19
3.8 ORIFICE SIZE
The piston model air handler comes standard with a flow check piston installed. The pis-
ton may need to be changed to a different orifice size depending upon the outdoor unit.
The following table lists the recommended orifice size for various outdoor units.
*Piston size installed at factory. Correct piston for other tonnages will be included with the
matching outdoor unit.
3.9 REFRIGERANT LINE CONNECTIONS & CHARGING
3.9.1 PREPARATION
The coil is shipped with a low pressure (5-10 psig) charge of dry nitrogen which will be
released when the rubber plugs are removed. Leave the rubber plugs in the refrigerant con-
nection stubs on the air-handler until the refrigerant lines are ready to be brazed to the refrig-
erant connection stubs to prevent contaminants from entering the coil. Clean the ends of
the tubing and coil connection stubs (inside and outside) with an alcohol wipe before insert-
ing the line set tubes into the coil connection stubs to assure a quality leak-free braze joint.
Refer to the outdoor unit installation instructions for details on refrigerant line sizing and
installation. Be sure to follow long line length guidelines if they apply.
Route the refrigerant tubing in a manner than does not block service access to the front
of the air-handler.
3.9.2 LIQUID LINE FILTER DRIER
A new liquid filter drier must be installed every time any part of the system has been
open to the atmosphere, even if it’s for a short period of time. The filter drier should be
installed close to the air-handler for a system started up in the cooling mode and near
the outdoor unit for a heat pump system started up in the heating mode. This allows the
filter drier to catch any contaminants in the liquid line before they can enter the indoor or
outdoor TXV inlet screen.
3.9.3 BRAZING
Air inside the tubing and coil should be displaced with dry nitrogen prior to the brazing
process to prevent the formation of harmful copper oxide inside the tubing. It is very
important not to pressurize the system with nitrogen while brazing or pin-hole leaks will
form in the braze joint. This is accomplished by removing the gauge port valve core on
one of the outdoor unit service valves to allow the pressure to be relieved as the heated
nitrogen expands. Fill the system with dry nitrogen through the other service valve
gauge port and then turn the nitrogen flow off just before brazing is begun.
Protect the TXV, copper to aluminum suction header joint, and outdoor unit service
valves from overheating using a wet rag or heat sink compound. Leave the wet rag or
heat sink material in place until the joint and surrounding tubing cools down to a safe
temperature. Double tip torches can help minimize brazing time and heat conduction to
the heat sensitive components if the flame is turned down and held on the joint just long
enough to make the braze joint. With both single and double tip torches, turning the
flame up too much and keeping the flame on the joint too long will damage the heat sen-
sitive components even when a wet rag or heat sink compound is used.
Use a sheet metal shield to protect the cabinet’s paint from the torch flames during the braz-
ing process. The vapor line insulation should be pushed back on the line about 12 inches
from the joint and retained to prevent it from igniting or melting during the brazing process.
After the refrigerant brazed connections are made at the air-handler and the tubing has
cooled down sufficiently, replace the coil section access panel if it has been removed
and seal the air gap around the connection stubs with the foam rubber gasket included
in the air-handler parts bag. Peel the self-adhesive backing off of the foam gasket and
position it around the stubs with the adhesive side toward the cabinet, then press it firm-
ly against the cabinet. The gasket is split to allow it to go over the stubs after the refrig-
erant tubes are brazed to the stubs. (See Figure 11 in Section 3.10)
After the foam gasket has been installed, the vapor line insulation should be pulled back
in place so it contacts the air-handler cabinet to prevent condensate from forming on the
cold tube and dripping off. A loosely fitting zip-tie placed around the insulation ½” from
the end can be used to hold it in place so it doesn’t move away from the cabinet. For air-
handlers with TXV’s, a section of the insulation will need to be cut out to make room for
the externally mounted TXV bulb.
(See Section 3.10)
Once the bulb is mounted, insu-
late the bulb with the foam insulation included in the air-handler parts bag, making sure
none of the vapor line is uninsulated.
2417
1
1
⁄
2
Ton
R-410A
.049
2 Ton
.057*
3617
2
1
⁄
2
Ton
R-410A
.062
3 Ton
.067*
4821
3
1
⁄
2
Ton
R-410A
.074
4 Ton
.078*
Indoor
Nominal Tons
Refrigerant
Piston
