Communication Failures; Comm Failure1 - Upc To Len Fail; Comm Failure2 - Upc To Excb Fail; On-Board Pressure Transducers - Carrier 48HC 04-28 Controls, Start-Up, Operation And Troubleshooting

Communication Failures

Communication is critical for ERV operation. It can fail on two
different paths; between the UPC and the rooftop (LEN), or be-
tween the UPC and the EXCB. This makes the UPC critical to
ERV operation. Make sure the UPC DIP switches and rotary
switches are set correctly. Make sure the board hardware jumpers
are set on EIA 485 and 2W. During normal operation the 4 com-
munication LEDs will flash interchangeably. If all 4 LEDs are not
flashing then there is a communication problem. Check connec-
tions between Port 1a and rooftop's LEN connection and Port 2
and the EXCB J23 (verify with the proper unit schematic).
The ERVs, LCD screen will show specific communication fail-
ures when they occur. Use the LCD screen to help troubleshoot
communications failures. If communication is established, the
LED shows "communication connected".
COMM FAILURE1 – UPC TO LEN FAIL
This will be displayed if the EXCB can communicate with the
UPC, but the UPC does not receive information from the Com-
fortLink controller. This will occur if the cable is pinched or
disconnected, wired wrong or loose, or if the UPC is config-
ured wrong.
COMM FAILURE2 – UPC TO EXCB FAIL
This will be displayed if the EXCB cannot communicate with
the UPC. This will occur if the connection between them is dis-
connected or pinched. This will also occur if the UPC does not
have power or software, or if it has an error or configured
wrong.

On-Board Pressure Transducers

The EXCB uses on-board pressure transducers to measure the
air pressure of the incoming outside air and the building ex-
haust air. The CFM values are then calculated based on these
readings and the fan speed. There is a pressure transducer for
the outside air and one for the exhaust air. These are screwed
into the EXCB board to J24 and J25 respectively. They have
three pins: IN, GND, and OUT. The IN pin is 5vdc input power
and GND is the common or ground pin. The OUT pin will be
0.26 to 4.5vdc based on the pressure reading. There are two
different transducers used, two inch of water column (in.wg)
and 5 in.wg. Table 28 shows the voltage/pressure characteris-
tics of each.
Table 28 — Transducer/Voltage vs. Pressure
Voltage (vDC)
<= –0.26
0.5
1.0
1.5
2.0
2.5
3.0
3.5
4.0
4.5

MAJOR SYSTEM COMPONENTS

General

The 48/50HC single package rooftop units contain the Com-
fortLink electronic control system that monitors all operations of
the rooftop. The control system is composed of several main con-
trol components and available factory-installed options or field-in-
stalled accessories as listed in sections below. See Figs. 24-31 for
typical control and power schematics for 48HC and 50HC. Refer
to the base unit installation instructions or actual unit control box
for specific unit wiring diagrams.
68
Pressure (in.wg)
2 in. transducer 5 in. transducer
0.00 0.00
0.12 0.28
0.34 0.87
0.53 1.46
0.82 2.05
1.06 2.64
1.30 3.23
1.52 3.82
1.76 4.41
2.00 5.00