dishwasher DISHWASHING MACHINE MAINTENANCE & REPAIR (Throop Church) by David S. Lawyer, May 1992 Contents: INSTRUCTION & PARTS MANUAL HOW IT WORKS MAINTENANCE & REPAIR For information on how to operate this Sterno Dishwasher at Throop see the files: dw_oper_long and/or dw_oper_short. It's a good idea to read these and inspect the physical machine before reading this document. Our model number is SDRA-Single Phase made in the 1960's. Today (1992), commercial dishwashers like ours sell for several thousand dollars. INSTRUCTION & PARTS MANUAL: Stero has an "Instruction & Parts Manual" which covers all "Stero Door Machines" but it is sometime hard to use because: 1. It has no index, contents table, page numbers, or circuit diagrams. 2. Many of the parts shown are not used in our machine. 3. It contains no step-by-step operating instructions. Ignore all pages in the "Instruction & Parts Manual" concerning steam heat, heat exchangers, gas heat, automatic fill control, door safety switch, magnetic door lock, and manual fill valves, since Throop's machine doesn't have them. There is no information on the detergent dispenser or about the rinse solution dispenser because they are made by another company: EL = Economics Laboratory. HOW IT WORKS: See the file "dishw-how-it-works" for a clearer explanation but with less technical details. We have a separate circuit diagram (which I ordered) but no explanation. With some effort, one may figure out how it works if one is familiar with relay logic, etc. The fill relay coil C is missing from the circuit diagram. It likely replaces the wire shown going downward from terminal 8 of the fill relay. On the diagram the "MTR. CON. COIL" is Contactor A and "CR" is the coil of Control Relay B. "E-TOP" is a cam operated contact on the Clock (Timer) E. So is "E-BOTTOM". Note that we have no Electric Booster (15 kw heater for the rinse water). We do have a 5kw tank heater which may keep the wash water hot enough (150 deg.) to kill bacteria. Since the rinse water is fresh (not reused like it is when you wash dishes in dishpans), the lower temperature rinse (due to the absence of a booster heater) should not contaminate the dishes. However the cooler rinse will cause the dishes to dry a little slower. The "two-way diaphragm valve" is actually a solenoid valve for turning on and off the incoming water supply. (Our garbage disposal uses a similar valve but it's made by JE = Jackes Evans.) The main part of the valve uses water pressure for its operation instead of electric energy. The electric solenoid only operates a "pilot" valve which controls the flow of water to the pressure chamber used for operation of the main valve. A full page diagram of the solenoid may be found many pages beyond the instruction sheet page. To understand the flow of water in the machine see the diagram labeled "door machine plumbing". The building hot water pipe feeds the line strainer (see a full page diagram later on) which infrequently (every 10 years ?) needs cleaning. The water then goes thru the solenoid valve to the vacuum breaker. This breaker (located high up on the left rear of the machine) has been known to stick but taping it may fix it. If the sprayers fail to spray when the machine is first turned on (switch turned to "auto") then a stuck vacuum breaker may be the cause. The main pump (not shown) supplies wash water to the bottom tee (18) from where it then flows to the upper and lower wash arms. The heating element is supposed to be submerged in the washwater but it will go on even if no water is in the tank. It should have been interlocked with the fill relay so that heat could not be turned on until the tank is fill. However, the thermostat is near the heating element so even if there is no water the heating element will eventually shut off due to radiant heat transfer. Will the heating element overheat before radiation turns it off? Perhaps. Thus turning on the heat with no water in the tank will not necessarily burn out the heating element. If empty (it almost never is), the EL yellow detergent dispenser tank on the wall will fill in 70 sec. This implies that 1/7 is dispensed per 10 sec. rinse cycle. While the machine rinses both fresh water from the rinse and "concentrated detergent solution" from the EL tank flow into the main wash tank. At the same time, about 5% of the used wash water drains out the overflow from the main tank. Since filling takes about 3 min., almost all of the detergent which dissolves in the EL tank gets into the main washer tank. At this point the EL tank contains only a weak solution so add more detergent (or stir so that more detergent will dissolve). MAINTENANCE & REPAIR The bottom rinse spray arms and the wash-arms may be lifted out to be cleaned. The top wash-arm will come out if the handnut below it is removed. The top rinse spray nozzles are fixed and don't rotate. If someone operated the dishwasher without the filter trays in place, the wash-arms may become clogged with garbage and need to be cleaned. The rinse solution ("Dri_Vac") and detergent dispenser are both made by EL = Economics Laboratory 800-352-5326. Their rep. will try to sell us more modern dispensing equipment which we can't afford & don't need. The vacuum breakers sometimes stick and may be fixed by tapping them. One is just above the detergent dispenser and tends to leak. To fix this one unscrew the top with a large adjustable wrench (note teeth marks on it from pliers). Then manually run the rinse to pop out the internal part (keep your hand over the breaker to catch it as it comes out). Usually just taking it apart and putting it back together fixes it. Perhaps polishing the inside brass cylinder (with a scouring pad) would help. Plumbing stores don't have one. The "electro-lift" (see diagram about half-way thru "Instruction & Parts Manual") is found on the right top of the washer towards the back. It contains a limit switch which may stick when the lubricant inside the switch gets old and hard. To lubricate it one must do much more than just remove the electro-lift cover. Be very careful when taking the switch apart since spring-loaded parts may fly out. The cam and push rod (not the switch contacts) is what needs lubing. If the washer sprays water into the kitchen when the washer door is open, then it's likely time to lube this switch. Check that the external lever (14 in manual) freely returns by internal spring pressure and doesn't stick. If the door is sluggish in lifting up, lubricate its rollers. It's easy to remove a roller for lubrication by removing two nuts. When the tank is not full, the door closed, and the switch on auto, rinse water should spray into the machine to help fill the tank. If instead of filling, the pump motor goes on (a slightly different noise from spraying) and the machine goes thru a wash/rinse cycle without wash water then a possible cause is that the tank electrode is shorted out. Perhaps a food particle is stuck in the electrode tube. This electrode is found on the right side of the main tank at the full water mark but it is partly hidden from view by a tiny metal "roof". Spraying water into it from the garbage disposal sprayer may fix the problem. The local sales rep is Industrial Electric, Cudahay, CA, phone 213-771-7100. The Stero model is SDRA, serial # 1049765. Current price (1991) $6000 +. Stero Co. address: 3200 Lakeville Hwy., Petaluma CA 94952. Use only a non-sudsing detergent intended for a commercial dishwasher. The green rinse liquid in the bottle on top of the washer will always appear full since it's used up by injecting water into it. Replace it if it isn't very green anymore.