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Chapter 5 Troubleshooting
50 CNT-APG002-EN
Example 3
The technician experiences the same problem as in the first two exam-
ples: a hot-water valve cycles closed every few minutes, and the dis-
charge-air temperature swings across a range of 10°F (5.6°C). The
technician graphs the discharge-air temperature setpoint and the hot-
water valve position, as shown in Figure 35.
Figure 35: Hot-water valve position, gains too high
The dramatic changes in the hot-water valve position indicate that the
gains are too high. The technician reduces the proportional gain from 16
to 1 and the integral gain from 4 to 0.25. This stops the hot-water valve
from cycling but increases the time to reach setpoint to more than 20 min-
utes. The technician then increases the proportional gain to 4 and the
integral gain to 1, which brings the discharge-air temperature to setpoint
more quickly while still preventing the hot-water valve from cycling.
Time (minutes)
Discharge-air
temperature setpoint (°F)
Discharge-air
temperature (°F)
Hot-water valve
position (%)
Discharge-air temperature and valve position