MACS Monthly Newsletter - 2020 - OCT4

expansion valves and also prevent system control
problems. There are also electronic shut off valves
and diverter valves that can be used in conjunction
with TXVs of all sorts. While these specialty valves,
block valves and right angle valves can do many
things to achieve a multitude of system requirements, it is important to understand what the valve
is trying to do in your system.

* High evaporator and compressor superheat
* Short cycling of the low-pressure control
Do any of these symptoms sound familiar? Any
one of these can easily be associated with a low
refrigerant charge due to a leak in the system. It
is therefore important to first check for refrigerant
leaks and proper change level before replacing the
TXV.
In addition to low refrigerant charge level, what
are the issues associated with a defective TXV
which can cause the evaporator to freeze? One common cause can be excessive moisture in the system
which can freeze at the TXV's metering orifice (ball
seat) opening. As ice forms around this small opening, refrigerant flow can be blocked. This is another
common issue which might lead the service technician to diagnose a defective TXV when it actually may be a saturated receiver drier. If the system
has a moisture indicator, this will help diagnose a
saturated drier which can lead to moisture in the
system.
The TXV orifice can also plug and restrict refrigerant flow if dirt or foreign material is present in
the system. Can a dirty or plugged TXV be cleaned?
If the TXV is a block type, it is best to replace the
valve. If the TXV is a brass right angle type, check
to see if the valve has an inlet screen. If so, clean or
replace the screen. If there is no screen present, it is
best to replace the TXV.
Another common failure mode is power element
charge loss. Checking the basic function of the TXV
can be achieved by cooling the power element by

Troubleshooting Expansion Valves

Dianetti/Milliman

Dianetti/Milliman

Troubleshooting problems in a mobile air conditioning system can be a challenge. Some of the
symptoms of a defective TXV can be similar to other issues in the system. This may cause the service
technician to replace the TXVs when it is not defective. We will highlight some of the major issues
associated with troubleshooting TXVs in mobile air
conditioning systems.
Let's discuss common symptoms of a defective
TXV:
* Visible frost on the evaporator surface or
tubing (Figure 4)
* Frost coming through the air vents in the
vehicle passenger compartment

Figure 5: To diagnose a problem with the TXV, use ice or a
non-CFC cooling aerosol to change the temperature of the
power element when the system is running.

Figure 4: Frost on the evaporator tubing before entering the evaporator is a sure sign that something is not working properly.

October 2020

4

MACS Service Reports

MACS Monthly Newsletter - 2020

Table of Contents for the Digital Edition of MACS Monthly Newsletter - 2020

MACS Monthly Newsletter - 2020 - JAN1
MACS Monthly Newsletter - 2020 - JAN2
MACS Monthly Newsletter - 2020 - JAN3
MACS Monthly Newsletter - 2020 - JAN4
MACS Monthly Newsletter - 2020 - JAN5
MACS Monthly Newsletter - 2020 - JAN6
MACS Monthly Newsletter - 2020 - JAN7
MACS Monthly Newsletter - 2020 - JAN8
MACS Monthly Newsletter - 2020 - FEB1
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MACS Monthly Newsletter - 2020 - FEB3
MACS Monthly Newsletter - 2020 - FEB4
MACS Monthly Newsletter - 2020 - FEB5
MACS Monthly Newsletter - 2020 - FEB6
MACS Monthly Newsletter - 2020 - FEB7
MACS Monthly Newsletter - 2020 - FEB8
MACS Monthly Newsletter - 2020 - MAR1
MACS Monthly Newsletter - 2020 - MAR2
MACS Monthly Newsletter - 2020 - MAR3
MACS Monthly Newsletter - 2020 - MAR4
MACS Monthly Newsletter - 2020 - MAR5
MACS Monthly Newsletter - 2020 - MAR6
MACS Monthly Newsletter - 2020 - MAR7
MACS Monthly Newsletter - 2020 - MAR8
MACS Monthly Newsletter - 2020 - APR1
MACS Monthly Newsletter - 2020 - APR2
MACS Monthly Newsletter - 2020 - APR3
MACS Monthly Newsletter - 2020 - APR4
MACS Monthly Newsletter - 2020 - APR5
MACS Monthly Newsletter - 2020 - APR6
MACS Monthly Newsletter - 2020 - APR7
MACS Monthly Newsletter - 2020 - APR8
MACS Monthly Newsletter - 2020 - MAY1
MACS Monthly Newsletter - 2020 - MAY2
MACS Monthly Newsletter - 2020 - MAY3
MACS Monthly Newsletter - 2020 - MAY4
MACS Monthly Newsletter - 2020 - MAY5
MACS Monthly Newsletter - 2020 - MAY6
MACS Monthly Newsletter - 2020 - MAY7
MACS Monthly Newsletter - 2020 - MAY8
MACS Monthly Newsletter - 2020 - JUN1
MACS Monthly Newsletter - 2020 - JUN2
MACS Monthly Newsletter - 2020 - JUN3
MACS Monthly Newsletter - 2020 - JUN4
MACS Monthly Newsletter - 2020 - JUN5
MACS Monthly Newsletter - 2020 - JUN6
MACS Monthly Newsletter - 2020 - JUN7
MACS Monthly Newsletter - 2020 - JUN8
MACS Monthly Newsletter - 2020 - AUG1
MACS Monthly Newsletter - 2020 - AUG2
MACS Monthly Newsletter - 2020 - AUG3
MACS Monthly Newsletter - 2020 - AUG4
MACS Monthly Newsletter - 2020 - AUG5
MACS Monthly Newsletter - 2020 - AUG6
MACS Monthly Newsletter - 2020 - AUG7
MACS Monthly Newsletter - 2020 - AUG8
MACS Monthly Newsletter - 2020 - SEP1
MACS Monthly Newsletter - 2020 - SEP2
MACS Monthly Newsletter - 2020 - SEP3
MACS Monthly Newsletter - 2020 - SEP4
MACS Monthly Newsletter - 2020 - SEP5
MACS Monthly Newsletter - 2020 - SEP6
MACS Monthly Newsletter - 2020 - SEP7
MACS Monthly Newsletter - 2020 - SEP8
MACS Monthly Newsletter - 2020 - OCT1
MACS Monthly Newsletter - 2020 - OCT2
MACS Monthly Newsletter - 2020 - OCT3
MACS Monthly Newsletter - 2020 - OCT4
MACS Monthly Newsletter - 2020 - OCT5
MACS Monthly Newsletter - 2020 - OCT6
MACS Monthly Newsletter - 2020 - OCT7
MACS Monthly Newsletter - 2020 - OCT8
MACS Monthly Newsletter - 2020 - DEC1
MACS Monthly Newsletter - 2020 - DEC2
MACS Monthly Newsletter - 2020 - DEC3
MACS Monthly Newsletter - 2020 - DEC4
MACS Monthly Newsletter - 2020 - DEC5
MACS Monthly Newsletter - 2020 - DEC6
MACS Monthly Newsletter - 2020 - DEC8
MACS Monthly Newsletter - 2020 - DEC9
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