Scholar V VAIVA Maintenance & Service Manual 10/2017 Rev.2
34
6.1 Troubleshooting Recommendations
WARNING
DISCONNECT ALL POWER TO UNIT BEFORE SERVICING. CONTACTOR
MAY BREAK ONLY ONE SIDE. FAILURE TO SHUT OFF POWER CAN
CAUSE ELECTRICAL SHOCK RESULTING IN PERSONAL INJURY OR DEATH.
Unit is not running but you think it should be
1. Is power connected?
ס Look at HMI screen. If blank, power to unit may be off. Check circuit breaker.
Check voltage to unit.
ס If power is connected
■ Check HMI for correct operating mode and setpoints.
■ Look at status lights on PLC and see if compressor operation is called for. If
status light for compressor is ON:
»
Check for 24 VAC run signal on compressor driver board.
»
Check voltage on 500 ohm resistor on driver board. Should be between
1.0 and 6.35 VDC in cooling and between 1.0 and 9.4 VDC in heating
(adjustable if needed in mild ambients to limit head pressure).
2. If compressor will not run, look through plastic sight glass on controls cover and count
the flash code. The flash code can give information regarding conditions the driver
has seen that can stop compressor operation. See the list of flash codes previously
discussed in this manual.
Compressor is running but cooling or heating capacity seems to be inadequate
1. Possibly low on refrigerant. If this turns out to be the case, there is likely a leak in the
system.
ס Look at EEV display (Part 18). Is superheat being controlled? If superheat is very
high or valve is open 100%, a leak may be indicated.
ס Look at refrigeration sight glass (Part 15). If lots of bubbles are continuously visible
with compressor running, a leak may be indicated.
ס Before adding any refrigerant, a meaningful attempt should be made to isolate and
repair leak, using acceptable refrigeration practices.
■ Be sure Schraeder caps are in place and are tight (Items 37 and 38).
■ Look for signs of refrigerant oil on components. This can often pinpoint a leak.
■ Use an electronic leak detector. Large leaks can sometimes be found with
soap bubbles.
2. Cooling or heating set-point set too high or low respectively.
ס When the set-point is reached, the compressor does not typically shut off but runs
at a lower than maximum speed. Check set-points on the HMI screen. Toggle to the
second screen on the HMI display and see what speed control voltage is being sent
to the compressor driver board.
ס In cooling, if the voltage is showing 6.35 VDC, that means that the PLC should be
sending the maximum speed signal for cooling to the driver board. In heating, the
maximum voltage is 9.4 VDC. Check this voltage on the driver board with a VOM.
It should measure the same voltage as indicated on the HMI screen. If the proper
voltage is not being delivered, that could indicate an issue with the analog output on
the PLC. Be sure to check the resistor to be sure the terminals are tight. Check the
resistance value with a VOM to be sure it is 500 ohms +/- 10%.