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Hello, this is called an anticipator. Think of it as a little electric blanket for the thermostat. The anticipator either lets the stat run cooler or warmer which results in different run times.
You see, the thermostat does not know how big of a furnace it is hooked to. So if you take a reading of the gas valve, you can move the pointer to the appropriate number to match.
If you didnt have this the and the thermostat was set for 70....it would leave the gas valve on until it was 70 degrees at the thermostat, then the valve turns off, but the blower still has to get all the heat out of the furnace. So really we overshoot 70 by the time the heat is cleared out.
So the "anticipator" anticipates when to turn off the gas valve by either warming or not warming the stat, so that by the time the furnace heat is purged you should be close to temp.
When the arrow says "longer cycle" it turns the electric blanket down thus letting the furnace run longer. Sorry to ramble so much.
So I should look on the valve - I'm trying to use less gas so I should set it to .4 or .5. There is another brass color thing above that, that seems to be set in the opposite direction of longer. You didn't ramble! You were trying to explain! I just want to be clear! Thanks
One thing some techs do is actually take a amp draw and set the anticipator according to that. Others look on the gas valve and you will see a small print of an amp reading, and then put pointer to that. If you ever have a thermostat set for 70 but it reads 72 in the house, odds are the anticipator is set for longer cycle. If the furnace always seem to kick off a bit early it means the anticipator is warming the thermostat quicker and shutting down early.
Thank you - it's sort of the opposite. Let's say It says it's 68- but it feels colder so I have to set the thermostat to about 80 before it comes on. It heats the apartment quickly, so it seems I have to turn it off. Shouldn't it do this itself? If so - I'll have to tell the building owner, I guess! I thought they turned themselves on and off when you set the temp - maybe this one's broken. But I will try and see the gage number. They are outside working on the building - and should be able to help! I hope!!! Thank you for your help-- this is a great site!
Since you have the older style thermostat instead of digital it could also be out of calibration.. Like a speedometer in a car... Does it really match? You most likely have an out of calibration thermostat.
Can I calibrate it or should I let the men do it.