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SER04-339-16-04

Service Diagnostic Guide for R404A TXVs

14-00232-25SV (replaces 14-00232-02SV) Ultima 53 & Ultra XT/XTC R404A

14-00232-26SV (replaces 14-00232-05SV) Ultra, Ultra XL, Extra, Mach 10, Optima R404A

14-00232-28SV (replaces 14-00232-12SV) Ultima XTC (W/suction mod valve) R404A

14-00232-29 (replaces 14-00232-14) Extra XT R404A

Table-1 (TXV Part Numbers)

The expansion valves in Table-1 above are not field-adjustable. The superheat hasbeen pre-set by the manufacturer to accommodate a wide range of ambient and boxtemperatures and accurate adjustment in the field is not possible.

The power heads and valve assemblies on these TXVs are matched and are notinterchangeable.

The tolerance of the manufacturers specification, which determines the superheat, wastightened on these valves to reduce variability and improve performance.

These TXV part numbers may change over time. Please refer to the current part list for theunit model number.

Superheat Test:

The superheat varies with box and ambient temperature.

Normal field superheat

o 0F box temperature, 100F ambient or discharge pressure 300-350psigo Temperature measured at the TXV sensing bulb wrapped with Presstiteo Pressure measured at the suction port on the suction service valve

Checking Superheato Remove evaporator panel from rear of unit and then pull loose the Presstite insulation

from one end of the expansion valve bulb.o Loosen one TXV bulb clamp and make sure area under clamp (above TXV bulb) is

clean.o Place thermocouple above (parallel) TXV bulb and then secure loosened clamp

making sure both bulbs are firmly secured to suction line as shown in Figure-1 below.Use Presstite insulation to completely cover both bulbs.

1. Suction Line2. TXV Bulb Clamp3. Nut and Bolt (Clamp)4. Thermocouple5. TXV Bulb

Thermostatic Expansion ValveBulb and Thermocouple

Figure-1Serv

iceInformation

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NOTE: In order to obtain the proper operating parameters for testing superheat, it may be necessaryto reduce the size of the refrigerated compartment by installing a flexible bulkhead. This will bring thebox temperature down quickly to the desired temperature of 0F. It may also be necessary to partiallyrestrict the airflow to the condenser in order to raise the head pressure to 300psig.

Connect an accurate gauge to the 1/4 (6.4mm) port on the suction service valve.

Run unit in cool mode until stabilized at 0F. Set controller 10F (5.5C) below boxtemperature.

Ensure the discharge pressure is 300-350psig. Record the suction pressure and the temperature of the suction gas at the expansion valve

bulb at least five times at two to three minute intervals. These two measurements should betaken at the exact same time.

From the temperature/pressure chart, determine the saturation temperature corresponding toeach of the suction pressure readings.

Subtract the saturation temperature from the temperature measured at the expansion valvebulb for each of the sets of readings. This difference is the superheat of the suction gas.

Average the five superheat measurements.

The superheat should be 12-20F (6.7-11.1C)

TXV MOP Test:

The Maximum Operating Pressure of the TXV limits the flow of refrigerant to the evaporator at highsuction pressure conditions to ensure the diesel engine is not overloaded. To test the MOP, thesuction pressure will be pulled down below the MOP by running a low side pumpdown. Refrigerantwill then be trickled in slowly, raising the suction pressure to the point the TXVs MOP limits the flow ofrefrigerant to the evaporator. In order to perform this test, the box temperature must be high enoughto have an evaporator coil temperature capable of producing a suction pressure higher than the MOP.

The box temperature must be higher than 52F for Ultima XTC and 40F for all other model units.

Follow these steps to test the MOP:

Step:

1. Box temperature is 52F for Ultima XTC and 40F for all other model units.2. Install a set of manifold gauges

3. For units equipped with an SMV, run unit in high-speed heat. After 30 seconds, unplug theSMV.

4. Switch to high-speed cool.5. Run a low side pump down procedure by front seating the king valve.6. Disconnect the connector to SV2.7. Shut unit off.8. Open the king valve.9. While monitoring suction pressure, slowly release refrigerant into the low side of the

system by pulsing 12 VDC power to SV2.10. Suction pressure should rise to the MOP setting and level.

14-00232-25SV 55 MOP Ultima & Ultra XT/XTC R404A

14-00232-26SV 35 MOP Ultra, Ultra XL, Extra, Mach 10, Optima R404A

14-00232-28SV 105 MOP Ultima XTC R404A14-00232-29 60 MOP Extra XT R404A

Table-2 (MOP values)Observations

Superheat increases as the ambient temperature reduces from the 100F rating temperature.This is due to the corresponding reduction in pressure differential across the TXV causing adecrease in refrigerant flow.

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Superheat decreases as the box temperature reduces because of the valves design and a

reduction in the amount of available heat in the box being transferred to the refrigerant seeChart-1 below.

Chart-1

Suction line frosting is not always an indication of low superheat or flooding. Low suction

temperatures below the ambient air dew point will result in moisture condensing on the suctionline and freezing.

Frosting at the compressor heads is a good indication of low superheat because the heat fromthe discharge side of the head should be enough to keep the suction side from frosting.

TD (dealers only)

Effect of Ambient and Box Temperature on Superheat

14-00232-26

0

10

20

30

40

50

60

35F Box 0F Box -20F Box

Superheat(F)

100F Ambient

65F Ambient

6 Cylinder

6 Cylinder 6 Cylinder

4 Cylinder