442 Chapter 16. Figure 16-5 Gas leak detection

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1 BRORANE BRORANEBRORANEBRORANEBRORANEBRORANEBRORANEBRORANE 442 Chapter 16 Tur n e r BRORANE FUEL EBRORANEBRORANEBRORANEBRORANEBRORANE Figure 16-5 Gas leak detection is easy. This sensitive halide detector pinpoints Freon leaks in a short time. Used on all noncombustible refrigerant (Freon) leaks, the flame changes color when the exact location of the leak is determined. (Courtesy Tumer Corporation.) 8. Open the suction valve and suction gage hose to purge the refrigerant from the system. On refrigerant Freon-12 systems where pressure is 50 psi or less, and Freon-22 systems where pressure is 90 psi or less, the expansion valve will open, allowing piping from the expansion valve to the suction service valve to purge also. If pressure is higher, it is necessary to purge the low side through the suction service valve. This can be accomplished by removing the suction-valve gage port plug and carefully opening the suction valve slightly. When the gage reads 0 pounds of pressure, close the suction service and suction-gage valves. 9. Repeat this leak check until all leaks are found and repaired. 10. When repaired, close the suction valve and disconnect the charging manifold from the unit. 11. Back-seat (open) the suction and discharge service valves. Electronic Leak Detector Although leak testing with a halide torch is considered satisfactory in most instances, a more reliable test is made by means of the electronic-type tester. This easy-to-use instrument reduces the guesswork in leak testing because it is more sensitive, faster responding, and capable of detecting a leak even though the surrounding air may be contaminated. The electronic detector contains an internal pump, which draws air and leaking halogen tracer gas (halogen gases are chlorine, bromine, fluorine, and iodine, or any of their compounds) through a probe and hose as the probe is passed over leaking joints, gaskets, welds, and so on. The air/gas mixture is drawn between two electrodes in the control unit the ion emitter and collector.

2 Maintenance 443 The leak detector contains an automatic balance circuit so that a constant or slowly changing contamination in the atmosphere will not cause the lamp to flash. Refrigerant gas will cause the lamp to flash only when there is an abrupt increase of gas going into the tip of the probe (such as when the probe tip passes near a leak). To check for a leak with the electronic detector, proceed as follows: 1. Plug the test detector into a 120-volt AC outlet. 2. Turn the sensitivity knob to the right and allow a 1-minute warm-up. 3. Check the operation by turning the sensitivity knob quickly from one position to another, which should light the probe lamp. 4. Probe for leaks, starting with maximum sensitivity. 5. If the probe lamp lights twice for each leak, reduce the sensitivity. 6. Recheck the suspected leaks for confirmation. After replacing a component in the refrigerating system, always test all joints for leaks before recharging. The extra time it takes is negligible compared to the loss of a charge caused by a faulty connection. Be sure to clean the excess soldering flux (if used) from the new joints before testing, since the flux could seal off pinhole leaks that would show up later. For new refrigerants (such as R-134a used in car air-conditioning units), use an electronic leak detector for more accurate results than with soap and water or the flame test. Evacuating the System When necessary to remove the entire refrigerant charge from the system (as in the case when an exchange of compressor or any other component of the condensing unit is necessary), proceed as follows: 1. Front-seat (close) the suction and discharge service valves. 2. Attach the charging manifold suction hose to the suction valve. 3. Connect the vacuum pump to the center port on the charging manifold. 4. Start the vacuum pump and open the suction valve. Adjust the test manifold valves so that the vacuum pump is open to the suction valve. Evacuate the system to obtain the highest vacuum possible with the vacuum pump used.

3 444 Chapter During the early stage of evacuation, it may be desired to shut off the pump at least once to see if there is a rapid loss of vacuum, indicating the presence of leaks in the system. 6. Time required for proper evacuation depends on the system and the vacuum pump. It is recommended that the vacuum pump be allowed to run for two hours or even overnight after maximum vacuum is obtained to evacuate the system. 7. Close the charging manifold valve to the vacuum pump. Stop the pump. Note the reading on the vacuum gage and allow the system to stand for 1 hour. If the vacuum has not decreased, the system is tight. 8. When the unit is checked and repaired, close the suction valve and disconnect the charging manifold from the valve. 9. To put the system in operation, back-seat (open) the suction and discharge service valves. 10. Be sure you do not allow the refrigerant to escape into the atmosphere. This is forbidden by law and strictly enforced by the Environmental Protection Agency (EPA). Checking Compressor Valves To check the compressor valves, proceed as follows: 1. Front-seat (close) the suction service valve. 2. Start the compressor and operate the unit until the compound gage shows 15 inches of vacuum. 3. Stop the compressor. 4. Back-seat (open) the suction service valve slightly to permit the vapor in the suction line to bring the gage reading back to zero. Close the valve. 5. If the pressure on the gage starts to increase, a discharge valve leak is indicated and the compressor should be replaced. 6. If the compressor will not pull at least 15 inches of vacuum on the compound gage, a suction-valve leak is indicated and the compressor should be replaced. Troubleshooting Guide In addition to the foregoing servicing details, shows the most common operating faults that can occur in residential yearround air conditioning.

