Carrier 38E - User Manual

Function Description: The Time Guard II is a solid-state device designed to protect the unit compressor by preventing short cycling. After a system shutdown, it introduces a 5 ± 2-minute delay before the compressor restarts. During normal start-up, a 5-minute delay occurs before the thermostat closes. Once the thermostat closes, the Time Guard II provides a 3-second delay to prevent contactor chattering.

Usage Features: The Time Guard II device is simple to troubleshoot, requiring only a voltmeter capable of reading 24V. Since it operates within the control circuit, troubleshooting can be performed safely with control power (24V) on and high-voltage power off. To check its operation, with high-voltage power off, attach voltmeter leads across T1 and T3. Set the thermostat to energize the Y terminal, ensuring all protective devices in series with the Y terminal are closed. The voltmeter should read 24V across T1 and T3. With 24V still applied, move the voltmeter lead from the T1 terminal to the T2 terminal. After 5 ± 2 minutes, the voltmeter should read 24V, indicating normal control function. If no time delay is observed or the device never times out, the control should be changed. A schematic diagram printed on the device itself can assist in troubleshooting.

Crankcase Heater

Function Description: The crankcase heater is a device designed to keep the compressor oil warm. By maintaining warm oil, it prevents refrigerant from migrating to and condensing within the compressor shell. This, in turn, prevents flooded starts which can cause severe damage to the compressor.

Usage Features: Crankcase heaters come in two basic types: wraparound (belly-band) type, which is wrapped externally around the compressor shell, and insertion type, which is inserted into the compressor oil well. Both types are found in this family of units. The crankcase heater is powered by the unit's high-voltage supply.

Maintenance Features: Extreme caution must be exercised when troubleshooting this device with power on. The easiest troubleshooting method is to apply a voltmeter across the crankcase heater leads to check for voltage. Carefully feeling the area around the crankcase heater can indicate if it is warm, suggesting it is likely functioning. However, this method should not be solely relied upon as absolute evidence, as the area may still be warm if the compressor has recently been running. With power off and heater leads disconnected, check for continuity across the leads with an ohmmeter. Do not look for a specific resistance reading, but check for resistance or an open circuit. If an open circuit is detected, the heater should be changed. Some crankcase heaters in this series are equipped with a crankcase heater switch in series with the heater. This energy-saving device shuts off power to the heater when temperatures are high enough that the heater is not needed. Ensure this switch is functioning normally before condemning the crankcase heater.

Pressure Switches

Function Description: Pressure switches are protective devices wired into the control circuit (low voltage). They shut off the compressor if abnormally high or low pressures are present in the refrigeration circuit. Depending on the unit model, a low- or high-pressure switch, or both, may be present in the system.

Low-Pressure Switch: Located on the suction line, this switch protects against low suction pressures caused by issues such as loss of charge, low airflow across the indoor coil, or dirty filters. It opens on a pressure drop at approximately 30 psi. If the system pressure is above this, the switch should be closed.

High-Pressure Switch: Located on the discharge line, this switch protects against high discharge pressures caused by events such as overcharge, condenser fan motor failure, or system restriction. It opens on a pressure rise at about 425 psi. If system pressures exceed this setting during abnormal conditions, the switch opens. Do not attempt to simulate these system abnormalities, as high pressures pose a serious safety hazard.

Liquid Line Pressure Switch: Found on the liquid line, this switch is used exclusively in heat pump systems. Its function is similar to a conventional low-pressure switch. However, because heat pumps experience very low suction pressures during normal system operation, a conventional low-pressure switch cannot be installed on the suction line. Instead, this switch is installed in the liquid line and acts as a loss-of-charge protector, opening at 5 psi.

Usage Features: To check any pressure switch, turn off all power to the unit, disconnect the leads from the switch, and apply ohmmeter leads across the switch. A good switch should show continuity. Because these switches are attached to a refrigeration system under pressure, it is not advisable to remove them for troubleshooting unless a problem is reasonably certain. If a switch must be removed, bleed all system charge until the pressure gauge reads 0 psi. When brazing, wear safety glasses and gloves, apply heat with a torch to the solder joint, and have a quenching cloth available. Oil vapor in the line may ignite if the switch is removed. Braze in a 1/4-inch flare fitting and screw on the replacement pressure switch, observing all safety precautions.

Defrost Thermostats

Function Description: The defrost thermostat signals the heat pump when conditions are appropriate for defrost or when conditions have changed to terminate defrost. It is a thermally actuated switch clamped to the liquid line to sense its temperature. The normal temperature range for closing is 27 ± 5°F and for opening is 80 ± 5°F.

Usage Features: Since the defrost thermostat is central to the defrost system, its troubleshooting procedure is detailed below.

