Reminds me of an experience I had with some bathroom faucets I replaced.
Stopped by the local high-end plumbing supply store to see what the diff was between the ones I had bought at KMart or someplace like that and the ones they had.
Showed mine to the guy behind the parts desk and asked "What's the diff...?"
He looked at me, looked at the faucet, pointed to a functional equivalent by Delta for about 10 times the price, turned red in the face and semi-shouted "This is *QUALITY* and that is *SHIT* !".... I mean like other customers in the place turned their heads.
Went home, installed them.
That was 37 years ago.
In that time, I have rebuilt the fancy-schamcy Delta faucet on the kitchen sink a total of 5 (five...) times.
The "Shit" faucets in the bathrooms ? One is still going with no maintenance. The other, I replaces the cartridge last year because the action was getting stiff.
Well, I stalled around the last two months of last winter and the first month of this winter, about installing the primary control unit for my furnace, and finally did it two nights ago.
Now it's starting to appear that it was not bad in the first place, that the thermostat contacts have excessive resistance.
It chattered for 60 seconds before it started Sunday night, but it's been so warm since then, it wouldn't have gone on.
At least I didn't pay for the control unit, got it free from a matching furnace that a neibhbor was replacing.
I'm still surprised that a 24v typically-low-current thermostat would have high resistance contacts tthat would lower the voltage to the relay.
There's no sense in rushing into things. I bought my present cave when it got too cold to live comfortably in the back of my pickup. I figured it was cheaper than paying rent all winter in a tight rental market and I'd move on in the spring. That was 26 years ago...
I just checked and with the furnace running, there is between 1.6 and
1.9 volts AC across the thermostat heat terminals (red and white). Out of 24. That really is far too high, unless someone can give me a good explanation.
Late last winter, I thought something had happened to the relay magnet to make it weaker. Sometimes if I pushed on the armature and got it close to closed, I could hear it click when the electromagnetism pulled it the last millilmeter or two. Even though it wasn't enough to close the relay without my help. But it wasn't the relay, it was voltage, lowered by either bad wiring or a bad thermostat, and I doubt it's the wiring.
Some things start as trial, but end up working. In the housing situation, I bought a mobile home, figured to get a real house some day. Twenty year later, the economy is tragic, and I'm in the same place.
Yes. That's why it's far too high, right? It should be zero or close to it.
I haven't measured that, except when the relay was chattering.
But the cover is off the control unit and the voltage between the R and the other end of the 24v xformer is 27.2 volts AC. With the thermostat calling for heat, the voltage between W and the same end of the xformer was 25.6., a 1.6v difference.
When I went to measure the voltage between the R and the W, even with a digital meter, the relay stopped chattering immediately and closed. At that time the voltage between R and W was 1.9 volts.
I should have said that the thermostat in the wiring diagram that came with the furnace did indeed have an anticipator. That's not the thermostat I've been using, but maybe it has one too.
And I can see now what you mean, that the resistance of the anticipator would lower the voltage to the control unit.
But it shouldn't lower it so much that the relay chatters and takes a full minute to latch. With the previous control unit, the relay didn't chatter -- it totally failed to close, until I put a weight on the armature, and then as the armature went down, I could feel the magnetism of the relay pull it the last millimater or two, and I could hear it click. And iirc I could remove the weight and it would stay closed until the thermostat turned the heat off.
I think I incorrectly concluded the relay was bad, perhaps shorted windings that made it not as magnetic as it should have been, so I replaced the conrtrol unit with my spare, and the new one is acting similarly, but it chatters.
It seems to me the voltage must be low, but it starts at 27vac which is fine for a 24v xformer. And I have to admit that losing 1.9v, whether that is normal or excessive, still leaves 25.1 or 25.6 volts, which ought to be enough to close the relay, right?
So what do you think is going on?
Does chattering mean that as the armature closes, something happens to lower or interrupt the voltage that is closing the armature, and then when it opens fully the voltage is restored? And that something would normally be the load when the relay closes, except here the load, the furnace oil-pum/blower-motor and the furnace sparker, is straight from 110v, nothing to do with the 24volts.
I think he knows it's across a closed switch - and he has a 1.9 volt drop across the "bad" points in the thermostat. However, he is forgetting there is an "anticipator" in the thermostat. This is a resistor in series with the contacts. He should check the anticipator setting, then try it with the adjustment fully one direction, then the other - and see what happens.
He also needs to check the voltage across the transformer secondary with the furnace running.to be sure the trasformer is not weak (which is my suspision.
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