4 Maintenance 445 Air-Conditioning Troubleshooting Guide Drafts. Poor air distributon. Readjust air grilles and outlets. Room temperature too low. Check thermostat setting, return-air damper, and low-pressure cutout. Shortage of air supply at grilles. Short on cooling capacity. Incorrect fan speed and incorrect pressure drop across fan. Incorrect pressure drop across evaporator coil. Excessive air turbulence at fan discharge. Improper adjustment of splitters or dampers. High duct resistance. Low fan speed. Wrong rotation of fan. Dirty filters. Check for correct change in wet-bulb temperature between entering and leaving air to cooling coil. Check refrigerating unit for capacity. Check pressure drop across the fan with draft gage, and correct fan speed. Check pressure drop across coil with draft gage. Check filters, baffles, air supply, and coil fins for obstructions. Install turning vanes in short radius elbows. Readjust dampers and check air. Check duct sizes and elbows. Inspect duct for internal obstructions. Check the drive belt for slippage. Check fan motor static control. If a multispeed fan is employed, check pulley sizes of drive. Check rotation with arrow marking on fan housing, if supplied, or by throat opening in fan housing. Change rotation by reversing motor direction. Change if throwaway type.

5 446 Chapter 16 Excessive air. Motor drive pulley too large. Check air and change pulley to correct speed. Improper damper Readjust dampers. adjustments. Lower resistance than estimated. Lower the fan speed. Air noise. Scraping noise in plenum. Squeaking and rumble. Rattles. Sharp obstruction in air stream. Small slits or openings in duct or plenum. Fan speed too high in relation to noise level and system. Obstructions in outlets. Air velocity too high at outlets. Fan hitting the fan housing. Loose belts. Dirt in bearings. Bearings sticking. Loose filter compartment. Electrical BX cable loose. Thermal-bulb tube vibrating. Housing touching pipe. Loose screws in housing. Streamline internal surfaces of the ducts. Smooth out rough edges. Close all holes or openings. Decrease fan speed, if possible, or install sound-absorption material in ducts. (Sound insulation should be fireproof material.) Remove obstruction, if possible, without throwing system out of balance. If removal is not possible, try changing location of angle. Rebalance air in system. Adjust fan to turn free on all sides. Tighten belts. Clean the bearings. Remove and replace. Examine shaft. Tighten. Fasten securely. Clear vibrating point of tube. Insulate metal-to-metal location. Tighten.

6 Maintenance 447 Water leaking or dripping from unit. Vibration. Hissing noise at expansion valve. Improper drain piping. Dirt in condensate pan and screen. Loose pipe fittings and valves. Condensate overshooting drain pan. Loose motor mounting. Improper weight distribution on hangers or feet. Belt too tight, causing whip in shaft. Pulleys loose or out of line. Fan shaft sprung. Shaft bearings worn. Fans out of balance or loose on shaft. No canvas breaker strips to duct connection. Shortage of refrigerant. Clogged strainer. Pressure drop in liquid. Drain should pitch 1 / 4 to 1 in/ft. Drain should be properly trapped. Condensate pan must pitch water toward the drain. Remove screen, clean pan, and flush with water. Tighten all connections and packing glands of valves. Air velocity too high through coils. Check resistance pressure and fan speed to determine if they are in accordance with design conditions. Tighten motor mounting bolts. Level unit on all sides. Adjust belt tension. Align pulleys and tighten pulley set screws. Remove and replace with new shaft. Replace with new bearings. Tighten if shaft is not worn from loose play. Replace if badly damaged. Install breaker strips. Add refrigerant to proper liquid level. Remove and clean screen. Check head pressure.

