Carrier FA4ANF Service Manual

The time required for PTC to heat to a sufficient point controls ONtiming of device. The time required for disc to cool down whenpower is removed controls OFF time of device. The PTC can bevaried to provide varied timing. Typically a short ON equates to along OFF.Because this is a thermally-activated device, ambient conditionsaffect the ON/OFF cycle. Higher ambient temperature meansshorter ON times and longer OFF times.These sequencers may be "ganged up" to 3 on a common mountingplate to control up to 6 heater elements. In this situation, PTCs aredifferent in each sequencer to provide a staged ON of a minimumof 10 sec between each sequencer — 3 stages of 2 elements sincethe KFA and KFB series heaters use sequencers in which bothswitches of the 2-pole sequencer close simultaneously. Oldermodels used sequencers which had a minimum delay of 10 secbetween each switch.Application of these devices is such that the first switch ON notonly turns on first heater element, but also ensures that indoor fanis energized, because first ON is last OFF. This ensures fanremains ON until the last heater de-energizes.KFC AND KFD ELECTRIC HEAT RELAYKFC and KFD electric heater packages have relays controlling theheater elements instead of sequencers. A small rectifier PCB ismounted to each relay which converts the incoming 24-vac controlsignal to dc. In addition to the rectifier circuit, the second and thirdstage relays contain a time-on delay circuit of 5 seconds for secondstage, and 8 seconds for third stage. When the control signal isremoved from the relays, all relays will open with no time-offdelay.Step 2—Troubleshooting KFA, KFB, KFC, and KFDSeries Electric HeatersDISCOLORED WIRE INSULATION AT TERMINALCheck quick-connect terminal at discoloration. Connection may beloose, creating a high resistance through connection point.FUSE FAILURE1. Check for shorted wire. Replace wire. Never try to fix wireusing electrical tape.2. Check shorted element. If element is shorted, replace heater.NO HEAT1. Check fuse for failure. If fuse has failed, refer to Fuse Failuresection.2. Check for faulty transformer. Check output voltage of trans-former secondary side R (red) and C (brown). Make sureoutput is between 18 and 30 vac. If output voltage is low andinput voltage tests normal, replace transformer.3. Check for miswired heater plug harness.4. Check limit switch or sequencer failure. These switchesshould have failed in open position. If output voltage is zerovolts, replace switch.5. Check heater relay and PCB (KFC and KFD heaters only).Control voltage input to PCB should be 24-vac. Output torelay should be 18-vdc minimum. If input is present but nooutput, replace PCB. If output is present, replace relay.HEATER WILL NOT TURN OFF1. Check low-voltage wiring for miswire.2. Check for shorted elements to ground.3. Replace sequencer/relays. They may be stuck closed.NUISANCE TRIPS1. Check for low airflow due to dirty filters, blocked registers, orundersized duct.2. Check blower motor and wheel for proper operation. Exces-sive current draw of motor will cause internal overload to trip.3. The fan speed may be low.FAN COIL DESCRIPTIONAND TROUBLESHOOTINGFK4BThe FK4B is similar to the discontinued FK4A as they have bothintegrated controls and motor (ICM) and their own special circuitboard. The greatest difference between the 2 models is the wayeach goes about delivering air.Setting up desired airflow on the FK4B is obtained by theselections made on Easy Select™ circuit board. The motor deliversrequested airflow as defined by signals received from Easy SelectBoard and its internal programming. The major difference is thatthe FK4B motor reacts to changes in system static pressures tomaintain constant airflow.Unlike conventional fan coils where static pressure affects airflow,the FK4B is a constant airflow unit. The blower delivers requestedairflow up to about 0.7 in. of static pressure. The ICM2 ispre-programmed and contains airflows for all modes of operation.Blower characteristics (airflow, torque, and speed-vs-static pres-sure) are known from laboratory testing. If any 3 characteristics areknown, the fourth is defined.Requested airflow is known because of Easy Select board con-figuration and thermostat signals. Torque is known because it isdirectly related to armature current which is measured by motorcontrol. Speed is measured from its generated back EMF. Thisinformation is entered into an expression which calculates torquefrom speed and airflow numbers. If calculation does not matchstored blower characteristics, torque is adjusted every 0.8 sec untilagreement is reached. The unit does not directly measure staticpressure, but does react to a change in static to maintain constantairflow.Step 1—Integrated Controls and Motor (ICM2)The ICM2 is similar to the ICM1 used in FK4A series units, butcannot be used as a replacement without some modification toFK4A unit. Consult SMB 93-0052 for motor conversion kit. Theelectronics of motor are built into rear of motor, deriving the nameICM. (See Fig. 15.)An ICM is first fed high voltage AC power through the 5-pinconnector. The AC power is then rectified to DC by a diodemodule. After rectification, DC signal is electronically communi-cated and fed in sequential order to 3 stator windings. Thefrequency of communication pulses determines motor speed. Therotor is permanently magnetized.An ICM is powered with high voltage at all times. The motor willnot run with high voltage alone. Low voltage must be applied tocontrol plug to run motor.Step 2—PCB Layout and DescriptionNOTE: Layout of actual PCB is depicted in Fig. 16 and 17.The control is a single PCB which interfaces a variable-speedICM2 with other system components.Power for system is supplied from a 230-vac, 60-Hz line. Class 2voltage (24 vac nom.), used for thermostat connections, is derivedfrom a transformer located in close proximity to control. Theprimary and secondary of transformer are connected to controlboard. The 24-vac secondary circuit includes a socket, solderedinto circuit at SEC2, to receive a 5-amp automotive-type fuse.20