Limit switch problem


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Old 11-23-09, 11:29 PM
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Limit switch problem

Thank God for DoitYourself forum...I certainly ask my share (and then some) of questions and appreciate all the help.

I have a Carrier Gas Furnace, 11yrs old and it has a new filter, there's no blockage in the cold air return.

Here's the problem:

In order to get the furnace to work, I have to turn it off, then back to on and it goes through one cycle fine, but then I believe it's the limit switch that shuts it off and it doesn't come back on.

To get it to come on again, I have to turn it off, then turn it back on...goes through one cycle, shuts off.

Does that sound like a limit switch problem?

thank you for your help!
 
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Old 11-24-09, 01:20 AM
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Originally Posted by RMCHomeowner

To get it to come on again, I have to turn it off, then turn it back on...goes through one cycle, shuts off.

Does that sound like a limit switch problem?

thank you for your help!


No.


Generally speaking, limit switches reset on their own and the ignition process begins again when they do.


What is the model of your furnace, which can be obtained from the rating plate in the burner compartment of the furnace.
 
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Old 11-24-09, 11:42 AM
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(I think these are the numbers)

Model # PAV-58

Size 110k BTU

115 volt


We put a new thermostat on it and it didn't work.
 
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Old 11-24-09, 12:03 PM
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The manual on your furnace is available here:

http://www.xpedio.carrier.com/idc/gr.../58p,r-1sm.pdf


When the thermostat signals for heat, the inducer motor (the small fan motor on the front of the furnace with the cage around it) should start up. I take it that is not happening.

If you have a multimeter that measures AC voltages, I'd test to see if you have 24 VAC at the R terminal on the circuit board, and on the W terminal when the thermostat is turned up.

If you do, you should check the inducer motor electrical connection to see if you have 120 VAC at the connector going back to the circuit board when the thermostat is turned up.

It does not sound like the limit switch is the problem at this point.
 
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Old 11-24-09, 07:14 PM
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Your 1998 58PAV furnace should display a trouble code visable though the furnace panel. What code is displayed when it stops heating?

 
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Old 11-24-09, 07:55 PM
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Houston,


I don't think this furnace has a diagnostic light.

None is apparent on the illustration of the ignition module in the manual I posted, and there is no viewing port in the fan compartment cover on the picture of the furnace in the manual.

I think this is the same circuit board as is in the Carrier CAV model furnace, which does not have a diagnostic feature.
 
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Old 11-24-09, 08:59 PM
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Your manual is very old. Carrier added the LED mid 1993.

This is a 1996 manual...
http://www.docs.hvacpartners.com/idc...58p,r-13sm.pdf
 
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Old 11-24-09, 09:02 PM
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We can see that the light shows # 13 one short and three long with LED light.

The motor wheel is tightened, the filter is brand new, the returns are clean and no blockage, so that would leave the blower motor start capacitor or the open flame roll out switch.

The motor it's self runs fine and doesn't make any noise when it's on.

What is a open flame roll-out switch?


What to do next?
 
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Old 11-24-09, 09:15 PM
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Probably a dirty evaporator coil or bad capacitor.
 
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Old 11-25-09, 07:14 PM
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We got a new capacitor, put that in and now the LED light blinks 3 and 3 instead of 1 and 3 and it does the same thing as before,...cycles once and doesn't come back on.

So, where is the flame roll out switch? What is it and where is it located?


The Bell Plumbing people said that they would have to order special parts like that, if that's the problem.

What do the flame roll out switch's usually run in price?
 
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Old 11-25-09, 07:51 PM
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The flame rollout switch is a manual reset safety.
Resetting power would not reset this.
A dirty evaporator coil is more likely than a faulty hi limit.
I would at least look at it before buying a new limit, (or have someone inspect it for me).
The limit switch (LS) is between PL1 pins 1 and 7 (red wires) .


The inlet side of the evaporator coil is covered by a triangular piece of sheetmetal. Kinda tough to access...


 
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Old 11-26-09, 03:14 PM
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THANK YOU!!! I believe that was the problem. It needed cleaning out alot!

Now, it's running full cycles and not shutting off---unless we turn it off.

Problem solved!
 
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Old 11-26-09, 04:44 PM
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You are very welcome

Happy Thanksgiving
 
 

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