Lately, my electric heating unit is blowing cold air for awhile after it turns on. I have check the three heater coils, and they are all putting out 240V. The only thing I can think of, it that the coils are suppose to preheat, and they are not.

Does anyone know.......? Also, by looking at the pictures below, can you identify the parts for me?

#1

#2

#3

 

It's been my experience with electric furnaces, not much can go very wrong.

You do have 240 across each element?

You may have a thermocouple failing, those are the items with the E146 on them. If one is open, the element will not heat up. You may still read voltage because of feedback. Best way to tell whats going on, Ohm out each element seperately. Should show nearly zero ohms if they are in fact good.

Make sure to turn the electricity off before unplugging the elements.

Ed

hope this helps ya.

 

#2


Right off, the three things in the middle are the actual strip-heat sections. They can be rated at up to 5Kw each. yours can be good for up to 15Kw pending the actual rating (they can be lower).

The two relay looking things on the right are sequencers. On a call for heat, they bring the individual stages on in increments. That way your not banged with a big electrical surge with them all coming on at once which would pop more realisticly valued fuses/breakers.



#3


In the center of each strip-heat component, those devices with two wires connected are temperature activated switches. Should any one element run at too high a temperature (such as a failed indoor-air blower), these will open and interrupt the power to the strip.

On the top left, that's the 24vac control transformer. It provides the control voltage to run the whole thing.

Below that is the relay that switches on and off the indoor air blower.



IIRC, the fan is turned on pretty-much immediately with a call for heat.


While you may have 240vac available to the heat elements, that doesn't tell you if they are actually working. They may be burnt in two. Short of pulling them out for a look-see, you need an ammeter to read the actual current draw of each. No current draw means an open element.


Hope this helps.

 

Thanks for the quick replies. Very educational answers.

I have used a volt meter to check the current on each side of the elements, and got 240V on each. If I understand correctly, it will still show voltage even if the element is bad...? I guess the next step is to pull the elements out and see what they look like.

Thanks again,

 

Correct!

As mentioned above, be sure to remove all electrical power at the breaker box and most likely there at the furnace (safety disconnect).

The following image is of the typical strip-heat element assembly ~

 

turn the power off to the unit.
set your multimeter to ohm (greek omega symbol)
disconnect each element, and see what kind of resistance you get. If one ready O.L. or much higher than the others, its bad.

 

Thanks again,

It's too dark in there to fool with tonight, but in the morning I will turn the breakers off and ohm out the elements. This thing is so old, I may just go ahead and take them out for a look-see.

Boy, this site sure can be educational.

 

I'm not an electrician or a HVAC guy, but my electric furnace has always done this. The fan blows room temp air for 5-15 seconds before the heater elements are energized.This would be a safety feature in my mind. If the grids heated before the fan kicked in, and the fan failed to start, the grids would overheat quickly and create a fire hazard. So they are wired so that the blower starts first, and once it is running, the grids begin to heat up. If the fan doesn't start and run, the grids won't be energized, so no overheating can occur.

High efficiency furnaces burning fuel oil, propane or natural gas do much the same thing. The exhaust fan runs and "purges" (their word, not mine) the heat exchanger, then the blower fan comes on just after the igniter lights off the main burner. The one in my fiver does this too.

If I misread your problem, my apologies. If not, I'm not sure you've got a problem.

 

Thanks greatwhite, what you say makes sense.

Mine runs for a lot longer then 5-15 sec before it starts to warm the air coming out of the vent. Once it starts getting hot, it does quite well and gets the house up to temp pretty quick.

My TT also has the "purge" cycle before the burner comes on. That was good thinking on someone's part.

 

Could it be that the fan is just pushing the cold air that already in the vents (ahead of the stream of warmed air) out, and warming those cooooold vent ducts?
Like when you turn on the Hot faucet and have to wait for the warm water to get there.

 

Up until lately, it pushed the cold air out in about 10-15 sec. Now it takes it much longer. Even though I get 240V across the elements, the more I read here the more I lean toward burnt out element(s). I'll know here in a couple of hours............

 

Good Luck, be safe.

 

Thanks, I will.

The way my luck has run lately with plumbing and water heater problems, I have decided to wait until Tuesday to work on the furnace. It would be just my luck to get it apart, break something, and then be without heat until Tuesday.

I'll report back when...............?

 

Lordy, Lordy! What next!

So, I decided to let the furnace go until Tuesday. A while ago my wife came and told me there was water around the bottom of the washing machine. Sure enough, on the spin cycles, there was quite a bit of water coming from underneath. Pulled it out (it's in a small closet of a side hallway) and it had been leaking long enough that the tile was coming up and the baseboards were coming apart. The washing machine is out by the curb, and the fan is drying things out.

I'll be glad when this year is over! The Friday before Thanksgiving, my back started bothering me. That night, I made my first ever ambulance ride to the emergency room.....totally incapacitated. Turned out to be a "cocked" vertebra and two ruptured disk. Then, "THE HOUSE" problems started....first it was a stopped up drain in a bathtub. While I was working on that, the toilet stopped flushing. Well, I thought, changing the post in the tank wouldn't be too hard on the back......wrong again. When I went to turn the water off at the wall, the valve broke and made a pretty good mess before I could cut it off at the curb. Lying on the floor working between the tub and the pot to fix it almost done me in.

That's not the end.........last week I got my electric bill and it had more then doubled from the previous month. I got to eliminating heavy draw appliances and found that the bottom element on the hot water heater was not working, causing the top one to run almost constantly to keep the 50 gal tank hot. After a few calls to GE, they emailed me the thermostat trouble shooting instructions. I replaced the top thermostat to fix it, and went ahead a replaced the top element.

Now let's see......screwed up back, stopped up drain, broken toilet, broken hot water heater, limping furnace, leaking washing machine and ruined tile and baseboards in the wash closet. I sure hope the "bad" ends with the old year.

NOW, the Cowboys are playing like crap!

 

good luck.