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GRANT LAIDLAW
Grant Laidlaw is currently the owner of the Air Conditioning and Refrigeration Academy (ACRA) in Edenvale.
He holds a Bachelor of Business Administration and an associate degree in educational administration. He
has a National Technical Diploma and completed an apprenticeship with Transnet. He has dual-trades status:
refrigeration and electrical. He has been involved with SAIRAC for 17 years and has been a Johannesburg
committee member for the past eight (chairman in 2011 and 2012). Currently he is the treasurer
(Johannesburg council) as well as president (national council).
PROPER POSITIONING OF
TEV BULB
By Grant Laidlaw
THERMOSTATIC EXPANSION VALVE (TEV) BULB
LOCATION
Hi Sarel. The thermostatic expansion valve sensing bulb that
controls the thermostatic expansion valve is clamped to the
refrigerant suction line where it monitors the temperature. The TEV
should be installed as close as possible to the evaporator coil inlet.
The expansion valve body is installed in the liquid refrigerant
line ahead of the evaporator coil. The sensor bulb is to be fastened
to the suction line as close to the evaporator as possible.
For TEVs that use external pressure equalisation, the
equalising pressure line must be connected to the suction line
immediately after the temperature sensing bulb that operates
the TEV. In addition, it is good practice to connect the equalising
line to the top (twelve o’clock position) of the suction line.
This prevents oil and possible liquid refrigerant ingress into
the equalising line which may cause erratic operation of the
expansion valve.
As far as location is concerned, one manufacturer differs
from the next. Some state the twelve o’clock position while
others the one o'clock position. Always follow the manufacturer's
specification. The twelve and one o’clock positions are typically
for small suction lines up to 19mm in diameter.
www.hvacronline.co.za
Feeler Bulb placed in the twelve-o clock position.
This contrasts with a system that that uses a larger diameter line
(more than 19mm in diameter). In this case the thermostatic
expansion valve sensor bulb is clamped at the four or eight o’clock
position on the lower portion of the suction line.
Sarel asks: Hi Grant, some time ago I ran into information
with regards to expansion valve feeler bulb location
not always in the 12 o’clock position. We have just lost
a compressor due to the expansion valve feeler bulb
incorrectly installed. What about evaporators with multiple
expansion valves? Could you help on this as well as
expansion valves hunting. Thanks.
Many people ask for assistance in the understanding of theoretical and
practical aspects of the industry. I will endeavour to enlighten.
Feeler Bulb placed in the four o’clock position .
Some manufacturer’s specifications provide more detail such
as: “The bulb is best mounted on a horizontal suction line tube
and in a position corresponding to between one o'clock and
four o'clock. The location depends on the outside diameter of
the tube.”
This is to give a more accurate reading, since, should any
liquid refrigerant be present in the suction line exiting the
evaporator, this liquid refrigerant will most likely be found just
above the oil flowing on the bottom of the tubing on its way
back to the compressor.
The intent is to place the TEV's sensing bulb close to but
above the level of liquid refrigerant in the line. For larger diameter
refrigerant tubing the two, three, or four o'clock position may be
RACA Journal I April 2020
59