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Keeping your cool
Page 98
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by Jerry Rodwell
REFRIGERATION units on commercials have a hard life, with hours of continuous running, to protect valuable temperature sensitive loads.
Yet operators tend to take these complex units for granted until something goes wrong and a load is ruined.
Despite their complexity, there are many maintenance operations that a good mechanic can carry out on fridge units, so saving money otherwise spent in having an outside specialist do the job.
Fridge experts Marshalls of Cambridge explained some of the general maintenance operations that any operator can do in his own works, so saving money.
These operations are based on a Thermo King NWD 50, but the same tips apply to many other fridge units.
Every day the oil level should be checked, and if necessary topped up with ordinary engine oil. Check the radiator water level at the same time, and don't forget to add anti-freeze in 50/50 ratio. After each 250 hours of running, the engine oil and filter should be changed. Current models have a filter that needs to be drained by opening a tap below it before replacing the element, but new models will have a spin-off filter that can be thrown away and replaced complete.
Tighten all mounting bolts, and clean and defrost the drains. The air filter assembly should be checked and serviced if needed, and all control linkages lubricated. Make sure that the fan bearings, both front and back, are lubricated weekly with six pumps of the grease gun through the nipples located inside the nearside cover.
Some drive belts in the Thermo King are very long, expecially the one driving the fan. All need careful checking and replacing if at all worn. A set of belts costs around £20 not much compared against the value of a lost cargo.
The water pump belt should have 1.27 cm (1/4 in) free play at mid-point of its longest run, and the fan drive belt 2.54-3.81cm (1-11/4 in) at the same point.
Pump drive belt adjustment is by unbolting the two pieces of the pump pulley and removing or adding shims between, and the fan drive belt by loosening the jockey wheel mounting plate bolts, then altering the single adjusting bolt to achieve correct tension. Don't forget to relock this bolt, and tighten the plate mounting bolts.
Battery water and terminals should be checked, and the charging rate checked at 5 10 amps normal running.
While the unit is running, check that oil pressure is 655-690kN/ sq m (95-100 psi) and certainly not less than 550kN/ sq m (80 psi). Water temperature should run at 77-82°C (170-180°F). Electric motor mountings an bearings need checking for free pla: and the electric standby system neec checking out.
Clean condenser coil, and mak sure the damper door on the machin outlet closes securely on the defro! cycle.
There is a sight glass under the oft side inspection cover for th refrigerant level, but topping-up is specialist job, so don't attempt yourself.
Safe working pressure in th refrigerant system is 1,792kN / sq r (260 psi), and a safety switch on th manifold cuts the machine off about 2,896k N / sq m (420 psi) i exceeded. Drivers often use a gel you-home dodge of shorting the tw leads to this switch together on such failure in order to restart the fridgc but this can lead to extensive an expensive damage.
It is worth remembering that o these Thermo King units, when th box temperature is set at minus 9°( (minus 16° F) or lower, it wi continually freeze down to its lowe working temperature. This is becaus goods carried at minus 9°C migh just as well be deep frozen.
Normally the unit will alternat between a heating and coolin operation to keep the outlet are defrosted.
And on those units that switch of completely when the set temperatur has been reached, it should b remembered that if the load is beim the set temperature when put into th box, then the unit will not start ur To check operation before setting ou on a haul, turn the thermostat t. below normal temperature to mak sure the fridge will start. Then reset t. correct temperature.
When working on fridges, th electric standby/ diesel runnin switch should be put in the electri position -without the extern@ electric supply connected. This wil ensure that no one can inadvertentl start the diesel engine up while some one's hand is in the works.
This list of general maintenanc points covers things that need cloin; after 250 hours running. At the 500 hour point the unit should go to ; Specialist since refrigerant charge am thermostat calibrations need check ing with special equipment.
But any operator who does his owl basic maintenance as outlined heni will at least ensure that his fridge — worth up to £3,650 — keeps goinl reliably on the road. And well main tamed units have a life of 15 years o more — while some are wrecked bi poor maintenance within months.