Figure 7.20 Thermostatic Expansion Valve Bulb - Carrier 69NT40-541-505 Operation And Service Manual

The surface corrosion of aluminum is brought about by
exposure to chemicals such as sulfur dioxide and pos-
sibly other fumigants that are commonly used for fumi-
gation and protection of some perishable cargo such
as grapes, for example. Fumigation is the process by
which a chemical is released into an enclosed area to
eliminate infestations of insects, termites, rodents,
weeds and soil−born disease.
Typically any aluminum oxide that becomes detached
from evaporator fan stators will be blown into the wet
evaporator coil where it will be caught and then flushed
out of the unit during routine defrost cycles.
However, it is still highly recommended that after carry-
ing cargo subject to fumigation procedures, that the
inside of the unit be thoroughly cleansed prior to reuse.
Carrier Transicold has identified a fully biodegradable
and environmentally safe alkaline cleaning agent
(Tri−Pow'r® HD) for the unit. This will assist in helping
to remove the corrosive fumigation chemicals and dis-
lodging of the corrosive elements.
This cleaner is available from the Carrier Transicold
Performance Parts Group (PPG) and can be ordered
through any of the PPG locations; Part Number
NU4371−88.
As a general safety precaution, before using this prod-
uct, refer to and retain the Material Safety Data
(MSDS) sheet. This document can be found at:
www.nucalgon.com/products/coil_cleaners_tripower.htm
Prior to Cleaning:
− Always wear goggles, gloves and work boots.
− Avoid contact with skin and clothing, and avoid
breathing mists.
− When mixing, add water to the sprayer first, then the
cleaner.
− ALWAYS provide for proper ventilation when cleaning
indoor evaporator coils (rear doors must be open).
− Be aware of surroundings − food, plants, etc., and
the potential for human exposure.
− Always read directions and follow recommended dilu-
tion ratios. More is not always better. Using
non−diluted cleaner is not recommended.
Cleaning Procedure:
a. Remove the upper evaporator access panel
inside of the unit.
b. Spray the surface with water before applying the
cleaning solution. This helps the cleaner work better.
c. Liberally apply the prepared cleaner solution (5
parts water and 1 part cleaner).
d. Allow the cleaner to soak in for 5 to 7 minutes.
e. Assess area for rinsing. Follow all local regula-
tions regarding disposal of waste water.
f. Thoroughly rinse the cleaner and surrounding
area, floor, etc. When rinsing where heavy
foaming solution is present, it is very important
to take the time to thoroughly rinse the equip-
ment and surroundings.
T-368
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g. Always rinse the empty coil cleaner bottle, cap
tightly and dispose of properly.
7.16 THERMOSTATIC EXPANSION VALVE
The thermostatic expansion valve (TXV) (see
3.2) is an automatic device that maintains constant
superheat of the refrigerant gas leaving the evaporator,
regardless of suction pressure.
TXV functions are:
1. Automatic control of the refrigerant flow to
match the evaporator load.
2. Prevention of liquid refrigerant entering compressor.
Unless the valve is defective, it seldom requires main-
tenance other than periodic inspection to ensure that
the thermal bulb is tightly secured and properly insu-
lated. See Figure 7.20.
TXV Bulb Clamp is soldered to the suction line.

Figure 7.20 Thermostatic Expansion Valve Bulb

1. Suction Line
2. Thumbscrew
3. TXV Bulb Clamp
4. TXV Bulb
5 Foam Insulation
7.16.1 Checking Superheat
Proper superheat measurement should be
completed at -18°C (0°F) container box tem-
perature where possible.
a. Open the upper right (EFM#1) access panel
(see Figure 3.1) to expose the expansion valve.
b. Attach a temperature sensor near the expansion
valve bulb and insulate. Make sure the suction line is
clean and that firm contact is made with the sensor.
c. Connect an accurate gauge to the service port
directly upstream of the suction modulating valve.
d. Set the temperature set point to -18°C (0°F) and
run unit until conditions stabilize.
e. The readings may cycle from a high to a low reading.
Take readings of temperature and pressure every
three to five minutes for a total of 5 or 6 readings.
f. From the temperature/pressure chart
6), determine the saturation temperature corre-
sponding to the evaporator outlet test pressures
at the suction modulation valve.
g. Subtract the saturation temperatures in step f
from the temperatures measured in step e. The
difference is the superheat of the suction gas.
Determine the average superheat. It should be
4.5 to 6.7°C (8 to 12°F).
7–16
Figure
NOTE
2
1
5
4
NOTE
(Table 7–
3