Terminal Unit
Control (TUC)
102 UNT-IOM-6
Use the human interface to read the unit operating machine state.
1. Read and record the initial TUC address.
2. Set the TUC DIP switch #5 and #8 to ON (address = 9). The
remaining switches will be off.
3. Short and hold the test input.
4. The LEDs will blink to define an operating machine state. The
operating machine state information will be displayed in a series
of three blink sequences.
Sequence 1: When the test input is shorted continuously all
LEDs go off for one second.
Sequence 2: LED #5 will light to indicate that sequence 2 is
currently being displayed. LEDs one through four will display the
first part of the operating machine state.
Sequence 3: LED #6 will light to indicate that sequence 3 is
currently being displayed. LEDs one through four will display the
second part of the operating machine state.
5. Reference Table 25 on page 75 to interpret the operating machine
state derived from the blink sequences.
Table 40. Blink Sequence Corresponding Diagnostic Codes
Sequence 1 Sequence 2 Sequence 3
1 2 3 4 1 2 3 4 1 2 3 4 Code Diagnostic Latch
None Power failure None
None Controller failure None
00 None N/A
8B Condensate overflow Yes
9B Leaving water temp No
sensor 1 failure
A0 Zone and supply temp No
sensor failure
C8 High EWT No
CB Low EWT No
CF Low temp. detect. or Yes
condensate overflow
D3 Low discharge air temp Yes
D4 Smoke alarm Yes/No
D5 High dischg air temp Yes/No
DD Low fresh air temp No
F8 Bad configuration No
FE Return air high limit Yes
Reading the
Operating
Machine State
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