trane xl90 11/89


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Old 11-07-10, 06:23 AM
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Smile trane xl90 11/89

i bought this furnace for a rental and after installing it the (hsi) ignitor will not come on but the blower runs constantly.
iwas told it worked and i could'nt afford a new
any poss.ideas for me to try?
 

Last edited by wesleypierce; 11-07-10 at 06:49 AM. Reason: need to add
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Old 11-07-10, 08:19 AM
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The most like defect is that the pressure switch isn't closing. Use an AC voltmeter to see if that's the case.

Does the pressure switch has two or three electrical contacts?

95% of the time the pressure switch closes because something in the venting system, heat exchanger or inducer motor fan is defective. The pressure switcdh is OK 95% of the time, so don't bother changing that out.


What is the model of the furnace from the rating plate in the burner compartment of the furnace?

By "the blower" do you mean the small inducer motor above the burners or the fan that circulates air around the house?
 
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Old 11-07-10, 10:02 AM
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the model#is tuc100b94ao and the blower that circulates the air ,but the blower above the burner does'nt come on at all . i went and bought a new thermostat anyway.
 
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Old 11-07-10, 10:06 AM
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trane xl90

what should the voltage be coming out of the switch?
i sure hope someone can help ,otherwise i might have to resort to getting a service call. and the pressure switch has two terminals.
 

Last edited by wesleypierce; 11-07-10 at 10:11 AM. Reason: adding text
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Old 11-07-10, 10:36 AM
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The sequence of operation when the furnace lights up is that the thermostat calls for heat, then that small fan motor above the burners should switch on. When that motor comes up to speed the pressure switch verifies that the vent is working properly and turns on the hot surface ignitor.

Since the inducer motor isn't turning on, we don't have to deal with the pressure switch.

The motor for the fan is on, so you have 120 VAC power to the furnace.

Use an AC voltmeter to check to see if you have 24 VAC at the R and W terminals when the thermostat is turned up. Connect one terminal of the meter to chassis ground and measure the voltage with the other test lead.

Don't replace the thermostat. If it's not the problem perhaps you can return it.
 
 

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