big waynester

I have an Armstrong Ultra SX90 and what it was doing is it would run (heat) fine then all of a sudden it would blow cold air. I would turn the heat switch on and off and it would run fine for a while. No it won't even fire up. I hear a click noise and that is it.

SelfContract

Check thermostat first. Maybe defective. Then check pilot, then 24v transformer, or gas valve control in that order.

HeatPro

The most common problem is a need to clean the ignition sensor.
http://www.heatpro.us/service/ignitor.htm

big waynester

I cleaned the sensor, I got it to fire but it still blowc cold after a while. I am going to try a Thermostat next.

HeatPro

You don't need a thermostat to do that, you would take the two wires on the thermostat that make the furnace run and join them together or remove the wires that come from the thermostat to the furnace to jumper the terminals you take the wires from at the furnace that come from the thermostat. If the same thing happens, you saved buying another test instrument called a new thermostat.

randomkiller

I have no idea why so many people have issues troubleshooting a furnace and the guys that try and do it without a meter just kill me. Do yourself a favor and don't guess what part you think is bad without doing some troubleshooting with a meter.

No heat, first check to see that the t-stat is set high enough to call and is in the heating mode. Next check to see if there is line voltage at the furnace, often an emergency switch is off.

There is a schematic on the inside of the blower door more than 95% of the time. It shows the contacts in the non powered position, so they will be in the opposite position when powered.

If you think the thermostat is an issue and you don't want to check it with a meter, put a jumper wire on the "R" and the "W" terminal at the furnace and that will eliminate the t-stat.

In most furnaces with a draft inducer, the call from the stat brings on the inducer, the inducer when up to speed makes the contacts in the pressure switch, which sends power to the ignition control board, the board makes a relay that sends power to the igniter and then the pilot valve after a time delay, if the sensor is able to send a current (milliamp) back to the ignition control the main gas valve is powered. The indoor fan either comes on by a time delay in the board or by temperature sensor (fan limit) in the furnace.

Sometimes on 90% plus furnaces the condensate pump has a float switch to cut out the power to the control board, the pump outlet can freeze up if it terminates outside the wall, causing the pump not to discharge.

If the t-stat is jumped out and the inducer is running but nothing else, check your safeties (limits) there are usually several, one near the top of the furnace(high limit), one over the burner rack (roll out), one or two on or near the blower squirrel cage. The high limit usually has a manual reset (small button). If any are open you won't get power to the control board.

You can't use a non contact volt meter to do any troubleshooting on a furnace.

The humidifier transformer should not be powered off of a motor winding.

Don't plug a modem into the outlet on the side of the furnace this creates havoc with many igniton boards as does talking on the cellphone as your troubleshooting.

I hope this helps some of you guys out.

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neolitic

Anyone remember this guy?
http://www.contractortalk.com/f6/carrier-58gfa-furnace-problems-2226/

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(Sorry....it seems there really are dumb questions)

HeatPro

Can you get a cheap $7 thermostat any more? That's the favorite DIY test instrument. It seems a LOT cheaper to get a $10 VOM than a $30 electronic thermostat test instrument. But then, it doesn't have them handy letters like R and W that might mean colors if the wires in the wall don't have black and yellow.

big waynester

The furnace has been running some what OK. It seems to start all the time but the time varys before it starts blowing cold air, sometimes an hour, some times all day, when I turn it off at the t stat then turn it back on it "resets" it and starts blowing warm air again. What I just did is tape the switch on the door so when it starts blowing cold air I can take the panel off and look at it, my question is what should I check when it does this.. thanks.

HeatPro

When an ignition control doesn't sense a flame, some after a few tries, it locks out. Turning the power off for a while resets it when it is turned back on. There is a reason the control locks out, but it can't be observed from here.

hf05

i believe you have a s86 honeywell ignition module on that unit.if 24 volts is present on that marked terminal this is probably your prob.hard to troubleshoot this way but when you said u had a click and no flame ,module not producing spark to lite pilot burner and start sequence.

HeatPro

It can be as small a problem as bad contact between wires or between a molex connector. Normal service is to clean and tighten all connections.

big waynester

OK back to nothing again, jumpered the red and yellow off T stat-nothing, checked voltage at T stat connection on furnace ( where else to check?) and I am getting 28.7 vac. HF05 it reads honneywell SV9502

big waynester

I found a bad solder connection on a resistor, going to try to resolder.

hf05

thats your gas valve.pls see if you have a grey box full of wires on the right side wall or bottom ,but then again your click may have been your valve not opening.if u have said grey box this is module and most likely your prob,

vlux

dont mean to be rude but you dont know what youre doing, we said jump the red and white wire, not red -yelow. dont blow yourself up or we all loose

Tin Cup

sounds like a bad knute valve. pronounced "kanoot".


Tin Cup

TNHVAC

You may want to check your gas orifice for obstructions. I recently had a call on a Carrier dual-fuel (3 years old) that the installer replaced some sort of relay on last winter (according to the homeowner) still same old thing. Homeowner endured all last winter with no heat while outside temps below 35 degrees. Called me this year,what I found is bug pieces in 2 of the 3 orfices. The flame sensor & the igniter both had some blockage. Hope this helps.

briandurussel

Check out the flame sensor or Ignitor combo flame sensor. There is what is called flame rectification, if is cannot recognize the flame it will not keep that secondary open on your gas valve leaving cold or just "air" blowing. Also check the board and terminal for wear and tear, check the board especially for moisture or water marks. Flame rect should be around 2-4 microamperes.

Leo D

Need help too:
My Armstrong Ultra SX-90 Furnacehas a problem:
here is what happens
1 power vent blower goes on
2 hear a click and ign lights and burner lights
3 after a second hear a click and burner goes off
4 after another second burner lights again and then click goes off
5 when I shut off power to unit and reset, it might work for a cycle or 2
Thanks for any help