Carrier 48MPD Installation, Start-up And Service Instructions Manual

Contents

Replace the filter cores whenever the moisture/liquid in-dicator shows moisture in the system.Follow instructions on the packaging for the replacementcores for disassembling and reassembling the filter assem-blies and housings.Liquid Line Service Valve — Located immediatelyahead of the filter drier, this valve has a 1⁄ 4-in. flare connec-tion for field charging. With the liquid circuit shut, the com-pressor can be used to pump the refrigerant down into thehigh side. The refrigerant can then be stored there by closingthe compressor discharge valve.Compressor Suction and Discharge ServiceValves — Each compressor is provided with suction anddischarge service valves. With these valves, the compressorcan be isolated from the refrigerant system for servicing orreplacing.High-Pressure Switch — This switch has nonadjust-able settings. Figure 60 shows connection on a cylinder head.See Table 31 for pressure switch settings.Table 31 — Pressure Switch Settings,Psig (kPag)SWITCH CUTOUT CUT-INHigh 426 ± 7 320 ± 20(2935 ± 48) (2205 ± 138)Low 27 ± 4 67 ± 7(186 ± 28) (462 ± 48)NOTE: High-pressure switch must be removed from cylin-der head before removing compressor from the unit.TO CHECK — Slowly close the discharge shutoff valveuntil the compressor shuts down. This should be at approx-imately 426 psig (2935 kPag). Slowly open the valve. Whenthe pressure drops to approximately 320 psig (2205 kPag),the pressure switch resets. To reenergize the control circuit,manually switch the fan circuit breaker off and then on. Thecompressor starts again under Time Guardt controls.Low-Pressure Switch — The low-pressure switch (LPS)has fixed nonadjustable settings. It is located at the pumpend of the compressor above the bearing head. See Table 31for pressure switch settings.TO CHECK — Slowly close the suction cut-off valve andallow the compressor to shut down. This should occur atapproximately 27 psig (186 kPag). Slowly open the valve.The compressor restarts under Time Guard control when thepressure builds to approximately 67 psig (462 kPag).Pressure Relief — High-side pressure relief isprovided by a fusible plug in the liquid line at the serv-ice valve. For low-side pressure relief, a fusible plug isinserted in the side of the accumulator. See Fig. 60. A pres-sure relief valve installed on the compressor relieves at450 psig (3102 kPag).AdjustmentsEVAPORATOR FAN AND POWER EXHAUST MOTORPLATE — Adjust using a 15 ⁄16-in. wrench on the adjustingbolts:1. Loosen holddown bolts. (See Fig. 61.)2. Turn the adjusting bolts to move the motor mounting platetoward or away from the fan to loosen or tighten the belts.Make the same number of turns to each bolt.3. Retighten holddown bolts.BELT INSTALLATION AND TENSIONINGIMPORTANT: When installing or replacing belts, al-ways use a complete set of new, matched belts to pre-vent potential vibration problems. Mixing belts oftenresults in premature breakage of the new belts.1. Turn off unit power.2. Adjust motor plate so belts can be installed without stretch-ing over the grooves of the pulley. (Forcing the belts canresult in uneven belt stretching and a mismatched set ofbelts.)3. Before tensioning the belts, equalize belt slack so that itis on the same side of the belt for all belts. Failure to doso may result in uneven belt stretching.4. Tighten belts using the motor plate adjusting bolts.5. Adjust until proper belt tension (1/2-in. deflection withone finger) is obtained. Be sure to adjust both adjustingbolts the same number of turns.NOTE: Check the tension at least twice during the firstday of operation, as there is normally a rapid decrease intension until the belts have run in. Check tensionperiodically thereafter and keep it at the recommendedtension.With the correct belt tension, belts may slip and squealmomentarily on start-up. This slippage is normal and dis-appears after wheel reaches operating speed. Excessive belttension shortens belt life and may cause bearing and shaftdamage.50