Carrier 38AD034 - Control Circuit Protection and Winter Start; Control Circuit Reset Procedures; Compressor Motor Overheating Protection; Winter Start Control Implementation

38AB084 UNIT
Timers in this unit provide basic function, plus
40 sec bypass for oil failure switch and 1 sec delay
to accomplish part-winding start.
For specific sequence for each unit, refer to
Timing Charts in Fig. 14.
PRESSURE
DIFFERENTIAL
ADJUSTMENT
SCREW
BYPASS
PISTON
CONTROL
SET POINT
ADJUSTMENT
NUT
VALVE BODY
DIFFERENTIAL SCREW'
SEALING CAP
(CAP MUST BE REPLACED
TO PREVENT REFRIGERANT LEAKAGE)
Fig. 13 — Capacity Control Valve
o
38AB054 THRU 064 UNITS
H--40SEC '-5
NOTE BLACK INDICATES CLOSED CONTACTS
38AB084 UNITS
Fig. 14 — Timing Charts
Control Circuit Reset
38AD024 THRU 044 AND 38AB084 - Control
circuit locks out on these units in the event of oil
pressure loss, excessive motor temperatures, or
excessive discharge temperatures Reset is
accomplished by pushing reset button(s) in unit
control box.
38AB054 AND 064 - Loss of oil pressure or
excessive motor temperatures cause control circuit
lock out on these units Reset is accomplished by
pushing reset button on oil failure safety
switch(es). All other safety controls on each unit
are automatic reset, with restart accomplished
through unit timers.
Oil Pressure Safety Control (OPS) for each com¬
pressor will stop unit if oil pressure differential is
not established or maintained at either compressor.
If OPS stops unit, determine and correct the
cause (such as loss of compressor oil or flooded
compressor) before restarting unit. Failure to do so
will constitute abuse. Equipment failure due to
abuse is not covered by the Warranty To restart
unit, push manual reset button in unit control box
(except 38AB054 and 064 units). Reset button is
on OPS on 38AB054 and 064.
Compressor Motor Protection on 38AD024 thru
044 and 38AB084 consists of three temperature
sensors (one for each phase) embedded in the
motor windings, and solid state modules in unit
control box.
Sensors are part of a temperature bridge. If a
motor winding overheats, the bridge circuit will
unbalance and a silicone-controlled rectifier in the
module will de-energize a relay which opens a set
of normally open contacts in the module and stops
the compressor.
If one sensor fails, it can be jumped with a
75-ohm, 2-watt resistor. When checking or testing
module, do not apply more than 6 volts across
sensor terminals. Many test instruments exceed this
voltage rating; check before using.
If a component in a module fails on 38AD024
thru 044, the entire module must be replaced. On
38AB084, the transformer is external to the
module and may be replaced separately. Replace
transformer with a Carrier specified balanced
transformer.
To restart compressor after shutdown due to
motor protection trip, push control circuit reset
button in unit control box.
Safety Relief - All 38AB,AD units are protected
against excessive pressure by a fusible plug inserted
in the liquid line.
-> Winter Start Control — On 38AB units (not
necessary on 38AD units because the timer
supplies this function), install a liquid line pressure-
stat (Carrier part no. HK02AB026) and evaporator
freeze-up protector (defrost thermostat. Carrier
part no. HH22UA025).
38AD control circuits incorporate a 150 sec¬
onds timed bypass of the low-pressure switch to
in