© 2009 Viking Preferred Service
15
Access Valves
A temporary access valve can be used to service
or evaluate the system. The access valve can be
installed on the compressor’s process tube (this
will also be a low pressure side). Be sure to cap
off access valve while servicing. This will prevent
contamination of the system and/or refrigerant from
leaking. AFTER SERVICING, ACCESS VALVE
MUST BE REMOVED. A pinch-off tool can be used
to close the system to remove access valve and
then braze the hole for access valve to seal the
system. Be sure to leak check after brazing.
Pressure and Temperature
There are a couple of ways to measure temperature
of the evaporator plate:
1. Use a thermocouple to measure temperature
of evaporator plate. The thermocouple
must be secured to evaporator when taking
measurement. The best and most accurate
location for the thermocouple end is where
the thermistor is secured to evaporator.
Allow anywhere from three to six degrees F
of variation in measured temperatures if you
measure on the plate because of thermal
conductivity of thermistor body in comparision
to thermocouple.
2. If it has been determined that there is proper
contact between thermistor and evaporator
plate, thermistor resistance value can be
corresponded to temperature
(“Resistance
versus Temperature Chart” page 27).
3. If it has been determined that there is proper
contact between the thermistor and the
evaporator plate, the voltage at the thermistor
terminals can be read. The voltage can be
read while the unit is running by attaching test
leads to thermistor terminals at the electronic
control. The temperature to switch into harvest
cycle is 11 degrees F and the corresponding
voltage is 3.77V. The temperature to switch into
the production cyle is 45 degrees F and the
corresponding voltage is 2.88V. Slight variations
in actual measurements can occur due toinput
voltage variations.
Note:
the temperature and pressure readings
must be taken with unit on and water flowing over
evaporator plate (in production cycle). Use gage
pressure readings from compressor’s process tube
(low side) access valve.
Refrigeration Temperature/Pressure Chart
for R-134a
Degrees
F
Pressure (psi)
R-134a
Degrees
F
Pressure (psi)
R-134a
-12
1.1
36
31.3
-9
2.8
38
33.2
-4
4.5
40
35.1
0
6.5
42
37.0
2
7.5
44
39.1
4
8.5
46
41.1
6
9.6
48
43.3
8
10.8
50
45.5
10
12.0
52
47.7
12
13.1
56
52.3
14
14.4
60
57.5
16
15.7
64
62.7
18
17.0
68
68.3
20
18.4
72
74.2
22
19.9
76
80.3
24
21.4
80
86.8
26
22.9
84
93.6
28
24.5
88
100.7
30
26.1
92
108.2
32
27.8
96
116.1
34
29.5
100
124.3
During production cycle, low side pressures will vary
anywhere from 140 psi to 2 psi, depending at what
point measurements are taken. High side pressures
can range from 481 psi to 25 psi also depending at
what point measurements are taken.
Service Diagnostics and Procedures
(Sealed System)
