of motor. This condition may be
caused by repeated call to start before pressures equalize,
low voltage, tightness of new compressor, excessive current
draw or the temperature of the suction gas being too warm
to adequately cool the motor. Warm suction gas may be due
to an under charge, too much superheat, restriction in liquid
or suction line, or restriction in capillary. When the overload
opens, it may take from 5 to 30 minutes for it to cool suffi -
ciently to close.
CONTACTOR OPEN - BUZZING
When the contactor is open but buzzing, it is an indication
that its coil is energized but the contactor is unable to close.
NORMAL VOLTAGE TO COIL
Check voltage to coil. It should not be lower than 10% below
rated voltage as the contractor tries to close. If voltage is
normal, the mechanism may be tight or fouled. Remove
and inspect mechanism. Clean if necessary. If too sluggish,
replace contactor.
BELOW NORMAL VOLTAGE TO COIL
Check voltage to coil. If it is lower than 10% below rated volt-
age, it is probably due to low supply voltage, faulty trans-
former or phase loss.
OPEN OVERLOAD SWITCH
Sometimes overloads will fail with contacts in the open posi-
tion, or contacts may be closed but not conducting electri-
cally. To check this, disconnect power circuit. If unit starts,
replace overload if it is located in the electrical box. If unit
does not start, the trouble is elsewhere.
BURNED CONTACTS
Sometimes contacts will close mechanically but will not con-
duct electrically. To check for this, disconnect power circuit
and measure contact resistance with ohmmeter. The meter
should read zero ohms. If meter does not read zero ohms,
replace contactor. If ohmmeter is not available, disconnect
power circuit, place temporary jumpers from line side of con-
tacts and close power circuit. If unit starts, replace contactor.
If unit does not start, trouble is elsewhere. Burned contacts
may also cause high current draw.
EXPANSION VALVE BULB LOST CHARGE
If the bulb of the expansion valve loses its charge,
there will be no pressure to open the valve, thus
causing low suction pressure. To check this,
remove expansion valve bulb from suction line and hold it in
your hand. If the suction pressure does not increase in a few
minutes and there are no restrictions in the refrigerant circuit,
it is an indication that the bulb has lost its charge. Replace
expansion valve.
DISTRIBUTOR TUBE RESTRICTED
To check this, check suction pressure (very low suction
pressure is an indication of restriction or excessive under
charge) on cooling cycle temporarily cut off air to air coil and
allow unit to operate. If there is a partial restriction or exces-
sive undercharge, frost will occur at that point. If there is no
restriction, the evaporator coil will frost uniformly. If there is
a total restriction anywhere in the refrigerant circuit from the
condenser through the evaporator and back to the com-
pressor, there will be no frost, the suction pressure may go
into vacuum and the discharge pressure will correspond to
approximately ambient temperature because there will be no
vapor to compress.
EXCESSIVE SUPERHEAT
Superheat is the temperature of the refrigerant vapor above
the temperature corresponding to the vapor pressure. It
should be 3° to 25°F. Excessive superheat is an indication
that the evaporator is “starved”. That is, not enough liquid
refrigerant in the coil. Excessive superheat may be due to
undercharge, restriction in refrigerant circuit, low discharge
pressure, expansion valve bulb lost charge, too much load on
evaporator, or refrigerant flashing ahead of expansion valve
or capillary due to pressure drop.
HIGH AMPS
Refer to nameplate on unit. Amps should not exceed rating
more than 10%.
POOR EXPANSION VALVE BULB
INSTALLATION
The expansion valve bulb should be securely
mounted and properly located on clean pipe, paral-
lel to pipe with fi rm metal contact and wrapped with insulation
tape to assure proper sensing of suction line temperature.
A-Y
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