Printed-Circuit Control Board

Function Description: The solid-state defrost control board used on 38QH, QN, QS heat pumps replaces the electro-mechanical timer and defrost relay found on previous Carrier Chronotemp™ defrost systems. This defrost control board can be set to check the need for defrost every 30, 50, or 90 minutes of operating time. It also includes an additional feature that allows the unit to restart in a defrost cycle if the room thermostat is satisfied during defrost.

Usage Features: Troubleshooting the defrost control involves a series of simple steps to identify if the board is defective. First, ensure the unit operates properly in heating and cooling modes to rule out problems not attributed to the defrost control board. Then, turn the thermostat to OFF and disconnect all power to the outdoor unit. Remove the control box cover to access electrical components and the defrost control board. Disconnect the defrost thermostat leads from the control board and connect them to an ohmmeter. The thermostat leads are heavy-gauge black insulated wires connected to the DFT and C terminals on the control board. A resistance reading of 0 indicates a closed defrost thermostat, while infinity (∞) indicates an open thermostat, depending on the outdoor temperature. Jumper between the DFT and C terminals on the control board as shown in Fig. 9. Disconnect the outdoor fan motor lead and tape it to prevent grounding. Restart the unit in heating, allowing frost to accumulate on the outdoor coil. After a few minutes in heating, the liquid line temperature should drop below the closing set point of the defrost thermostat. Use an ohmmeter to check the resistance across the defrost thermostat leads. A resistance of 0 indicates the defrost thermostat is closed and operating properly. Remove the protective cover from the TPI and TP2 speed-up terminals. Insert a jumper wire into the protective cover, then reinsert the cover on the speed-up terminals. This reduces the timing sequence to 1/4 of the original time (see Fig. 10). For a 30-minute timing cycle, the unit initiates defrost within approximately 30 seconds; for a 50-minute setting, within 50 seconds; and for a 90-minute setting, within 90 seconds. When the reversing valve changes position, remove the protective cover/jumper; otherwise, the control will terminate the normal 10-minute defrost cycle in approximately 10 seconds. Do not use a screwdriver or other means to short the speed-up pins, as accidentally grounding the pins will destroy the control board. With the unit operating in defrost mode, use a voltmeter to check between R and W2 as shown in Fig. 11. The voltmeter reading should indicate zero volts, ensuring that the defrost relay contacts have closed, energizing supplemental heat and the reversing valve solenoid. The unit should remain in defrost for no longer than 10 minutes. The actual defrost time depends on how quickly the speed-up jumper is removed. If it takes 3 seconds to remove the speed-up jumper after the unit has switched to defrost, only 7 minutes of the defrost cycle remain. After a few minutes in defrost (cooling) operation, the liquid line should be warm enough to have caused the defrost thermostat contacts to open. Check the resistance across the defrost thermostat; the ohmmeter should read infinite resistance, indicating the defrost thermostat has opened. Shut off unit power and reconnect the fan lead. Remove the jumper wire from the speed-up terminal protective cover and reinsert the cover. Failure to remove the jumper causes the unit to speed up operating cycles continuously. Remove the jumper between the DFT and C terminals and reconnect the defrost thermostat leads. Replace the control box cover and restore power to the unit.

Maintenance Features: If the defrost thermostat does not check out following the above steps or if incorrect calibration is suspected, check for a defective thermostat as follows: Follow steps 1-5 above. Using a thermocouple temperature measuring device, route the sensor or probe underneath the coil (or other convenient location) and attach it to the liquid line near the defrost thermostat. Insulate it for a more accurate reading. Restart the unit in heating. Within a few minutes, the liquid line temperature drops within a range that causes the defrost thermostat contacts to close. The temperature range is from 32°F to 22°F. Note the temperature at which the ohmmeter reading goes from ∞ to 0 ohms, as this is when the thermostat contacts close. Remove the protective cover from the TPI and TP2 speed-up terminals, insert the jumper wire into the protective cover, and reinsert the protective cover on the speed-up terminals. The unit changes over to defrost within 90 seconds (depending on the timing cycle setting). The liquid line temperature rises to a range where the defrost thermostat contacts open. The temperature range is from 75°F to 85°F. The resistance goes from 0 to ∞ when the contacts open. If either the opening or closing temperature does not fall within the above ranges, or if the thermostat sticks in one position, replace the thermostat to ensure proper defrost operation.

Fan Motors (See Fig. 12.)

Function Description: The fan motor powers the fan that draws air through the outdoor coil to perform heat exchange. The motors are totally enclosed to increase reliability and eliminate the need for a rain shield. They are provided with a color-coded terminal block to facilitate removal. Oilers are provided on the motor bearings.

