Controls, Start-Up, Operation, Service and ... - Climayoreo

Limit Switch Temperature Monitoring (LIM.M) — Variable
air volume applications in the low heat or tempering mode can
experience low airflow and as a result it is possible for nuisance
trips of the gas heat limit switch, thereby shutting off all gas
stages. In order to achieve consistent heating in a tempering
mode, a thermistor (TemperaturesAIR.TS.G.LS) is placed
next to the limit switch and monitored for overheating. In order
to control a tempering application where the limit switch
temperature has risen above either the upper or lower configuration
parameters (SW.L.T, SW.H.T), the staged gas control
will respond by clamping or droping gas stages.
If the Limit Switch Monitoring configuration parameter
(LIM.M) is set to YES, all the modes will be monitored. If set
to NO, then only LAT Cutoff mode and Capacity Clamp mode
for RISE will be monitored.
If S.G.LS rises above SW.L.T or if (LAT – LAT last time
through the capacity calculation) is greater than (RISE)
degrees F per second, the control will not allow the capacity
routine to add stages and will turn on the Capacity Clamp
mode.
If S.G.LS rises above SW.H.T the control will run the capacity
routine immediately and drop all heat stages and will turn
on the Limiting mode.
If S.G.LS falls below SW.L.T the control will turn off both
Capacity Clamp mode and Limiting mode with one exception.
If (LAT – LAT last time through the capacity calculation) is
greater than “RISE” degrees F per second, the control will stay
in the Capacity Clamp mode.
If control is in the Limiting mode and then S.G.LS falls
below SW.L.T, and LAT is not rising quickly, the control will
run the capacity calculation routine immediately and allow a
full stage to come back on if desired this first time through
upon recovery. This will effectively override the “max capacity
stage” clamp.
In addition to the above checks, it is also possible at low cfm
for the supply-air temperature to rise and fall radically between
capacity calculations, thereby impacting the limit switch temperature.
In the case where supply-air temperature (LAT) rises
above the control point (HT.C.P) + the cutoff point (LAT.L) the
control will run the capacity calculation routine immediately
and drop a stage of heat. Thereafter, every time the capacity
calculation routine runs, provided the control is still in the LAT
cutoff mode condition, a stage will drop each time through.
Falling back below the cutoff point will turn off the LAT cutoff
mode.
STAGE
Table 46 — Staged Gas Heat Control Steps (HT.ST = 0)
Table 47 — Staged Gas Heat Control Steps (HT.ST = 1)
62
INTEGRATED GAS CONTROL BOARD LOGIC — All gas
heat units are equipped with one or more integrated gas control
(IGC) boards. This board provides control for the ignition system
for the gas heat sections.
On size 030-050 low heat units there will be one IGC board.
On size 030-050 high heat units and 055-100 low heat units
there are two IGC boards. On size 055-100 high heat units
there are three IGC boards.
When a call for gas heat is initiated, power is sent to W on
the IGC boards. For standard 2-stage heat, all boards are wired
in parallel. For staged gas heat, each board is controlled separately.
When energized, an LED on the IGC board will be
turned on. See Table 49 for LED explanations.
Each board will ensure that the rollout switch and limit
switch are closed. The induced-draft motor is then energized.
When the speed of the motor is proven with the Hall Effect
sensor on the motor, the ignition activation period begins. The
burners ignite within 5 seconds. If the burners do not light,
there is a 22-second delay before another 5-second attempt is
made. If the burners still do not light, this sequence is repeated
for 15 minutes. After 15 minutes have elapsed and the burners
have not ignited then heating is locked out. The control will reset
when the request for W (heat) is temporarily removed.
When ignition occurs, the IGC board will continue to monitor
the condition of the rollout switch, limit switches, Hall Effect
sensor, and the flame sensor. Forty-five seconds after ignition
has occurred, the IGC will request that the indoor fan be
turned on.
The IGC fan output (IFO) is connected to the indoor fan input
on the MBB which will indicate to the controls that the indoor
fan should be turned on (if not already on). If for some
reason the overtemperature limit switch trips prior to the start
of the indoor fan blower, on the next attempt the 45-second delay
will be shortened by 5 seconds. Gas will not be interrupted
to the burners and heating will continue. Once modified, the
fan delay will not change back to 45 seconds unless power is
reset to the control.
Table 45 — Staged Gas Heat
NUMBER OF
STAGES
HT.ST
CONFIGURATION
UNIT SIZE
48P
HEAT SIZE
2 0 030-050 Low
5 1
030-050
055-100
High
Low
9 3 055-100 High
RELAY OUTPUT
Heat 1 Heat 2 Heat 3 Heat 4 Heat 5 Heat 6
MBB-RLY8 MBB-RLY7 SCB-RLY1 SCB-RLY2 SCB-RLY3 SCB-RLY4
IGC1 MGV1 IGC2 MGV2 IGC3 MGV3
CAPACITY
%
0 OFF OFF OFF OFF OFF OFF 0
1 ON OFF OFF OFF OFF OFF 75
2 ON ON OFF OFF OFF OFF 100
STAGE
RELAY OUTPUT
Heat 1 Heat 2 Heat 3 Heat 4 Heat 5 Heat 6
MBB-RLY8 MBB-RLY7 SCB-RLY1 SCB-RLY2 SCB-RLY3 SCB-RLY4
IGC1 MGV1 IGC2 MGV2 IGC3 MGV3
CAPACITY
%
0 OFF OFF OFF OFF OFF OFF 0
1 ON OFF OFF OFF OFF OFF 37
2 ON ON OFF OFF OFF OFF 50
3 ON OFF ON OFF OFF OFF 75
4 ON ON ON OFF OFF OFF 87
5 ON ON ON ON OFF OFF 100