MACS Monthly Newsletter - 2020 - SEP8

use both O-rings and seals.
The slim line seal has a specific thickness and the
TXV is made to have this "pocket depth" surrounding the port. This pocket depth sets the proper
squeeze on the rubber portion of the seal. The seal
thickness and pocket depth change as the tube size
increases. These types of TXVs using slim line seals
are used by GM, Freightliner and others. See Figure
13.
The dual seal also has specific thickness which is
different than the slim line seal. The dual seals are
thicker than the slim line seals, so the TXV pocket
depth in the recessed area around the port is deeper. Just like the slim line seal, the dual seal pocket
depth in the TXV sets the proper squeeze to the
two rubber seals molded into it. These dual seals
are used mainly by Caterpillar but there has been
increased interest in these recently due to the need
for lower leak rates.

er element. The capillary tubes can have various
lengths for remote sensing capabilities. This means
that the capillary tube can be placed in different areas
on the evaporator to achieve different performance.
The right angle TXV offers internally equalized
options as well as externally equalized options,
again with various equalizer length tubes. The externally equalized valve gives you the option of
where the outlet pressure sensing is done. The connections for the right angle valves are limited due
to the size of the brass forging and are most times
English or metric tube-O. Some older right angle
valve models are made with flare fitting connections. See Figure 14.
As you can tell, the right angle valve requires
the user to know how their system operates so the
temperature sensing bulb and the equalizer pressure sensing is in the optimum position. The block
valve takes much of the guess work out of the equation and puts the temperature / pressure sensing in
the most effective place. With the added benefit of
being a more robust design (no capillary tubes to
break) and the added versatility of having multiple
types of connections. You can see why the block
valve has become more popular over the years for
mass production. n

Right Angle Valves

Dianetti/Milliman

There are TXVs that are not block valves as well.
The right angle valve was the predecessor to the
block valve and it has some useful advantages. The
right angle valve typically is constructed of brass
with a copper capillary tube in the top of the pow-

Figure 14: Different versions the right angle valve. On the left is a metric tube-O internally equalized valve, in the middle
is a standard externally equalized tube-O valve with a coiled pigtail on the sensing end and on the right is a standard,
externally equalized tube-O valve with a bulb assembly on the sensing end.
Keep an eye out for the October 2020 MSR, where Mike and Gene continue this topic with specialty valves,
system examples, thermal bulb placement and TXV troubleshooting. Thanks for reading!

MACS Service Reports is published monthly by the Mobile Air Conditioning Society
Worldwide. It is distributed to members of MACS Worldwide and is intended for
the educational use of members of the automotive air conditioning service and
repair industry. Suggestions for articles will be considered for publication, however,
MACS Worldwide reserves the right to choose and edit all submissions.

Editors:
Elvis Hoffpauir, Steve Schaeber
Production Designer:
Laina Forcey
Manager of Service Training:
Steve Schaeber
Mobile Air Conditioning Society Worldwide
P.O. Box 88, Lansdale, PA 19446
Phone: (215) 631-7020 * Fax: (215) 631-7017
Email: membership@macsw.org * Website: www.macsw.org

Unless otherwise noted, all photos/art by author.

September 2020

MACS Service Reports

http://www.macsw.org

MACS Monthly Newsletter - 2020

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