Carrier 38CQ - Manual (Page 13)

Fig. 29 - 38CQ048 with 40FS200/28MQ048
Cooling Cycle Charging Chart (R-22)
300
280
260
>240
fE 220
£ 180
140
120
WET-BULB TEMP
AIR ENT
OUTDOOR UNIT{F)
9F
-I0.5F
M
15 F
23.5F
33F
43F I
DRY-BULB TEMP
AIR ENT
INDOOR UNIT (F)
20 30 40 50 60
SUCTION PRESSURE AT SUCTION SERVICE PORT
70
Fig. 30 - 38CQ048 with 40FS200/28MQ048
Heating Cycle Operation Check Chart (R-22)
Unit Single-Phase Compressors
COMPRESSORS OF THE SPLIT CAPACITOR
(PSC) TYPE require an equalized system pressure
to start. When supply voltage is within 10% limit
and compressor does not start, give compressor a
temporary capacitance boost. See Carrier Standard
Service Techniques Manual, Chapter 2, for details.
Use a 130-mfd start capacitor. Connect wires with
insulated probes to each capacitor terminal. Touch
probes to each side of run capacitor or to
compressor motor terminals R and S. Start com­
pressor; pull probes away after 3 seconds Dis­
charge start capacitor. Run compressor for 10
minutes, then shut off and allow system pressure
to equalize. Try restarting without boost capacitor.
If after 2 attempts (without boost capacitor) the
compressor does not start, add an accessory start
thermistor (PTC device). If after 2 more attempts
the compressor does not start, remove thermistor
and add an accessory start capacitor relay package.
COMPRESSORS THAT ARE EQUIPPED WITH A
COMPRESSOR START THERMISTOR (PTC
device): if compressor does not start, check the
thermistor with an ohmmeter as described below.
Earlier unit models have a 50-ohm thermistor (with
2-prong connections), later models have a 25-ohm
thermistor (with 3-prong connections). If indoor
coil does not have a bleed-type expansion device, it
may be necessary to remove start thermistor and
replace with accessory start capacitor and relay.
Checking Start Thermistor
1. Shut off all power to unit and wait 5 minutes
for thermistor to cool to outdoor temperature.
2. Measure resistance of thermistor with ohm-
meter. Normal resistance readings at 75 F out­
door temperature are: 50 to 90 ohms for
50 ohm thermistor; 25 to 50 ohms for 25 ohm
thermistor.
3. If ohmmeter resistance reading is 0 or much
higher than 50 or 90 ohms, the thermistor is
defective and must be replaced.
If start thermistor is good and compressor does
not start, disconnect the thermistor from starting
circuit and give compressor a temporary capaci­
tance boost as described above. Run compressor
for 10 minutes, then shut off and allow system
pressure to equalize. Reconnect start thermistor
and try restarting compressor without boost capa­
citor. If aher 2 attempts the compressor does not
start, remove thermistor and add an accessory start
capacitor relay package.
13