I Visually check the unit, both static and running. As a
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safety mea sure, turn the run/stop switch on the machine to stop. Check all drive belts for correct tension. Drain the engine oil, either through the short drain hose with an extension tube or using an extractor pump to suck old oil through the dipstick hole. Smear fresh oil on the new filter's flange seal before replacing the old one; add 8.0 litres of new 15/40 grade engine oil. Cover the area beneath the oil bath air filter, then dismantle it for cleaning and add fresh engine oil. Replace the in-line and the primary fuel filters. AM Check the
compressor oil level then run the unit on 'cool' for up to 15 minutes; change to 'heat' and run it for another 15 minutes. Then recheck the oil and top up if necessary. Fit a set of manifold gauges to the service valves and test its capacity, With R22, expect readings of around 170psi (11.5 bar) of head pressure and 20psi (1.4 bar) of suction pressure. The figures can be verified via the in-built transducer or from the in-cab display.
Al% Using the sight glass, check the refrigerant gas levels for charge and contamination. When dry it remains green but it turns yellow when there's moisture. In this case the system will need reclaiming before re-charging. To protect the ozone layer, all old gas must be returned to an official supplier for recycling (ThermoTrans uses Casco). To remove any moisture, charge the system via the manifold gauges with oxygen-free nitrogen; evacuate for 24 hours and re-charge with fresh gas. The Supra 722 holds 5.2kg of HCFC22. Leaks can be detected using an electronic detector—or soapsuds. 4Check that all cables, conduits and connections are corrosion-free and clear of any moving parts, and that no chafing can occur. Ensure that the battery is dry, clean and secure, and that the terminals are both tight and corrosionfree. Ensure that the battery voltage is correct. Examine the alternator brushes and replace if worn. Check the calibration of the box's outer temperature gauge via the in-cab display.
5Test the air switch operation to ensure that the system will defrost when required. Check the timer setting and the correct operation of the three-way valve, that the fans stop and defrost ceases. One way to test the air switch, is to connect a magnehelic gauge to the outlets behind the evaporator. It reads in inches of water and must be calibrated first. With the Supra 722 the air switch should open at 0.75in to set the unit on defrost; this simulates a rise in back pressure from the evaporator caused by a build-up of ice.
6From inside the body, check on the amount of bearing wear by rocking the tips of the blades. Examine the brushes of the fan motors; there are two per motor and these usually last around 2,000 hours from new. They cost a few pounds apiece but if they're forgotten it can prove very expensive in downtime and lost custom. Ensure that water drains from the evaporator too.