Carrier R-22 Application Manual And Service Manual page 15

5. Try restarting compressor without boost capacitor. If after 2
attempts compressor does not start, remove thermistor. Add an
accessory start-capacitor relay package.
TEMPORARY CAPACITANCE BOOST
Do not under any circumstances attach a temporary boost
capacitor directly to the compressor terminals. Serious per-
sonal injury can result. Exercise extreme caution with this
procedure when high-voltage power is on.
There are times when a temporary capacitance boost is needed to
get compressor started. (See Fig. 14.) If compressor motor does not
start, it may be due to low-line voltage, improper pressure
equalization, weak run capacitor, or a seized compressor. Check
each possibility and attempt capacitance boost before adding
auxiliary start capacitor and relay.
1. Turn off all power to unit. There may be more than one power
source to condensing unit.
NOTE: If a PTC is already installed, remove it from the system
by pulling PTC wires from H. and C terminals on run capacitor.
2. Check compressor for ground or open windings. If winding's
resistance is within manufacturer's recommendations, pro-
ceed. (See Section on proper compressor-winding check.)
Do not check winding at compressor terminals with pressure
in the system. Check resistance by removing wires attached at
the compressor contactor and run capacitor.
3. Obtain a start capacitor in the range of 150–180µF volts rating.
Connect 8–gauge wires with insulated clips or terminals to the
H. and C terminals of the run capacitor.
4. Turn power on to unit. If compressor starts, immediately
remove start-capacitor wires from H. and C terminals of run
capacitor, using a pair of insulated, needle-nose pliers. DO
NOT leave start capacitor attached to run capacitor for more
than 3 seconds, even if compressor doesn't start.
L2
FIELD POWER
SUPPLY
L1
C
Start capacitor
(SC)
temporarily
connected
Capacitance boosting
Fig. 14—Capacitance Boosting
5. Discharge start capacitor by using a pair of insulated, needle-
nose pliers and shorting a 15,000–ohm, 2–watt resistor across
terminals.
NOTE: Some start capacitors already have a bleed resistor
attached. If so, it will discharge itself over a short period of time.
6. Run compressor 10 minutes. Stop and allow unit to sit idle for
5 minutes.
7. Check system pressure equalization.
8. Attempt to restart without capacitance boost.
If PTC thermistor device is inadequate as start device, a start
capacitor and relay may be added to system to ensure positive start.
Capacitor is wired in parallel with run capacitor through normally
closed set of contacts on a device called start relay. The relay coil
is wired across start and common terminals of compressor. The
added capacitance gets the compressor started. As compressor
comes up to speed, voltage across start and common terminals
increases to a value high enough to cause start relay to energize.
This opens normally closed contacts and removes start capacitor
from circuit. In actual practice, this occurs in a fraction of a
second.
NOTE: If bleed resistor is wired across start capacitor, it must be
disconnected to avoid erroneous readings when ohmmeter is
applied across capacitor.
To check start relay and capacitor:
1. Turn off all power to unit.
2. Discharge start and run capacitors as outlined earlier.
3. Most start capacitors will have a 15,000-ohm, 2-watt bleed
resistor. Disconnect these devices from system.
Start capacitor can be inspected visually. It is designed for short
duration or intermittent duty. If left in circuit for prolonged period,
start capacitor blows through a specially designed bleed hole. If it
appears blown, check for welded contacts in start relay. Start
capacitor can be checked by ohmmeter method discussed earlier.
Start relay is checked with ohmmeter. Check for continuity across
coil of relay. You should encounter a high resistance. Since relay
contacts are normally closed, you should read low resistance
C COMP
SC
15
R
S
RC
C
A00195