Assessments - 3, GPA: 4.3
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(See Fig. 3.) High-Pressure Relief Valve (Safety Control) is located in compressor. Relief valve opens at a pressure differential of approximately 450 ± 50 psi between suction (low side) and discharge (high side) to allow pressure equalization. Internal Current and Temperature Sensitive Overload (Safety Control) resets automatically when compressor motor temperature drops to a safe level (overloads may require up to one hour to reset). 4 When an internal overload is suspected of being open, check by using an ohmmeter or continuity tester. If necessary, refer to Carrier Standard Service Techniques Manual, Chapter 2, Electrical, for complete instructions. Defrost Control, consisting of a defrost timer, defrost thermostat and defrost relay, interrupts normal system heating operation to remove frost and ice formation on outdoor coil. Frost impairs unit performance. Defrost control simultaneously stops outdoor fan, energizes reversing valve solenoid to switch system into cooling cycle (outdoor unit as condenser, indoor unit as evaporator), and activates electric heater. Unit can defrost every 90 minutes, but will do so only if outdoor temperatures are in the frosting temperature zone. For heat pump to defrost, 2 conditions are necessary: 1. Defrost timer contacts must be closed. 2. Coil temperature must be cold enough to cause defrost thermostat contacts to close. Contacts close at 28 ±3 F (50QT112 - 118) and 35 ± 3 F (50QT124, 130). Every 90 minutes of elapsed running time, the defrost timer contacts close for 10 seconds. If the defrost thermostat contacts are closed, the unit defrosts. The defrost timer limits defrosting period to 10 minutes. Normally the frost is removed and the defrost thermostat contacts will open to terminate defrosting before 10 minutes have elapsed. Defrost thermostat contacts open at 65 ±5F (50QT112 - 118) and 75 ±5F (50QT124,130). When defrosting is terminated, the outdoor fan motor is energized and reversing valve solenoid is de-energized, returning unit to heating cycle. HEAT PUMP CIRCUITS shown in Fig. 4 are refrigerant flow diagrams for heating and cooling cycles. Refrigerant Charging CÁITFÍ0&: To pfevejit pc-rsom? injury, safety gí&sses and gloves, w&eu hmdling re&igcssot ____ Do not overcharge system. An overcharge can cause compressor flooding. Unit refrigerant system is factory charged. When recharging is necessary, weigh in total charge indicated in Table 2. (Charge must be weighed in during heating season.) Remove any refrigerant remaining in system before recharging. If system has lost complete charge, triple-evacuate system to 5000 microns (29.7 in. vacuum) before recharging. Service port connections are provided on unit suction and discharge lines for evacuation and charging. (See Fig. 4 for service port location.) Dial-a-charge charging cylinder is an accurate device used to recharge systems by weight. These cylinders are available at refrigeration supply firms. Table 2 — Service Data UNIT50QT 112 115 118 124 130 MODEL 300 300 300 300 300 R-22 CHARGE* (lb) 2 7 ' 27 . ___ ___ . " 4 7 Refrig Control AccuRater™ Bypass Type INDOOR FAN Centrifugal Blower, Direct Drive, 2-Speed Rotationt CW CW CW CCW CCW Rpm 1580 1550 1570 1675 1675 Diameter (in ) 6 6 6 7 7 Width (in.) 8 430/ 550/ 575/ 885/ 1025/ Range (cfm) 375 475 480 800 960 Motor Hp % Vs % '/4 '/4 OUTDOOR FAN Propeller, Direct Drive, Single Speed Cfm 1700 1700 1700 o o o CM 2000 Rpm 1125 Diameter (in ) 15 Motor Hp Vs CCW — Counterclockwise ‘Factory refrigerant charge CW — Clockwise fLooking at fan motor shaft To check and/or adjust charge during cooling season, use Cooling Cycle Charging Charts (Fig. 5, 7, 9, II, 13) and follow Charging Chart Method below. The charging chart may also be used as an alternate method of recharging system. To check system operation during heating cycle, use Heating Cycle Operation Check Chart (Fig. 6, 8, 10, 12, 14). These charts indicate whether a correct relationship exists between system operating pressures and air temperatures entering unit. If pressure and temperature lines do not intersect on chart, the system refrigerant charge may not be correct or other system abnormalities may exist. Do not use Operating Check Charts to adjust refrigerant charge. Weigh charge into system. COOLING CYCLE CHARGING CHART METHOD 1. Operate unit a minimum of 10 minutes before checking charge, and after each charge adjustment. 2. Measure suction pressure by attaching a gage to unit suction service port. (See Fig. 4 for correct service port location.) 3. Measure outdoor (coil inlet) air dry-bulb temperature. Use service thermometer. 4. Using a sling psychrometer, measure wet-bulb temperature of air entering indoor fan coil. 5. Refer to Charging Chart. Locate on curves where outdoor air dry-bulb and indoor air wet-bulb temperature lines intersect. 6. From intersect point, project vertically downward to chart suction pressure line. ...