Pressure Switch Stuck Open
A pressure switch stuck open can be caused by a faulty pres- sure switch, faulty wiring, a disconnected or damaged hose, a blocked or restricted flue, or a faulty induced draft blower.
If the control senses an open pressure switch during the pre- purge cycle, the induced draft blower only will be energized. If the pressure switch opens after ignition has begun the gas valve is deenergized, the circulator blower heat off cycle be- gins, and the induced draft blower remains on. The diagnos- tic fault code is two flashes.
Pressure Switch Stuck Closed
A stuck closed pressure switch can be caused by a faulty pressure switch or faulty wiring. If the control encounters a pressure switch stuck closed, the induced draft blower re- mains off. The diagnostic LED code for this fault is three (3) flashes.
Open Thermal Protection Device
If the primary limit switch opens, the gas valve is immediately deenergized, the induced draft and air circulating blowers are energized. The induced draft and air circulator blowers remain energized until the limit switch recloses. The diag- nostic fault code for an open limit is four (4) flashes.
A primary limit will open due to excessive supply air tempera- tures. This can be caused by a dirty filter, excessive duct
INPUT RATING
It is the responsibility of the contractor to adjust the gas input to the unit. The input rate can be calculated by using the formula:
INPUT Btu/Hr = | 3600 x HV | |
T | ||
|
WHERE:
HV = Heating value of fuel = Btu/ft3 of gas
T = Time in seconds per ft3 of gas flow as read from gas meter
Adjust input rate by varying the adjustment of the gas pres- sure regulator on the gas valve. All adjustments must be made with furnace operating at high fire and at normal operating temperature. Clockwise (P) rotation of the pressure regula- tor screw increases pressure and gas flow rate. Turn screw counterclockwise (Q) to decrease pressure and gas flow rate. After adjustment the furnace temperature rise must be within the range specified on the unit data plate. NOTE: Thermal efficiency of the furnace is a product efficiency rating deter- mined under continuous operating conditions independent of any installed system.
Outlet Pressure | Pressure Regulator | |
Adjustment | ||
Tap | ||
(Under Cap Screw) |
static, insufficient air flow, or a faulty limit. Check filters, total external duct static, blower motor, blower motor speed tap (see wiring diagram), and limit. This limit will automatically reset once the temperature falls below a preset level.
Flame Detected with Gas Valve Closed
If flame is detected with the gas valve deenergized, the com- bustion and air circulator blowers are energized. The diag- nostic fault code is five (5) flashes for this condition. The control can be reset by removing the power supply to the unit
INLET
Inlet Pressure |
Tap |
OUTLET
Gas Valve
On/Off
Selector
Switch
or it will automatically reset after one hour. Miswiring is the probable cause for this fault.
ABNORMAL OPERATION - COOLING
Short Cycle Compressor Delay
Open to | Manometer |
|
|
Atmosphere | Hose |
|
|
|
|
| |
|
| High Fire Regulator |
|
| Outlet | Adjust | Regulator |
| Pressure Boss |
| Vent |
The automatic ignition control has a
NOTE: Some electronic thermostats also have a
Inlet |
Pressure Boss |
Manometer
Low Fire
Regulator Adjust
thermostat and the compressor has not started after three minutes, wait an additional five minutes to allow the thermostat to complete its short cycle delay time.
Pressure Adjustments
21
