Carrier 38AD - Liquid Line Pressurestat Installation; Defrost Thermostat Installation; Fan Adjustment Procedure; Compressor Lubrication Guide

allow unit to start under low-ambient conditions.
An evaporator freezestat must also be installed in
series with the control thermostat(s) to prevent
coil freeze-up (See lower part of Fig 15 - EDT
Wiring section.)
LIQUID LINE PRESSURESTAT - Connect to
system liquid line service valve port. Connect
switch into control circuit as shown on unit label
diagram or in Fig. 15. Pressurestat is set to cutout
at 5 psig with a differential of 10 psig. Do not
change setting
Fig. 15 — Unit Wiring Changes for
Winter Start Control
DEFROST THERMOSTAT — Position switch so
that moisture cannot enter switch insulator. Install
control with approximately 2 in. of top of thermo¬
stat capillary passing thru lower part of evaporator
coil and with remainder of capillary inserted
between fins on entering air side of coil. Connect
thermostat electrical contacts into indoor cooling
thermostat circuit or in series with compressor
holding coil.
Thermostat is set to cut out at 25 F and cut in
at 55 F. Contact rating is 16 amps and 230 volts.
As evaporator coil frosts, coil fin temperature
drops to thermostat cutout setting, and stops
compressor. Evaporator fans keep running to
defrost coil with room air. As indoor coil defrosts,
fin temperature will rise to thermostat cut-in
setting. Compressor starts when cooling is required.
NOTE. Use a defrost thermostat on all systems
operating with outdoor temperatures below 45 F.
Fan Adjustment — When replacing a fan, adjust fan
until top surface of hub plate is below the top of
the orifice ring as indicated in Fig. 16. Then,
tighten both setscrews, located over the keyway of
the fan hub of the motor shaft. Seal recessed area
of fan hub bore with Permagum to prevent rusting.
Lubrication
FAN MOTORS have permanently lubricated bear¬
ings. No provisions for lubrication are made.
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 the system has been in
operation.
To Add or Remove Compressor Oil
1. Stop compressor and close suction service valve.
Pump down compressor to 2 psig. Stop com¬
pressor and close discharge shutoff valve.
2. Relieve crankcase pressure by disconnecting
line, at compressor, which goes to low-pressure
connection of oil safety switch.
3. Add oil thru oil filter connection.
4. Remove oil thru drain plug in bottom cover.
Remove small amounts of oil thru oil discharge
connection with compressor running.
Fig. 16 — Fan Adjustment
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