Help with a Presidential electric furnace

[Legal Concepts]

Symptoms: The Digital Thermostat reaches desired temp. blower shuts off, however the heat element stays on.

I can tell it's on, because the sheetmetal is still warm after the blower has been off for quite some time.

It is just a Coleman Presidental, the trailer was built in the 70's. I am thinking somthing mechanical has failed, I suspect the relay that turns the heater element on/off is sticking or malfuntioning?


I don't think it is a thermostat issue, since the blower shuts off, the heating element should shut off also.

I have not peeked inside, so I am not sure how it is wired.

[HayZee518]

the heater elements come off a contactor driven by a control circuit - probably 110 volts or a 24 volt control circuit - may be even 12 volts in a trailer. RVs use 12 volts to operate the absorption refrigerator. and lights. the heater may be propane and uses a flame rod to detect the presence of a pilot flame which operates the main valve. check this out first.

[Legal Concepts]

No propane involved, all electric, this is one of those "all electric" trailers.

[Legal Concepts]

If this helps, whenever it malfunctions(the heating coils stay ON after the furnace shuts off) I can throw the breaker OFF, let it set a few hours, and turn the breaker back ON, vola it works fine....

[Legal Concepts]

Finally the silly thing is staying on all the time....

So I open it up and I got my eyes on those relays.

So I am thinking of checking the Voltages at those relays to see if one is stuck open.

so I just set the DMM to AC and one probe to ground and the red probe to the supected wire? and read the voltage

Or do I do a continualty check of the relays?

The first method would be done under HOT wire conditions, but would the second method tell me if a relay is stuck/shorted open with certainy?

[Java_Bob]

well if it is then it closed, contacts burn melted together... check the coil input if there is none and its still heating i would change out the contactor they are fairly cheap. just match the coil voltage and amperage its propably just an definite purpose type. good luck

[lw@buyerbewareinc.com]

Electric furnace element doesn't turn off

The first thing you need to do is make sure you have a problem.

Electric furnaces use heating elements similar to electric ovens. The elements extend into the air stream passing through the furnace from wiring connections in the wiring compartment. If you open up the wiring compartment, you can see the ends of the elements where wires connect to provide 240 volt current to the elements. It would be easy to check for 240 volts across the element terminals with a voltage meter, but checking is not safe for a person not familiar with electrical wiring.

If you are not knowledgeable about electric wiring and do not have a voltage testing device, I suggest you check to be sure the element is actually still getting power (and generating heat) by using your electric service meter.

If you turn off all the circuit breakers in your electrical panel, the meter will stop turning. Check to be sure it does. Next, turn on only the circuit breaker(s) for the electric furnace. The meter may turn very slowly since a transformer in the furnace uses current to power the thermostat. If it starts turning quickly, you may have an element using power right then.

Turn up the thermostat and run the furnace through a heating cycle. Check the meter speed while it is running. The elements in an electric furnace are typically 5,000 watts each. This means they use 5,000 watts of electricity every hour they are on. The number of elements in your furnace depends on the size of your home. Your furnace could have from two to five elements.

Turn the thermostat down to stop the furnace cycle. If the meter drops back to a very slow rate of rotation, it is likely you are feeling residual heat from the elements rather than heat being generated by an element that remains on after the furnace shuts down.

If your meter turns at a rate that would advance it 5,000 watts in an hour with nothing but the furnace breaker turned on at the electrical panel, you have an element in the furnace that is not shutting off.

Another safe way to check for an element not shutting off would be turn the thermostat way down or even off overnight. It is winter, so that may not be practical. If you can turn the furnace off overnight, any residual heat will be gone in the morning unless, as you suspect, there is an element on when the furnace is off.

I don't suggest you attempt to check for voltage at the element connections inside the furnace yourself. Power would have to be turned on to the furnace after you open up the wiring compartment. This exposes live connections with high amperage disconnects that are dangerous if you are not familiar with electrical wiring.

If you determine that one of your heating elements is remaining on, you should be sure the person you call for repairs is familiar with Coleman furnaces. A good repair service person should carry replacement parts with him so he doesn't have to charge you for more than one trip to the house.

If you have any questions about these suggestions, please ask.

Loren
lw@buyerbewareinc.com

[Legal Concepts]

This is a puzzler, I got a Coleman Presidential 6806 3 heating element electric Furnace.

This is what it is doing....
The Digital Thermostat reaches desired temperature, then the blower shuts off.....but the heating elements stay ON.

I verified this as 1/2 an hour after the furnace has not ran, heat can be felt coming out of the furnace intake.

I shut off the furnace breaker, and after a few hours I turn it on, VOLA! problem gone, for now.

....After a while, I will discover the problem again, shut down the circuit breaker for a while, problem fixed.

...then again...and again etc.

But then just last week(the dead of winter) when the furnace is at it's peak use, it did this again, but this time shutting off the power didn't fix it!

So we investigated, I was thinking "Relay" since I know a furnace from 1978, mechanical relays fail, I figured maybe a sticking contact?

Now yesterday the Furnace blower was kicking on for 10 seconds then shutting off, 4sec and the furnace started back up, over and over.

I headed to the thermostat, turned down the kick-on temp, nothing, I even selected "Off" at the thermostat, the furnace just kept running! So I Hard rebooted it at the circuit breaker.

I figured I would take a multimeter and Kill the power to the beast and see if one of my contacts was sticking open or something wrong with a relay?

However it appears to be "fixed" again so I dunno what is going on!

I don't think my problem has anything to do with the Blower, because once the Thermostat reaches the right temp, the furnace 99% of the time, the blower shuts down, but the heating elements are still going...