Carrier Residential Air Conditioners and Heat Pumps Application Manualline

Also see for 24ANB124: Installation instructions

Carrier Residential Air Conditioners and Heat Pumps Application Manualline Manual pdf 12 page image

12Use following formula to calculate capacitance:Capacitance (mfd)= (2650 X amps)/volts3. Remove any capacitor that shows signs of bulging, dents, orleaking. Do not apply power to a defective capacitor as itmay explode.Sometimes under adverse conditions, a standard run capacitor in asystem is inadequate to start compressor. In these instances, a startassist device is used to provide an extra starting boost tocompressor motor. This device is called a positive temperaturecoefficient (PTC) or start thermistor. It is a resistor wired in parallelwith the run capacitor. As current flows through the PTC atstart--up, it heats up. As PTC heats up, its resistance increasesgreatly until it effectively lowers the current through itself to anextremely low value. This, in effect, removes the PTC from thecircuit.After system shutdown, resistor cools and resistance value returnsto normal until next time system starts. Thermistor device isadequate for most conditions, however, in systems where off cycleis short, device cannot fully cool and becomes less effective as astart device. It is an easy device to troubleshoot. Shut off all powerto system.Check thermistor with ohmmeter as described below. Shut off allpower to unit. Remove PTC from unit. Wait at least 10 minutes forPTC to cool to ambient temperature.Measure resistance of PTC with ohmmeter.The cold resistance (RT) of any PTC device should beapproximately 100--180 percent of device ohm rating.12.5--ohm PTC = 12.5--22.5 ohm resistance (beige color)If PTC resistance is appreciably less than rating or more than 200percent higher than rating, device is defective.A94006Fig. 6 – CapacitorsCycle ProtectorCarrier thermostats have anti--cycle protection built in to protect thecompressor. Should a non--Carrier stat be utilized, it isrecommended to add a cycle protector to the system. Solid--statecycle protector protects unit compressor by preventing shortcycling. After a system shutdown, cycle protector provides for a 5± 2--minute delay before compressor restarts. On normal start--up, a5--minute delay occurs before thermostat closes. After thermostatcloses, cycle protector device provides a 3--sec delay.Cycle protector is simple to troubleshoot. Only a voltmeter capableof reading 24v is needed. Device is in control circuit, therefore,troubleshooting is safe with control power (24v) on andhigh--voltage power off.With high--voltage power off, attach voltmeter leads across T1 andT3, and set thermostat so that Y terminal is energized. Make sureall protective devices in series with Y terminal are closed.Voltmeter should read 24v across T1 and T3. With 24v stillapplied, move voltmeter leads to T2 and T3. After 5 ± 2 minutes,voltmeter should read 24v, indicating control is functioningnormally. If no time delay is encountered or device never times out,change control.Crankcase HeaterCrankcase heater is a device for keeping compressor oil warm. Bykeeping oil warm, refrigerant does not migrate to and condense incompressor shell when the compressor is off. This prevents floodedstarts which can damage compressor.On units that have a single--pole contactor, the crankcase heater iswired in parallel with contactor contacts and in series withcompressor. (See Fig. 7.) When contacts open, a circuit iscompleted from line side of contactor, through crankcase heater,through run windings of compressor, and to other side of line.When contacts are closed, there is no circuit through crankcaseheater because both leads are connected to same side of line. Thisallows heater to operate when system is not calling for cooling.The heater does not operate when system is calling for cooling.TEMP SWITCHBLK2111BLKBLKBLKCRANKCASE HTRA97586Fig. 7 – Wiring for Single--Pole ContactorThe crankcase heater is powered by high--voltage power of unit.Use extreme caution troubleshooting this device with power on.The easiest method of troubleshooting is to apply voltmeter acrosscrankcase heater leads to see if heater has power. Do not touchheater. Carefully feel area around crankcase heater. If warm,crankcase heater is probably functioning. Do not rely on thismethod as absolute evidence heater is functioning. If compressorhas been running, the area will still be warm.With power off and heater leads disconnected, check across leadswith ohmmeter. Do not look for a specific resistance reading.Check for resistance or an open circuit. Change heater if an opencircuit is detected.Time--Delay RelayThe TDR is a solid--state control, recycle delay timer which keepsindoor blower operating for 90 sec after thermostat is satisfied.This delay enables blower to remove residual cooling in coil aftercompression shutdown, thereby improving efficiency of system.The sequence of operation is that on closure of wall thermostat andat end of a fixed on delay of 1 sec, fan relay is energized. Whenthermostat is satisfied, an off delay is initiated. When fixed delay of90 ± 20 sec is completed, fan relay is de--energized and fan motorstops. If wall thermostat closes during this delay, TDR is reset andfan relay remains energized. TDR is a 24v device that operateswithin a range of 15v to 30v and draws about 0.5 amps. If theblower runs continuously instead of cycling off when the fanswitch is set to AUTO, the TDR is probably defective and must bereplaced.