8
2.5 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 o access valve while servicing. This will prevent contamination
of the system and/or refrigerant from leaking. AFTER SERVICING, THE ACCESS VALVE SHOULD BE REMOVED. A pinch-o tool can
be used to close the system to remove the access valve and then braze the hole for the access valve to seal the system. Be sure to
leak check after brazing.
2.6 preSSUre anD temperatUre
There are a couple of ways to measure temperature of the evaporator plate:
Use a thermocouple to measure the temperature of the evaporator plate. The thermocouple must be secured to the evapora-1.
tor when taking the measurement. The best and most accurate location for the thermocouple end is where the thermistor is
secured to the evaporator. Allow anywhere from three to six degrees F of variation in measured temperatures if you measure
on the plate because of the thermal conductivity of the thermistor body in comparision to the thermocouple.
If it has been determined that there is proper contact between the thermistor and evaporator plate, the thermistor resistance 2.
value can be corresponded to the temperature (see Table C in Section 5.2, Thermistors, for values).
If it has been determined that there is proper contact between the thermistor and the evaporator plate, the voltage at the 3.
thermistor terminals can be read. The voltage can be read while the unit is running by attaching test leads to thermistor ter-
minals 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 cycle is 45 degrees F and the corresponding voltage is 2.88V. Slight
variations in actual measurements can occur due to input voltage variations.
NOTE: THE TEMPERATURE AND PRESSURE READINGS MUST BE TAKEN WITH THE UNIT ON AND WATER FLOWING OVER THE EVAPO-
RATOR PLATE (IN THE PRODUCTION CYCLE). USE GAGE PRESSURE READINGS FROM THE COMPRESSOR’S PROCESS TUBE (LOW
SIDE) ACCESS VALVE.
Table B: 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
-8 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
SEALED SYSTEM
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