Evcon Heater Issues

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  #1  
Old 01-02-08, 07:14 AM
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Evcon Heater Issues

Help….. I am trying to repair an older 1985.ish Coleman Evcon heater running on propane gas.
The problem is that the circulation blower short cycles continually. The reason the Blower is short cycling it the low temp switch keeps cutting out. I believe that the switch is operating properly because if I jumper over it to make the fan run continuously the unit will not provide heat to the from the floor registers. During this time the draft fan is running and I can see a blue/orange flame in the burner chamber.
This leads me to believe that the main blower is cooling the heat exchanger to the point the low temp switch cuts out. So why am I not getting enough heat from the burner? Our propane tank is at 75% and the pressure gage at the tank shows 50psi without a drop in pressure when the furnace turns on. Water heater and stove are both working fine but they do not consume gas at the rate the heater does.
I think my issues is in the burner (clean and to simple to really be the issue) or the control valve, but I am under the impression that short of taking the valve to a repair facility there is nothing I can do or check from here?

Thanks

Mike
 
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  #2  
Old 01-02-08, 09:14 AM
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Originally Posted by mareimer View Post
Help….. I am trying to repair an older 1985.ish Coleman Evcon heater running on propane gas.
The problem is that the circulation blower short cycles continually.

The reason the Blower is short cycling it the low temp switch keeps cutting out.

This leads me to believe that the main blower is cooling the heat exchanger to the point the low temp switch cuts out.

So why am I not getting enough heat from the burner?

I think my issues is in the burner (clean and to simple to really be the issue) or the control valve, but I am under the impression that short of taking the valve to a repair facility there is nothing I can do or check from here?

Thanks

Mike
What are you asking?
Is the heator igniting than going out and the FDB is cycling?
Is the heator blower cycling correctly?
Is there enough heat be produced to maintain temp past blower fan limit?
Are the events that are happening in the rite order?

Propane is very dirty and moist. Does the equiptment have a drip leg installied on the gas inlet? You may have a partuly blocked gas valve or blocked buner.

The (control valve) do you mean gas valve?

On some modles the valves have an inlet screan, this mite be pratuly blocked.

WARNING!!!!!! You are dealing with an explosive fuel shut off supply to unit, or form sourse before attemting to make any repairs or adjustments to these parts. Extinquish any open flames, This includes your cigerete!
 
  #3  
Old 01-02-08, 10:21 AM
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Is the heater blower cycling correctly?

Yes it turns on when the heat exchanger heats up and low limit switch closes, Then it will turn off when the heat exchangers temp drops below the preset temperature. On this unit the control is a simple as that. I did not see any place to adjust lower limit switch.

Is there enough heat be produced to maintain temp past blower fan limit?

I do not think so, the switch will cut out shortly after the fan comes on and “cools” the heat exchanger.

Are the events that are happening in the rite order?

Once again I believe so.

Draft fan comes on to purge the chamber.
Pause
Hot surface igniter comes on.
Pause
Gas Valve Turns on
Pause
Hot surface igniter turns off
Long wait
Low Temp Limit switch closes
Blower turns on.
1 to 2 min
Low temp switch opens
Blower turns off
2-3 Min
Low Temp Limit switch closes again
Blower turns on.

At this point the Temp will rise and fall untill the house comes up to temp.

Propane is very dirty and moist. Does the equipment have a drip leg installed on the gas inlet?

When I installed a new water heater I had to add one at the water heater. I did not think to check if there was one at the heater.

You may have a partly blocked gas valve or blocked burner.

I imagine that a blocked valve in not best for a DIY project. I cleaned the burner assembly and it did not improve the performance.

On some models the valves have an inlet screen, this might be partly blocked.

I will check that when I get home.

I have always been cautious / fearful around propane. One spark and a few stray molecules…..well……

BTW I only smoke when mad and it generally comes out of my ears………………
 
  #4  
Old 01-02-08, 10:57 AM
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I hope no smoke comes from your ears....

Back to bussiness.

There are adjustable limit controls for contorling the low or start fan switch.

Do you have a way to measure the gas pressure at the heator?

The regulator could be bad or blocked..(50# @ tank)

The regulator / gas valve are inexpensiove to replace if needed.

has this always been this way?
 
  #5  
Old 01-02-08, 11:13 AM
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There are adjustable limit controls for controlling the low or start fan switch.

On Most I have seen Yes But on this one I have yet to find them, the switch is a simple barrel that goes into the heat exchanger above the combustion chamber. I think Coleman/Evcon built it as cheaply as possible with a fixed temp on the stupid 13.00 switch.

Do you have a way to measure the gas pressure at the heater?

I would have to cobble up something but I think it could be managed.

The regulator could be bad or blocked..(50# @ tank)

What should it be?

The regulator / gas valve are inexpensive to replace if needed.

Has this always been this way?

It started about half way through the last tank. That is why I will look at the traps and screen filters when I get home. (I don’t always think of things like that, I deal more with Compressed Air and hydraulics, still a problem when they leak but not quite as explosive) It was not a big problem till it got very cold (-5f to 15f) and the heater could no longer keep the house warm.
 
  #6  
Old 01-02-08, 07:18 PM
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Connecting up a manometer to measure the gas input at the furnace would allow you to check for low or erratic gas pressure. Measuring the gas pressure at the burner manifold would allow you to determine whether the gas valve and it's regulator are operating properly or need adjustment or replacement.


Frankly, these are jobs best done by a skilled repairman.
 
  #7  
Old 01-03-08, 01:19 AM
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I would recheck that gauge, make shure it is working.

Do you have an insulating blanket around the tank or a heator on it, these help keep the pressure up during realy cold times.
 
  #8  
Old 01-03-08, 06:34 AM
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The Screen on the inlet filter was pretty clogged, once I cleaned it the flame turned to more to a blue color. I had my wife take the regulator/control valve to a repair man today to get it looked at. If there is that much junk in the inlet side I hate to see what it looks inside.
While I know I can take it apart and clean it, the reassembly and testing is best left to a trained professional. So…..I will let them do it.

Thanks for all of your help.

Mike
.
 
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Old 01-03-08, 07:41 AM
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Is this the screen on the inlet to the regulator on the propane tank? If not, can you describe in more detail to what you are referring?
 
  #10  
Old 01-03-08, 08:38 AM
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When you remove the gas control valve from the furnace there is a screen in the gas inlet side. It was full of small rust like partials. The sides of the inlet were moist and had black greasy gunk on them. It looked like a pneumatic system that had been contaminated by water.
 
  #11  
Old 01-03-08, 08:56 AM
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Originally Posted by mareimer View Post
When you remove the gas control valve from the furnace there is a screen in the gas inlet side. It was full of small rust like partials. The sides of the inlet were moist and had black greasy gunk on them. It looked like a pneumatic system that had been contaminated by water.


Hmmm. Well, that's an unusuak problem. It's quite rare to find debris in those screens in my experience.
 
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