Carrier 38AC - Manual (Page 3)

NOTE: Do not depend on sight glass when
charging unit. Use the charging chart.
■
3. Allow system to operate for about 20 minutes.
Take temperature and pressure readings and
check values with the charging chart.
After Charging System, allow unit to run for about
20 minutes. Stop unit and check compressor oil
level. Add oil only if necessary to bring oil into
view in sight glass. If oil is added, run unit for
additional 10 minutes. Stop unit and check oil
level. If level is again low, add oil only after
determining that piping system is designed for
proper oil return and that system is not leaking oil.
Check operation of all safety controls. Replace all
service panels. Be sure that control panel door is
closed tightly.
SERVICE
Defrost Control, consisting of a defrost timer and a
defrost thermostat, interrupts normal system
heating operation if enough frost forms on outdoor
coil to impair overall unit performance. Defrost
control simultaneously stops outdoor fans and
de-energizes reversing valve solenoid to return
system to cooling cycle (outdoor unit as con­
denser; indoor unit as evaporator). Defrost cycle is
90 minutes for 38AC012 and 60 minutes for
38AC016.
For the heat pump to defrost, two conditions
are necessary:
1. Defrost timer contacts must be closed.
2. Refrigerant temperature from outdoor unit
must be cold enough (43± 3 F) to cause defrost
thermostat contacts to close.
Liquid Line Low-Pressure Control (LLP) is con­
nected in liquid line to work with compressor
internal thermostat and discharge thermostat to
provide loss-of-charge protection during the heating
cycle. Control is mounted in control box.
With a high side leak, pressure gradually
decreases until low pressure control stops the
compressor.
With a low side leak there will always be some
pressure in the liquid line. However, compressor
motor temperature will increase because of in­
sufficient suction gas cooling. This causes internal
thermostat or discharge line thermostat to actuate
and stop compressor. When compressor stops,
system pressure equalizes and contacts on pressure
control open. The compressor cannot restart until
leak is repaired and system recharged.
Low-Pressure Control (LP) is a single-pole switch
connected into the refrigerant system at com­
pressor suction connection and into 24-volt control
circuit. Control provides loss-of-charge protection
and freeze-up protection during cooling cycle and
is inoperative during heating cycle. See Table 1 for
pressure settings.
Head Pressure Control (Fan-Cycling Thermostat) —
A feeler bulb in the outdoor coil inlet airstream
senses temperature of air entering coil to control
no. 2 fan on 38AC012 and no. 2 and 3 fans on
38AC016. Open and close temperatures are shown
in Table 1.
Accessory Motormaster^M head pressure con­
trol for no. 1 fan (if used) allows operation at
lower ambients.
See accessory instructions.
Time Guard Circuit for compressor causes a
5-minute delay before restarting compressor after
shutdown for any reason. On starting, the Time
Guard Timer causes a delay of 15 seconds after
thermostat closes before compressor will start. On
compressor shutdown, the timer recycles for 4
minutes 45 seconds. During this time the com­
pressor cannot restart.
Safety Relief — A rupture disc in the accumulator
and a relief valve in the compressor provides
pressure relief under abnormal temperature and
pressure conditions.
Electric Resistance Crankcase Heater is inserted
into the compressor crankcase. It is operated from
the normally closed contacts of the holding relay
and is automatically energized when the com­
pressor stops. This heater keeps crankcase warm to
prevent oil dilution by refrigerant and ensures good
lubrication and minimizes loss of oil during
start-up.
If power to unit has been off for an extended
period of time, energize crankcase heater at least 3
hours prior to starting compressor.
Compressor Section — Remove top and end panel
for access to this section. Additional access to
expansion valve, distributor and coil piping is
available by removing inboard fan, motor-support
panel assembly and coil end baffle between com­
pressor section and coil section. Remove fan and
motor-support panel assembly by removing six
sheet metal screws, three cap screws and dis­
connecting fan cable at control box. Then remove
coil end baffle.
Fan Adjustment — Turn unit power off. Remove
fan guard and loosen fan hub setscrew. Adjust fan
until surface of hub is 3/8 in. below top of venturi
rim as shown in Fig. 3. Then, tighten setscrew on
flat of motor shaft. Seal fan hub recess with
permagum to prevent hub from rusting to motor
shaft.
Lubrication
OUTDOOR FAN MOTORS have sealed bearings.
No provisions are made for lubrication.
COMPRESSOR has its own oil supply. Loss of oil
due to a leak in the system should be the only
reason for adding oil after system has been in
operation.
To Add or Remove Compressor Oil — Refer to
Carrier Standard Service Techniques Manual,
Chapter 1.