Air tanks can rust on the inside due to moisture in the air that is stored in them. And there was a big thing about bad electrolytic capacitors that were made in the orient about 10 to 20 years ago. I have personally repaired several TVs and some computers as well as a bunch of other electronic items by simply ordering all the electrolytic capacitors in them and changing them wholesale. They were relatively cheap so I did not waste my time testing each one of them. In virtually every case, that fixed the item. My point is, these parts can go bad.
That being said, I suspect you are correct in stating that these guys were scam artists. New parts should be packaged in either the OEM's packaging or in some other kind of package, most of the time. Even the generic capacitors that I purchased from reputable electronic supply houses were packaged in their bags or envelopes.
Yes you are correct about bad caps. We've seen computer motherboards, monitors and the like with swollen or leaking caps. The starting capacitors I have not seen that much. Usually they just dry-up and quit working. Obviously the repairmen probably had no way to check the caps to see if they were good or not. The best way to check a cap nowadays is with an ESR meter.
Sure, electrolytics go bad over time, particularly in hot conditions -
but these mains voltage running caps are of a different breed: metal foil or metallized paper or ditto propylene.
(Starting caps can be of a non-polarized electrolytic type though- as they generally need bigger capacitance than
the MP or PP types can provide.)
Nothing much in them that can go bad or evaporate over time, and they're designed to sit on a lukewarm motor,
and also for having self-healing properties for when the dielectric breaks down somewhere.
One of their crucial properties is, that these in a failure won't short out, merely burn a tiny hole in the metal.
It takes a lot of flashovers to seriously degrade the capacitance on one of these.
And in this application, the cap's value isn't that critical, as the mere mfg tolerances are of +/- 5 to 10 % anyhow.
So the hardest job in putting an old, grimy, dinged one to work in an appliance like this,
is to convince the buyer of the "sheer need" for it (and just how little the provided one would cost,
relative to a new branded one).
Sure this is a scam - where the repair man voluntarily corrupts himself just for a couple of bucks... Poor guy.
Last edited by DIYSwede; 10-09-2019 at 03:04 PM. Reason: Added info on cap types and their uses
Checking capacitors in the field, especially A/C caps is tricky at best. I have a couple different testers and they frequently disagree about the quality of a cap. If I suspect a bad cap I will replace it normally rather than try to test. it. They are cheap and common enough to keep spares with you. My good cap tester is a bench mount and can test at operating voltages up to 10KV. If you test with a multi-meter or ESR meter etc. the voltage is not high enough to really test leakage. If I were in the business I would change them out and test them at the shop.... or just toss them. In the grand scheme of things a $10 cap is not worth messing with, replace it and be done. Not as bad as replacing blinker fluid on your car but close.
I too have noticed a bunch of bad caps on the market. Before I retired we were replacing them wholesale in some equipment that had faulty caps from the factory.
Thanks Sleykin for pitching in!
I tried to find some logical explanation why the repair guy offered his personal (seemingly recycled) spare to tsbrownie.
I've done my share in faultfinding mostly vintage radio & HiFi gear, ("boat anchors", as well as solid state)
and lacking the commercial test gear you mention, have thus devised a few Q&D "instruments" of my own:
Electrolytic "reformer" variable PSU:
1) Slowly taking a stored electrolytic cap up to its nominal voltage at a low (< 5 mA) current:
2) Then slowly taking it up to its surge voltage, whilst carefully monitoring for current hogging.
It should ideally, really smoothly go up to Vsurge only - otherwise discard.
3) At Vnom - crudely testing its leakage by putting a neon lamp ( w appropriate series resistor for that voltage) to ground,
waiting for intermittant flashes from a bad cap at nominal voltage, and then also at its surge voltage.
Cheap, fast enough and optimised method for maximum longevity of the (fairly expensive) caps and the gear.
just 2 cents
Further reading for "so inclined":
(The latter plugging their wares, but the reasoning in the initial paragraphs can be enlightening)
Hmmmm. I think I need to push back a bit.
In the first instance, I can’t speak to the need or compulsion to replace what appears to be a reservoir canister.
In the second instance, I can add some info. The first two components he references are a legitimate part of a refrigerant-loop device that involves resistive-start compressor. These devices do fail, are very low in cost, and are part of a normal repair event.
The third item he talks about is a capacitor, as referenced above. These are a part of a refrigerant-loop device that requires a capacitive-start compressor. This is separate and distinct from the other equipment he discusses. The start-caps *do go bad *. They are of little cost or value. They are not manufacturer-specific and do not derive added value through a brand or label.
A competent service technician will replace a start capacitor as a part of a service call for a refrigerator/freezer/air conditioner/ice maker as a matter of course. In a service call of this kind with a trip-charge of $60-80, replacement of these parts adds scarcely %10 to the total cost and can stave off a future call.
He was going to charge me $30 for a capacitor that was clearly second hand (you could see where it had been mounted before). I don't think I mentioned it and should have, but he was trying to show me with his multimeter (with no cap setting) on the ohm setting how it might be bad, but the readings across all the caps he had and mine were the same.
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