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 22 page image

22Electrical FailuresThe compressor mechanical pump is driven by an electric motorwithin its hermetic shell. In electrical failures, compressor does notrun although external electrical and mechanical systems appearnormal. Compressor must be checked electrically for abnormalities.Before troubleshooting compressor motor, review this descriptionof compressor motor terminal identification.Single--Phase MotorsTo identify terminals C, S, and R:1. Turn off all unit power.2. Discharge run and start capacitors to prevent shock.3. Remove all wires from motor terminals.4. Read resistance between all pairs of terminals using anohmmeter on 0--10 ohm scale.5. Determine 2 terminals that provide greatest resistancereading.Through elimination, remaining terminal must be common (C).Greatest resistance between common (C) and another terminalindicates the start winding because it has more turns. This terminalis the start (S). The remaining terminal will be run winding (R).NOTE: If compressor is hot, allow time to cool and internal linebreak to reset. There is an internal line break protector which mustbe closed.All compressors are equipped with internal motor protection. Ifmotor becomes hot for any reason, protector opens. Compressorshould always be allowed to cool and protector to close beforetroubleshooting. Always turn off all power to unit and disconnectleads at compressor terminals before taking readings.Most common motor failures are due to either an open, grounded,or short circuit. When a compressor fails to start or run, 3 tests canhelp determine the problem. First, all possible external causesshould be eliminated, such as overloads, improper voltage,pressure equalization, defective capacitor(s), relays, wiring, etc.Compressor has internal line break overload, so be certain it isclosed.Open CircuitUNIT PERSONAL INJURY HAZARDFailure to follow this warning could result in personal injury.Use caution when working near compressor terminals.Damaged terminals have the potential to cause personal injury.Never put face or body directly in line with terminals.! WARNINGTo determine if any winding has a break in the internal wires andcurrent is unable to pass through, follow these steps:1. Be sure all power is off.2. Discharge all capacitors.3. Remove wires from terminals C, S, and R.4. Check resistance from C--R, C--S, and R--S using anohmmeter on 0--1000 ohm scale.Because winding resistances are usually less than 10 ohms, eachreading appears to be approximately 0 ohm. If resistance remains at1000 ohms, an open or break exists and compressor should bereplaced.UNIT DAMAGE HAZARDFailure to follow this caution may result in equipmentdamage or improper operation.Be sure internal line break overload is not temporarily open.CAUTION!Ground CircuitTo determine if a wire has broken or come in direct contact withshell, causing a direct short to ground, follow these steps:1. Allow crankcase heaters to remain on for several hoursbefore checking motor to ensure windings are not saturatedwith refrigerant.2. Using an ohmmeter on R X 10,000 ohm scale ormegohmmeter (follow manufacturer’s instructions).3. Be sure all power is off.4. Discharge all capacitors.5. Remove wires from terminals C, S, and R.6. Place one meter probe on ground or on compressor shell.Make a good metal--to--metal contact. Place other probe onterminals C, S, and R in sequence.7. Note meter scale.8. If reading of 0 or low resistance is obtained, motor isgrounded. Replace compressor.Compressor resistance to ground should not be less than 1000ohms per volt of operating voltage.Example:230 volts X 1000 ohms/volt = 230,000 ohms minimum.Short CircuitTo determine if any wires within windings have broken throughtheir insulation and made contact with other wires, thereby shortingall or part of the winding(s), be sure the following conditions aremet.1. Correct motor winding resistances must be known beforetesting, either from previous readings or frommanufacturer’s specifications.2. Temperature of windings must be as specified, usuallyabout 70_F.3. Resistance measuring instrument must have an accuracywithin ± 5--10 percent. This requires an accurate ohmmetersuch as a Wheatstone bridge or null balance--typeinstrument.4. Motor must be dry or free from direct contact with liquidrefrigerant.Make This Critical Test(Not advisable unless above conditions are met)1. Be sure all power is off.2. Discharge all capacitors.3. Remove wires from terminals C, S, and R.4. Place instrument probes together and determine probe andlead wire resistance.5. Check resistance readings from C--R, C--S, and R--S.6. Subtract instrument probe and lead resistance from eachreading.If any reading is within ±20 percent of known resistance, motor isprobably normal. Usually a considerable difference in reading isnoted if a turn--to--turn short is present.