Burner Ignition; Orifice Replacement - Carrier 48FC M20 Series Service And Maintenance Instructions

GAS VALVE
All three-phase models are equipped with 2-stage gas valves.
See Fig. 56 for locations of adjustment screws and features on
the gas valve.
ON/OFF
SWITCH
NPT INLET
INLET
PRESSURE
TAP
NPT OUTLET
2 STAGE
Fig. 56 — Typical 2 Stage Gas Valve
To adjust gas valve pressure settings:
IMPORTANT: Leak check all gas connections including the
main service connection, gas valve, gas spuds, and manifold
pipe plug. All leaks must be repaired before firing unit.
CHECK UNIT OPERATION AND MAKE NECESSARY
ADJUSTMENTS
NOTE: Gas supply pressure at gas valve inlet must be within
specified ranges for fuel type and unit size. For natural gas see
Tables 5 and 6. For liquid propane see Tables 7 and 8.
1. Slide out the burner partition panel.
2. Remove manifold pressure tap plug from manifold and con-
nect pressure gauge or manometer. (See Fig. 52.)
3. Turn on electrical supply.
4. Turn on unit main gas valve.
5. Set room thermostat to call for heat. If unit has two-stage gas
valve, verify high-stage heat operation before attempting to
adjust manifold pressure.
6. When main burners ignite, check all fittings, manifold, and
orifices for leaks.
7. Adjust high-stage pressure to specified setting by turning the
plastic adjustment screw clockwise to increase pressure,
counter-clockwise to decrease pressure.
8. For two-stage gas valves, set room thermostat to call for low-
stage heat. Adjust low-stage pressure to specified setting.
9. Replace regulator cover screw(s) when finished.
10. Observe unit heating operation in both high stage and low
stage operation if so equipped. Observe burner flames to see
if they are blue in appearance, and that the flames are approx-
imately the same for each burner.
11. Turn off unit, remove pressure manometer and replace the
manifold pressure tap plug. (See Fig. 52.)
REGULATOR
COVER SCREW (2)
PLASTIC ADJUST
SCREW (2)
REGULATOR SPRING (2)
(PROPANE - WHITE
NATURAL - SILVER)
LOW STAGE
GAS PRESSURE
REGULATOR
ADJUSTMENT
MANIFOLD
PRESSURE TAP
42
LIMIT SWITCH
Remove the indoor blower access panel. Limit switch is located
on the heat exchanger cover panel. See Fig. 51.

Burner Ignition

Unit is equipped with a direct spark ignition 100% lockout system.
The Integrated Gas Unit Controller (IGC) is located in the control
box (see Fig. 54). The IGC contains a self-diagnostic LED (light-
emitting diode). A single LED (see Fig. 57) on the IGC provides a
visual display of operational or sequential problems when the
power supply is uninterrupted. When a break in power occurs, the
IGC will be reset (resulting in a loss of fault history) and the in-
door (evaporator) fan ON/OFF times will be reset. The LED error
code can be observed through the viewport. During servicing, re-
fer to the label on the control box cover or Table 9 for an explana-
tion of LED error code descriptions.
If lockout occurs, unit may be reset by interrupting power supply
to unit for at least 5 seconds.
Table 9 — LED Error Code Descriptions
LED INDICATION
ON
OFF
1 Flash b Evaporator Fan On/Off Delay Modified
2 Flashes
3 Flashes
4 Flashes
5 Flashes
6 Flashes
7 Flashes
8 Flashes
9 Flashes
NOTE(S):
a. A 3-second pause exists between LED error code flashes. If more than one er-
ror code exists, all applicable codes will be displayed in numerical sequence.
b. Indicates a code that is not an error. The unit will continue to operate when this
code is displayed.
LEGEND
LED — Light Emitting Diode
IMPORTANT: Refer to Tables 10 and 11 for additional
troubleshooting information.

Orifice Replacement

This unit uses orifice type LH32RFnnn (where "nnn" indicates
orifice reference size). When replacing unit orifices, order the
necessary parts through RCD. See the High Altitude Gas Con-
version Kit Gas Heating/Electric Cooling 3-15 Ton Small
Rooftop Units Accessory LP (Liquid Propane) Installation In-
structions for details.
Ensure each replacement orifice is tight as its threads into the
manifold pipe and the orifice projection does not exceed maxi-
mum value. See Fig. 50.
a
ERROR CODE DESCRIPTION
Normal Operation
Hardware Failure
Limit Switch Fault
Flame Sense Fault
4 Consecutive Limit Switch Faults
Ignition Lockout Fault
Induced-Draft Motor Fault/
Pressure Switch Fault
Rollout Switch Fault
Internal Control Fault
Software Lockout