York ZF180 Installation Manual

Also see for ZF 180 Series: Technical guide Installation manual Instruction manual Technical guide Installation manual

Contents

5168276-XIM-B-0216Johnson Controls Unitary Products 41This limit is monitored regardless of unit operation status, i.e.this limit is monitored at all times.If the temperature limit opens three times within one hour, it willlock-on the indoor blower motor and flash code is initiated (SeeTable 31).Gas ValveThe UCB continuously monitors the GV. Any time the UCBsenses voltage at the GV without a call for heat for a continuousfive-minute period, the UCB will lock-on the indoor blower and aflash code is initiated (Table 31). When voltage is no longersensed at the GV, the UCB will de-energize the indoor blowerfollowing the elapse of the fan off delay for heating.If voltage has been sensed at the GV for at least 15 secondsduring the fan on delay for heating and GV voltage or “W1” islost, the indoor blower is forced on for the length of the fan offdelay for heating.Safety ControlsThe UCB monitors the temperature limit switch of gas heat units.The control circuit includes the following safety controls:Limit Switch (LS)This control is located inside the gas heat compartment and isset to open at the temperature indicated in the Gas Heat LimitControl Settings Table 27. It resets automatically. The limitswitch operates when a high temperature condition, caused byinadequate supply air flow occurs, thus shutting down theheater and energizing the blower.Auxiliary Limit Switch (AUX)This control is located inside the heat exchanger compartmentand is set to open at 190°F. It is a manual reset switch. If AUXtrips, then the primary limit has not functioned correctly.Replace the primary limit.NOTE: Access to (LS) and (AUX) switches is through thecompressor access panel on side dischargeapplications and through the discharge air duct coveron down discharge applications.Figure 25: Gas Heat Limit And Auxiliary Location DownDischarge ApplicationFigure 26: Gas Heat Limit and Auxiliary Location SideDischarge ApplicationCentrifugal Switch (CS)If the draft motor should fail, the centrifugal switch attached tothe shaft of the motor prevents the ignition controls and gasvalves from being energized.Redundant Gas ValveThere are two separate gas valves in the furnace. Each valvecontains a main and a redundant valve. The redundant valvesare located upstream of the main gas valves. Should either orboth of the main gas valves fail in the open position theredundant valves serve as back-ups and shut off the flow of gas.Flame Sensor Rod / 100% Ignition Control Lock-Out.The flame rods and controls are located per Proper FlameAdjustment Figure 28. If an ignition control fails to detect aAuxilaryLimitLimitSwitchLimitAccess