Commercial Air Conditioner
Model: heat pump, 10SEER UNITS
38
B. Measure from Start TERMINAL TO COMMON TERMINAL.
.Middle ohm value of the three measurements.
.Approximately 2.0 to 3.0 ohms
C. Measure from Start TERMINAL TO Run terminal.
.Highest ohm value of the three measurements.
.Approximately the sum of the first two measurements.
EXAMPLE:
Run to Common -1.0 Ohms
Start to Common -4.0 Ohms
Start to Run -3.0 Ohms
Good compressor motor :
Run to Common -
∞
Ohms
Start to Common -
∞
Ohms
Start to Run -3.0 Ohms
OPEN COMPRESSOR INTERNAL OVERLOAD-
ALLOW THE COMPRESSOR MOTOR TO COOL AND
THE INTERNAL OVERLOAD TO RESET.
Run to Common -1.0 ohms
Start to Common -
∞
Ohms
Start to Run -
∞
Ohms
OPEN COMPRESSOR START WINDING--
-REPLACE THE COMPRESSOR .
7.The resistance from one winding terminal to any other terminal should be the same with three phase
compressors.
NOTE:
on larger 208/230 volt compressors the ohm values could be as low as 0.10 ohms, THIS IS
NOT A SHORTED WINDING .A winding is open if resistance measured is infinite(
∞
).
COMPRESSOR MENCHANICAL CHECKS
Compressors fail mechanically due to bearing failure ,valve failure ,or damage to the internal suspension system.
Bearing and valve failure is almost always caused by liquid refrigerant .
COMPRESSORS CAN ONLY PUMP
REFRIGERANT VAPOR
.Liquid refrigerant damages the valves by deforming or breaking (slugging) them. It
damages the bearing by diluting the lubricating oil.
SYSTEM PUMP DOWN
This procedure tests the compressor valves .It can indicate internal refrigerant leaks such as through
the liquid line service valve. The procedure uses the compressor to trap all the refrigerant inside the
condensing coil (outdoor cooling) .The technician’s gauges indicate if the condensing coil holds the
refrigerant as intended or if it leaks out.
Procedure
1. Connect the compound refrigerant gauge to a service port that is always suction pressure such as
on the compressor shell, or in the line between accumulator and compressor. Connect the high
pressure gauge to a service port that is always high pressure .
2.
With the unit operating ,from seat (close) the liquid line service valve. Observe the gauges .The
suction pressure should fall. The high pressure should also fall slightly. If the discharge pressure
rises above 400 psi,
Shut off about outdoor unit.
3. SHUT OFF THE COMPRESSOR WHEN THE SUCTION PRESSURE DROPS TO 3-5 PSI.
POSITIVE PRESSURE .DO NOT OPERATE THE COMPRESSOR WITH A NEGATIVE SUCTION
PRESSURE.
4. Observe the suction pressure on the compound gauge.
