Mitsubishi Electric CITY MULTI PUHY-400YMF-C Service Handbook page 130

6) SV6
When No. 2 compressor is operating and No. 2 compressor is stopped, the main SV6 will be set to ON, making it
possible to confirm operation by monitoring the LED display and listening to the operating sound. Note that it may be
set to OFF if the outlet temperature (TH11) exceeds 120°C .
7) 21S4a
This 4-way switching valve operates as follows.
Not conducting : There is conductivity between the outlet port of the oil separator and the heat exchanger (HEX1a, 2a:
the heat exchanger to the right when facing the front of the unit) and between the gas ball valve (BV1)
and accumulator, forming the cooling cycle circuit.
Conducting: There is conductivity between the oil separator and the gas ball valve and between the heat ex-
changer and accumulator, forming the heating cycle circuit.
It is possible to determine whether or not there is normal operation by monitoring the LED display and the temperature
of the inlet and outlet ports of the 4-way switching valve at that time. By monitoring these, it is possible to determine the
areas where there is conductivity. Do not confirm the temperature of the piping on the oil separator side by touching it.
It is extremely hot.
* Prevent the outside from receiving impact. If the outer ring becomes deformed, the inner valve will not operate
properly.
8) 21S4b
This 4-way switching valve operates as follows.
Not conducting : There is conductivity between the outlet port of the oil separator and the heat exchanger (HEX1b, 2b:
the heat exchanger to the left when facing the front of the unit).
Conducting: There is conductivity between the heat exchanger and the accumulator.
The heat exchanger circuit opens and closes during cooling and heating.
While it is possible to determine whether or not there is normal operation by monitoring the LED display and the sound
of the switching, the switching of the 21S4a during heating is heavier, which could make confirmation by sound more
difficult. At this time, it is possible to determine the areas where there is conductivity by the temperature of the inlet and
outlet temperatures of the 4-way switching valve. Do not confirm the temperature of the piping on the oil separator side
by touching it. It is extremely hot.
* Prevent the outside from receiving impact. If the outer ring becomes deformed, the inner valve will not operate
properly.
Constant Capacity Unit Valves (SV1, SV2, SV3, SV4, SV5b)
Check if the control board's output signals and the operation of the solenoid valves match.
Setting the LED monitor display switch (SW1) as shown in the figure below cases the ON signal of each relay to be
output to the LEDs.
* When monitoring the constant capacity unit, set SW4-2 ON.
Each LED shows whether the relays for the following parts are ON or OFF. When a LED lights up, it indicates that the
relay is ON.
SW1
SW4-2
1 2 3 4 5 6 7 8 9 0
Compressor
0 0 0 0 0 0 0 0 0 0 ON
Operating
1 0 0 0 0 0 0 0 0 0 ON
1) SV1 (Bypass Solenoid Valve)
This solenoid valve opens when conductive (relay ON).
1 Since SV1 will be set to ON 3 minutes after the constant capacity unit compressor has started operation, confirm
operation by monitoring the LED display and listening for the operation sound of the solenoid valve.
2 By measuring the changes in temperature of the SV1 outflow pipe while it is conducting, it can be determined
whether the valve is open or closed. When the valve is open hot gas will flow down the pipe, so do not check it by
touch. (Since the parallel capillaries will still carry hot gas when the valve is shut, the outflow pipe will always be
hot).
1 2 3
52C1
SV4 SV5b
LED
4 5
21S4-1 SV1
CH2, 3
-127-
6 7 8
SV2, 3
Lights up all
(PUHN-P-
the time
YMF-C only)
52F