Economizer; Economizer Fault Detection And - Carrier 48HC 04-28 Controls, Start-Up, Operation And Troubleshooting

time are displayed as Available Heating Stages (Run Sta-
 
tus HEAT AVL.H). The actual heat relays on at any given
time are displayed as Actual Heating Stages (Operating
 
Modes HEAT ACT.H). Heat Stage 1 Relay (Run Sta-
 
tus HEAT HT.1) and Heat Stage 2 Relay (Run Sta-
 
tus HEAT HT.2) are displayed on when the respective relay
is energized. There are time guards to protect from short cycling,
Heat Minimum On Time (Configuration
and Heat Minimum
 
tion HEAT MOT.H) apply before a heat relay can be turned
back on or turned off.
Integrated Gas Controller (IGC)
The heat staging is determined as described above and the Inte-
grated Gas Controller (IGC) initiates the gas heat module start-
up. The Integrated Gas Controller (IGC) minimum on-time of
1 minute will be followed even if Heat Minimum On Time
 
(Configuration HEAT MRT.H) is lower and during Ser-
vice Test. If the IGC temperature limit switch opens within 10
minutes of the end of the gas heat cycle, the next fan off delay
will be extended by 15 seconds. The maximum delay is 3 min-
utes. Once modified by the IGC, the fan off delay will not
change back to the configured Fan-off Delay, Gas Heat (Con-
 
figuration HEAT FOD.G) unless power is reset to the con-
trol. A light emitting diode (LED) is provided on the IGC to in-
dicate status. During normal operation the LED is continuously
on. See the Troubleshooting section if the LED is off or flash-
ing. The IGC is located behind the gas section access panel
door.
When the control energizes Heat Stage 1 Relay (Run Sta-
 
tus HEAT HT.1), power is sent to the W terminal on the
IGC board. A check is made to ensure that the rollout switch
and limit switch are closed. The induced-draft motor is then
energized, and when speed is proven with the Hall Effect sen-
sor on the motor, the ignition activation period begins. The
burners will ignite within 5 seconds. If the burners do not light,
there is a 22-second delay before another 5-second attempt. If
the burners still do not light, this sequence is repeated for 15
minutes. After the 15 minutes have elapsed, if the burners still
have not lit, heating is locked out. The control will reset when
the request for heat is temporarily removed. When ignition oc-
curs, the IGC board will continue to monitor the condition of
the rollout switch, limit switches, the Hall Effect sensor, as
well as the flame sensor. If the unit is controlled through a
room thermostat or space sensor set for fan auto, 45 seconds
after ignition occurs the indoor-fan motor will be energized
(and the outdoor-air dampers will open to their minimum posi-
tion). If for some reason the over temperature limit opens prior
to the start of the indoor fan blower, on the next attempt, the
45-second delay will be shortened to 5 seconds less than the
time from initiation of heat to when the limit tripped. Gas will
not be interrupted to the burners and heating will continue.
Once modified, the fan on delay will not change back to 45
seconds unless power is reset to the control. When the control
energizes Heat Stage 2 Relay (Run Status
power is supplied to the second stage of the main gas valve. If
both stage 1 and stage 2 of the gas valve close, gas will be
turned off to the main burners.

Economizer

If an economizer is installed, then Economizer Installed (Con-
 
figuration ECON EC.EN) should be set to YES. The
economizer damper is controlled by the Econo Commanded

Position (Configuration ECON
er Control Board (ECB). Feed back from the economizer actu-
ator is output to the ECB and is displayed as Econo Actual Po-
 
sition (Outputs ECON
 
HEAT MRT.H)
Off Time (Configura-
 
HEAT

EC.CP) on the Economiz-
EC.AP). The Economizer is used
for ventilation, cooling and to control the power exhaust. If the
Indoor fan is not on, the economizer will not operate.
ECONOMIZER FAULT DETECTION AND DIAGNOSTICS
(FDD) CONTROL
The Economizer Fault Detection and Diagnostics control can
be divided into two tests:
1. Test for mechanically disconnected actuator
2. Test for stuck/jammed actuator
1. Mechanically Disconnected Actuator
The test for a mechanically disconnected actuator shall be per-
formed by monitoring SAT as the actuator position changes
and the damper blades modulate. As the damper opens, it is ex-
pected SAT will drop and approach OAT when the damper is at
100%. As the damper closes, it is expected SAT will rise and
approach RAT when the damper is at 0%. The basic test shall
be as follows:
1. With supply fan running take a sample of SAT at current
actuator position.
2. Modulate actuator to new position.
3. Allow time for SAT to stabilize at new position.
4. Take sample of SAT at new actuator position and deter-
mine:
a. If damper has opened, SAT should have decreased.
b. If damper has closed, SAT should have increased.
5. Use current SAT and actuator position as samples for next
comparison after next actuator move.
The control shall test for a mechanically disconnected damper
if all the following conditions are true:
1. An economizer is installed.
2. The supply fan is running.
3. Conditions are good for economizing.
4. The difference between RAT and OAT > T24RATDF. It is
necessary for there to be a large enough difference
between RAT and OAT in order to measure a change in
SAT as the damper modulates.
5. The actuator has moved at least T24ECSTS %. A very
small change in damper position may result in a very small
(or non-measurable) change in SAT.
6. At least part of the economizer movement is within the
range T24TSTMN% to T24TSTMX%. Because the mix-
ing of outside air and return air is not linear over the entire
range of damper position, near the ends of the range even a
large change in damper position may result in a very small
(or non-measurable) change in SAT.
Furthermore, the control shall test for a mechanically discon-
nected actuator after T24CHDLY minutes have expired when
any of the following occur (this is to allow the heat/cool cycle
to dissipate and not influence SAT):
HT.2),
1. The supply fans switches from OFF to ON.
2. Mechanical cooling switches from ON to OFF.
3. Reheat switches from ON to OFF.
4. The SAT sensor has been relocated downstream of the
heating section and heat switches from ON to OFF.
The economizer shall be considered moving if the reported po-
sition has changed at least ± T24ECMDB %. A very small
changed in position shall not be considered movement.
The determination of whether the economizer is mechanically
disconnected shall occur SAT_SEC/2 seconds after the econo-
mizer has stopped moving.
23