7 448 Chapter 16 Heating of liquid Subcooling necessary. line from outside surroundings. No liquid at top expansion valve in bank of coils. Install gas head on liquid line about 2 feet higher than top valve. Partial frosting and sweating of coil. Failure to cool and no frost. Failure to cool and complete frosting. Too cool. Shortage of refrigerant. Restricted or clogged liquid line. Too much outside air being taken on one side of coil. Expansion valve too small or improperly adjusted. Solenoid valve sticking. Solenoid valve clogged. Solenoid coil burned out. Condensing unit shut off. Liquid line valve closed. Thermostat faulty. Fan not running. Insufficient air. Air outlets closed. Coil clogged with dirt. Improper setting of room thermostat, or thermostat faulty. Wrong outlet distribution. Add refrigerant. Pump down system and clean out. Change mixing chamber for better distribution. Check valve capacity and superheat adjustment. Remove and clean. Remove and clean. Replace coil. Start compressor. Open valve. Repair or replace. Start fan. Dirty filters. Dampers stuck shut. Correct air distribution. Remove coil and clean thoroughly. Correct thermostat. Balance air distribution correctly.

8 Maintenance 449 Frequent Clogged liquid line. Clean out. cycling of unit. Insufficient Add refrigerant. refrigerant. Improper setting of Adjust valves properly. expansion valves. Fan stopped Check fan circuit and start fan. running. Thermostat Reset differential. differential setting too close. Thermostat in direct Relocate thermostat. line of air-throw from grille. Evaporator coil frosted. Run fan with compressor shut off to defrost coil. Motor overheats. Motor fails to run. Failure of system to heat properly. Lack of oil or improper oil. Wrong voltage. Overload. Belts too tight. Ambient room temperature high. Improper fuse. Thermal overload too small. Improper wiring. Heating coils not properly trapped. Air trapped in coils. Heating coils improper distance above boiler. Oil bearings with recommended oil. Check with electrician and power company. Reduce fan speed, if possible, without impairing air quantity. Replace with larger motor if necessary. Adjust belt tension. Check motor rating with manufacturer of motor. Check fuses for proper sizing. Check with motor data sheet. Check with wiring diagram. Separate trap should be provided for each coil. Coils should be properly vented. Distance above boiler line should be at least 18 inches.

9 450 Chapter 16 Supply or return lines too small. Install proper size piping for coils. Resistance too great Install proper size piping. in system. Too much outside air being introduced. Use as much recirculated air as possible without impairing the calculated ratio of outside recirculated air. Heating coils not leveled. Level coils to obtain proper coil drainage. Condensate in coils. Traps may contain scale and sediment preventing operation. Failure of system to humidify. Water supply failure. Too much outside air. Control valve on humidifier supply closed or clogged. Capacity of humidifier insufficient. Humidistat not functioning. Air passing directly over and through humidistat. Water valve closed. Strainer plugged. Nozzle clogged. Close down on outside damper. Remove and clean. Install larger or additional humidifier and supply line. Inspect humidistat for adjustment and dirt, especially the hair suspension. Place baffle on upstream side of humidistat to break air around instrument. Summary A malfunctioning system may be caused by one portion of the system or a combination of several portions. It is necessary and advisable to check the more obvious causes first. Each part of the system has a certain function to perform, and, if any individual part does not function properly and efficiently, the performance of the entire airconditioning system will be affected. To simplify servicing a system, the service technician should remember that the refrigerant, under proper operating conditions,

10 Maintenance 451 travels through the system in one specific direction. The service technician can trace the path of refrigerant through any system, beginning at the compressor. Pressure, temperature, volume, and heat-absorbing characteristics of the refrigerant in the various parts of the system are essential in analyzing air-conditioning problems. When a refrigerant piping system is completed, the system should be checked very carefully for leaks. The most effective way of finding a leak in a Freon system is with a halide-leak detector. Testing with soap and water or with oil at the joints will locate only the larger leaks. To test for noncondensables, run the condenser fan for 10 minutes with the compressor off. Measure the head pressure. Add 10 For 5.6 C to the ambient air temperature. Convert this temperature to pressure. It should equal the head pressure. If the head pressure is greater than this, there is a probability of a noncondensable gas in the system. Review Questions 1. What is the general practice in the diagnosis of a malfunctioning air-conditioning system? 2. When do you use a systematic procedure in checking to determine the source of trouble in an inoperative system? 3. Describe head-pressure checking methods. 4. What may the reason be for a low suction pressure? 5. What are the usual causes of low back pressure? 6. What is the method used in checking refrigerant charge? 7. Describe the types of compressor gages and give pressure ranges. 8. What is the advantage in using a combination gage set? 9. Describe the method of adding and removing refrigerant. 10. What is meant by system pump-down and how is it accomplished? 11. Why is it necessary to leak-test a refrigeration system prior to operation? 12. Describe the method of evacuating a refrigeration system. 13. What is the procedure used in checking compression valves? 14. What does backseat mean? 15. List three noncondensables.