SERVICING
14
NETWORK TROUBLESHOOTING
Communications is achieved by taking the difference
between a positive dc signal and a negative dc signal. The
positive dc signal is termed “data 1” or “1”. Data 1 is positive
with respect to ground (or common). The negative dc signal
is termed “data 2” or “2”. Data 2 is negative with respect
to ground (or common). Data 1 should be approximately
2.8 volts dc. Data 2 should be approximately 2.2 volts dc.
The voltage difference between data 1 and data 2 should
be approximately 0.6 volts dc. Verify that the bus DS1 dip
switches are in the ON position.
The integrated air handler control has some on-board tools
that may be used to troubleshoot the network. These tools
are: red communications LED, green receive (Rx) LED, and
learn button. These are described below
a. Red communications LED – Indicates the status
of the network. Refer to the Network Trouble-
shooting Chart for the LED status and the corre-
sponding potential problem.
b.
Green receive LED – Indicates network traffic.
Refer to the Network Troubleshooting Chart for
the LED status and the corresponding potential
problem.
c. Learn button – Used to reset the network. De-
press the button for approximately 2 seconds to
reset the network.
Voltages between the two data lines and between each
data line and common may be used to determine if the
network is operating properly.
Do the following to measure the voltages on the communi-
cations data lines.
WARNING
Line voltage now present.
1. With power on to the unit, measure voltage between
terminal “1” and terminal “C” on control board’s ther-
mostat connector. Voltage should be as noted in the
table below.
2. Measure voltage between terminals “2” and “C”.
3. Measure voltage between terminals “1” and “2”.
4.
If voltages are different than stated in the table below,
check thermostat wiring for opens/shorts.
5. The network troubleshooting chart provides additional
communications troubleshooting information.
Terminals
Nonimal dc
Voltages
1 to C
> 2.5 Vdc
2 to C
< 2.5 Vdc
1 to 2
> 0.2 Vdc
REFRIGERATION REPAIR PRACTICE
DANGER
Always remove the refrigerant charge in a proper manner
before applying heat to the system.
When repairing the refrigeration system:
WARNING
HIGH VOLTAGE
Disconnect ALL power before servicing or in-
stalling this unit. Multiple power sources may
be present. Failure to do so may cause proper-
ty damage, personal injury or death.
1. Never open a system that is under vacuum. Air and
moisture will be drawn in.
2. Plug or cap all openings.
3. Remove all burrs and clean the brazing surfaces of
the tubing with sand cloth or paper. Brazing materials
do not flow well on oxidized or oily surfaces.
4. Clean the inside of all new tubing to remove oils and
pipe chips.
5. When brazing, sweep the tubing with dry nitrogen to
prevent the formation of oxides on the inside surfaces.
6. Complete any repair by replacing the liquid line drier
in the system, evacuate and charge.
BRAZING MATERIALS
IMPORTANT NOTE:
Torch heat required to braze tubes of
various sizes is proportional to the size of the tube. Tubes
of smaller size require less heat to bring the tube to brazing
temperature before adding brazing alloy. Applying too much
heat to any tube can melt the tube. Service personnel must
use the appropriate heat level for the size of the tube being
brazed.
NOTE:
The use of a heat shield when brazing is recom-
mended to avoid burning the serial plate or the finish on the
unit. Heat trap or wet rags should be used to protect heat
sensitive components such as stop valves, EEV, TXV and
filters.
Copper to Copper Joints - Sil-Fos used without flux (alloy
of 15% silver, 80% copper, and 5% phosphorous). Recom-
mended heat 1400°F.
Copper to Steel Joints - Silver Solder used without a flux
(alloy of 30% silver, 38% copper, 32% zinc). Recommended
heat - 1200°F.