Maintenance Features: Oiling holes are provided at each end of the condenser fan motor. Remove the fan motor and lubricate it with 32 drops (16 drops per hole) of SAE 10 non-detergent oil at the following intervals: a. Annually, when the environment is very dirty, the ambient temperature is higher than 105°F (40°C), and the average unit operating time exceeds 15 hours a day. b. Every 3 years, when the environment is reasonably clean, the ambient temperature is less than 105°F (40°C), and the unit operating time averages 8 to 15 hours a day. c. Every 5 years, when the environment is clean, the ambient temperature is less than 105°F (40°C), and the unit operating time averages less than 8 hours a day. After lubrication, ensure the fan prop is positioned correctly on the motor shaft (See Fig. 13). Fan motors should generally not present troubleshooting problems. A motor with seized or tight bearings can sometimes be saved or have its life extended by adding oil to the bearings. For suspected electrical failures, check for loose or faulty electrical connections or a defective fan motor. The fan motor is equipped with a thermal overload device in its windings, which may open under adverse operating conditions. Allow time for the motor to cool so the device can reset. Further checking of the motor can be done with an ohmmeter. Set the scale to R x 1 position and check for continuity between the 3 leads. Replace motors that show an open circuit in any of the windings. Place one lead of the ohmmeter on each motor lead and the other on the motor case (ground). Replace any motor that shows resistance to ground. Any motor showing signs of arcing, burning, or overheating should be considered suspect and replaced.

Service Sentry Control Board

Function Description: The Service Sentry control provides immediate warning when the outdoor heat pump requires servicing. It turns on the indoor thermostat light if the compressor does not operate for either heating or cooling. This feature enables the owner to obtain speedy heat pump service during the heating season, reducing supplementary electric heat costs, and during the cooling season, reducing the period of heat discomfort (Fig. 14).

Usage Features: The Service Sentry is an accessory device. On heat pump DL and CD option packages, a slightly different version of the Service Sentry is installed as standard equipment. It functions almost identically to the accessory Service Sentry, except that it locks out the compressor under certain adverse operating conditions. The system is manually reset by shutting it off at the thermostat subbase, then turning it back on. If the adverse condition is corrected, the system restarts. An example of an adverse condition could be if the system is located in a desert climate where high operating temperatures may cause the system to shut down on the high-pressure switch or the compressor internal overload.

The Service Sentry requires two inputs:

It must sense a 24V input from the thermostat. As the thermostat calls for heating or cooling, it supplies 24V to the Service Sentry device.
A current transformer (or induction loop), similar to a clamp-on ammeter, senses the current draw in the compressor lead. The induction loop must sense a minimum current draw when the thermostat is calling for heating or cooling. Notes:
On a single-phase compressor, the induction loop senses current in the common leg.
On a 3-phase compressor, the induction loop senses current in one of the phases.

Troubleshooting the Service Sentry device is easy. With the thermostat calling for heating or cooling and the compressor running, the indoor thermostat light should be off. If it is on, check for wiring errors or replace the Service Sentry. To check for correct operation, shut off the circuit breaker or disconnect switch to the outdoor unit while it is running. The signal light on the thermostat should light. If this does not occur, check for wiring errors or replace the Service Sentry.

Maintenance Features: If the Service Sentry needs replacing, shut off all power to the unit before attempting repairs. Use the Service Sentry control with single-phase Carrier heat pumps equipped with a 24V control circuit. Connect the black, orange, and red pigtails (24V) on the Service Sentry to the outdoor unit control circuit terminal board (See Fig. 15 and the wiring diagram on the unit). An extra control wire is required between the L terminals on the outdoor unit, indoor unit, and thermostat subbase (the L terminal is currently being added to outdoor and indoor unit terminal blocks). If the units do not already have an L terminal, splice a control wire between the L terminals on the Service Sentry and the thermostat subbase. Terminal L is labeled terminal X on some thermostat subbases (all future subbases will read terminal L). Connect all field line power wires to the unit in the usual manner. However, route one field line power supply wire through the metallic loop on the bottom of the Service Sentry, then to the normal unit connection. On 015 (230-1-60) and 018 (230-1-60) units, pass the supply wire through the metallic loop twice, as shown in Fig. 14 and 15. On all other units, pass the supply wire through the loop only once.

Outdoor Thermostats (See Fig. 16.)

Function Description: The outdoor thermostat brings on stages of electric heat as the outdoor temperature and heat pump output drop. The setting at which the thermostat closes is variable, depending on the design of the system. It is set at the time of installation and should not be changed without good reason. Up to 2 outdoor thermostats may be installed. Some systems may not have any thermostat.

Usage Features: Although these devices are installed in the control circuit (24V), turn off all power to the unit before attempting to troubleshoot the thermostat. Use a standard ohmmeter to check for continuity through the thermostat. If you suspect the thermostat is out of calibration, use a calibrated electronic thermometer to determine the correct outdoor temperature. Insert a screwdriver blade in the adjustment slot and turn the thermostat switch until it closes. Observe this using an ohmmeter across the switch. Read the temperature setting when the switch closes. It should be close to the reading observed using the electronic thermometer. Any setting within ± 5 degrees is acceptable.