Trane RTWA 70-125 TON - Manual (Page 40)

40 RLC-SVD03A-EN
Compressor Capacity
ƽ WARNING
Live Electrical Components!
During installation, testing, servicing and troubleshooting of this
product, it may be necessary to work with live electrical
components. Have a qualified licensed electrician or other
individual who has been properly trained in handling live
electrical components perform these tasks. Failure to follow all
electrical safety precautions when exposed to live electrical
components could result in death or serious injury.
With a particular compressor running, the relay may be checked (under load,
as explained above) by measuring the voltage from terminal J7-9 to the 115
VAC neutral. The relay operates in the high side and switches power from
J7-8 to J7-9, to move the step load valve to the loaded position. When the
CPM decides to load the compressor, the step load solenoid is energized
continuously. To assure that loading and unloading is occurring, it may be
necessary to make slight adjustments to the chilled water setpoints to force
action.
Checkout Procedure for Step Load Solenoid Valve
and Piston
Prior to a compressor start, connect a pressure gauge to the Schrader port
near the step load solenoid valve. This port is connected to the back side of
the step load piston and, therefore, will allow direct measurement of the
pressure that actuates the step load valve. Observe the pressure gauge
during a compressor start, either from a manual compressor test or a normal
call for cooling. Initially, the pressure should drop to the suction pressure and,
when the MCSP calls for compressor loading, the solenoid will actuate and
supply discharge pressure to the piston. If, after verifying that 115 VAC has
been applied to the step load solenoid, the pressure does not increase to
discharge pressure, the step load solenoid coil and/or valve must be replaced.
Also, when the solenoid valve is energized and the piston pressure is near
discharge pressure, the percent RLA of the compressor, as seen in the
Compressor Report, should increase. If the percent RLA does not increase,
the step load valve is stuck and should be repaired.