Transformer/Thermostat

HotRod1975 · October 20

I have a Dunkirk SERIES PSB-6D checked my 24v transformer and it’s only receiving 18v can that cause my Emerson 1F-70 to continuously call for heat? And any suggestions on a comparable thermostat? Is the Emerson 1e30N a good swap?

Thanks

pecmsg · October 20

where did you measure the voltage.

Did you measure the incoming

voltage?

HotRod1975 · October 20

I measured it at the transformer and thermostat wires both receiving 18v

pecmsg · October 20

What terminals it takes 2 points to measure

and incoming voltage?

EBEBRATT-Ed · October 20

At the transformer terminals you should get 24volts all the time. Anything below 21-22 volts is suspect.

You can't read volts at the thermostat unless you have an R and C wire. The thermostat is a switch not a load

EdTheHeaterMan · October 20

I believe that @pecmsg wants to be sure you are measuring the 18 VAC. at the proper terminals. LIKE THIS:

On the left diagram you should be checking the transformer R and C terminals, with the thermostat calling for heat (solid leads) The thermostat should be checked at the thermostat location with the thermostat not calling for heat to get the voltage reading using the R and W terminals at the thermostat.

Some transformers on some steam boilers have up to 5 terminals. You always want to check at R and C

Also did you check the incoming voltage to the transformer? Right diagram if that transformer gets less than 120 VAC coming in then it will hhave less than 24 VAC coming out.

mattmia2 · October 20

My mom's house had a white rodgers programmable thermostat from the late 80's that when I ran the furnace off a generator would read a different temp when the blower would turn off and the voltage and frequency went up slightly. It would finish a heating cycle, the blower would turn off, the power would change slightly and it would decide it was colder and time to start another cycle.

If it is actually 18vac and you are reading ac rather than dc and the voltmeter is accurate, I would look at the voltage coming in to the house, the voltage on both legs of the panel and the connections on the primary of the transformer. If you have a bad neutral the voltage of one leg to neutral could fall enough to give you 18vac.

pecmsg · October 20

bad Neutral like this?

mattmia2 · October 20

https://forum.heatinghelp.com/discussion/comment/1868570#Comment_1868570

I was thinking at the service so one leg to neutral would fall below 120v and the other would go above 120v depending on how well balanced the loads on each leg are

pecmsg · October 20

same thing, i was getting 88 volts at the receptacle, not enough to run the freezer.

Jamie Hall · October 20

Ah… if you are checking at the service entrance panel…. more than a volt or two difference between the two legs and the neutral is a problem. Ditto for the busses in the switchgear. But if you have a heavy load on one leg but not the other, you might see as much as a five volt difference out in the far reaches at a remote panel, such as a barn a couple of hundred feet away…

A heavy load on one side may drop the voltage at the load a few volts, as well — but it shouldn't change the voltage balance at the panel.

HotRod1975 · October 21

measured it wrong. Thank you guys!! Getting 24-26 amps.
now trying to set up my anticipator on thermostat to the right setting. Any suggestions?

109A_5 · October 21

Typically the starting point for the heat anticipator setting is the actual gas valve current.

EdTheHeaterMan · October 22

What thermostat are you using that has a heat anticipator? The oldest 70 series thermostat I can find on the web is the 1F-75 and that one is digital no heat anticipator in that one.

If your thermostat is like the one shown in @109A_5 Post with the mercury bulb on a bi-metal coil then that is the old school heat anticipator. To check the current draw on the thermostat circuit you can use an amp meter to see how many amps the circuit draws during a call for heat. If you have an electronic ignition control, that may draw more amps on the trial for ignition (Start Up) portion of the call for heat, then drop down to something less than that for the operation portion of the cycle. You wan to know what the actual amperage draw is during the operating portion of the call for heat , not the start up portion of the call for heat.

Here is a diagram of how to use an amp meter when the lowest scale is not low enough for a proper reading. You can make 10 wraps of thermostat wire (yellow) around the clamp and read the amperage of the thermostat circuit., then divide your total amp reading by 10.

109A_5 · October 22

@EdTheHeaterMan

https://manuals.plus/emerson/emerson-1f70-series-autometic-set-back-set-up-thermostats-manual

EdTheHeaterMan · October 22

That's the one I thought it was. Installed many of those in the 1980s

Transformer/Thermostat

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