Commercial Air Conditioner
Model: heat pump, 10SEER UNITS
37
drop tables are available ,they indicate the cubic feet of air per minute(CFM) moving through the coil .An inclined
manometer is an example of this type of instrument.
A velometer measures the velocity of the air in feet per minute(FPM). If the area of duct is known, the velometer
reading times the area of duct (in square feet ) calculates the air flow.
There are also simple mathematical formulas that are needed. All of them require measurement be taken .These
measurements require a voltmeter, ammeter and a good temperature tester.
Caution:
these following procedures can only be done with electric resistance heaters.
▼
CFM
(Electrical Heater) =VOLTS
×
AMPS
×3.414
1.08
×
TEMP
RISE
COMPRESSOR AND SYSTEM FAULT DIAGNOSIS
Many returned compressors have nothing wrong with them. To ensure that does not happen, the
technician must determine if the compressor has failed or if another control has either failed or stopped
the compressor after detecting a problem .The following procedures should help determine if the
compressor has failed.
Prior to replacing a suspected failed compressor
，
a thorough check must be made of all existing
electrical components .If not done ,a replacement compressor might also failed or not operate at all.
WARNING: THE FOLLOWING PROCEDURES SHOULD ONLY BE ATTEMPTED BY A QUALIFIED LICENSED
SERVICE TECHNICIAN EQUIPPED WITH PROPER TOOLS AND INSTRUMENT SUCH AS A REFRIGERANT
RECOVERY ,VACUUM PUMP ,VOLTMETER ,AMMETER,OHMMETER ,THERMOMETERS,PRESSURE
GAUGES,MICRON METER,,ETC.
COMPRESSOR ELECTRICAL CHECKS
Single-phase compressors use permanent split capacitor motors. There are two windings that connect at a common
point at the “common” wiring terminal. The two windings are called “start” and “run”. The start winding has the
higher resistance and is connected in series with the capacitor. The run winding has the lower resistance and
connects directly to the power supply from the compressor contactor.
The design use a protective device called an “internal overload” .if it detects either dangerously high amperages or
temperatures in the compressor motor ,it opens an internal circuit to stop the motor.
ELECTRICAL CHECK COMPRESSORS
1
．
Consult the unit wiring diagram .Determine that all electrical wiring for the units is correct and that all
wiring connections are right.
2
．
Measure the available line voltage .
A. On the single phase 208/230Volt units ,this should be from 197 to 253 Volts.
3.Check for proper control voltage at the unit contractor coil . If this voltage is inadequate or is not present ,refer
to the wiring diagram or the compressor troubleshooting flow chart at the end of this section for possible causes.
4.Remove all power from the unit and visually inspect the compressor contactor for pitted or burned points.
A. This could indicate high or low voltage problems or improper start components.
B. check the contactor coil with an ohmmeter for a short or open circuit.
C. Replace the contactor if any fault is noted.
5
.WITH THE ELECTRICAL POWER OFF
, remove all power wires from the compressor terminals ,
MARK
THE ORIGINAL LOCATION OF EACH WIRE.
A. Use an ohmmeter set for the highest scale to check for grounding between compressor motor terminals and a
good clean ground such as the compressor shell or copper line.
B. The resistance from any terminal to ground should exceed 1,000,000 ohms.
6.Use an ohmmeter set for the lowest scale and check the continuity of the motor windings .These ohm values are
less than ten ohms and in some cases less than one ohm.
A .Lowest from RUN terminal to common terminal.
.lowest ohm value of the three measurements.
.Approximately 1.0 ohms
