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-   -   York Stellar Plus NG furnace wont' stay running-HELP (http://www.houserepairtalk.com/f8/york-stellar-plus-ng-furnace-wont-stay-running-help-5650/)

johnceberhardt 11-29-2008 01:11 PM

York Stellar Plus NG furnace wont' stay running-HELP
 
York Stellar Plus Natural gas furnace, I bought the house about five years ago so I donít know exactly how old it is. It is small; only heats back half of house and that consists of only a few rooms.

Sticker says model # P1UDD06N03801A York Stellar Plus Natural gas furnace for furnace.
Situation:
When heat is switched on, the small motor starts running, the pressure switch closes, the igniter ignites gas, and the fan limit thermostat rotates as it heats up. At the 100 degree tab the blower velocity seems to increase, at the 130-140 degree tab the blower velocity increases more, but the temperature seems to increase until the limit switch hits 200 degree tab and shuts it down. Then the cycle keeps repeating. The furnace never continues to run and cannot maintain the temperature that the thermostat is set to.

On my unit, all of the drainage hoses for the elimination of the condensation water are placed over blower motors or over critical circuitry. Leaky hoses have caused moisture to drip into the control boxes and corrode many connections. After cleaning the connections and replacing connectors, the unit still behaves the same. It is a very simple unit and has no error code LED.
Question: What could be the problem, what can I test further myself? How would you begin to troubleshoot this?

Thanks,
JCE

glennjanie 11-29-2008 04:43 PM

Welcome JohnCEberhart:
You mention 100* tab, 130-140* tab and a 200* tab. I wonder it these thermostats are the nickel-sized thermostats wired in series. If that is the case, you can get a new 200*, hook it up exactly the same as the old one and I think it will make the motor run on high speed. These thermostats are difficult to test because they are all wired together, but a click means it has kicked in and when the 200 kicks in it should kick out the other two.
Another possibility is that the three speed motor is burned out on the high speed. You can disconnect the motor and plug the wires into a receptacle, one speed at a time to see if it runs. The motor would typically have 4 or 5 wires to it, the green one being the mechanical ground, the white one the common, black for low, blue for medium, and red for high speed. Carefully plug the green wire into the half round hole in the receptacle, the white one into the longer plug hole and the colors, one at a time, into the shorter slot.
Please let us know you survived this test and how the situation works out for you.
Glenn

kok328 11-30-2008 10:41 AM

Instead of sticking bare wires into a 120VAC outlet with your fingers, how about we attach this motor to a three pronged cord and test it that way?
If you don't have an old appliance cord laying around, you can buy them at the big box stores for a couple of buck.

johnceberhardt 11-30-2008 02:17 PM

Hi Glenn and kok328,

No, unfortunately there is nothing in series that I’ve seen so far. The fan limit thermostat unit is a one-piece part that has a probe that extends into the firebox. There is a dial on it that rotates as it heats up. There are set tabs on it. The installer/consumer can set trip points on the dial. It is currently set so the lowest triggers or trips when it rotates to the 100 degree mark (the blower velocity increases), the second is set to 130-140 degrees (the blower velocity increases again), the last tab is the upper limit switch and is set to 200 degrees (the tab cannot be adjusted up, only down).

Since the firebox temperature seems to increase until the upper limit switch trips, I agree that it seems like the highest speed of the blower is either blown or not allowed to reach full speed for some other reason (hopefully a cheap relay, diode, or thermistor).

I’ll try the wires using an old appliance cord and not bare wires (thanks kok328). I should probably buy more life insurance anyway (keep my wife happy –ha-ha).
What kind of prices have you guys been seeing for the 3 speed blowers (motors)? I am seeing posts here and there that list them as running around a $1000 and no way to repair the control board even if the motor is still good. I am one of the few that used to make a living doing component level circuit board repair. If I can get a schematic, I can repair it.

John

johnceberhardt 12-02-2008 09:15 PM

Update
 
5 Attachment(s)
Still failing because I haven't worked on it yet. Heats a little and then resets. Here are some pictures.

Wires to blower are red-low (not connected), blue-med, black-hi, two browns and a white. Browns are connected to (through) what looks like a giant capacitor. Can't see the ground wire yet. I have the schematic so I can check voltages etc. More info soon as I find time to work on it.

Blue Jay 12-03-2008 10:24 AM

200 would be the upper limit and should shut down the burner, try changing the filter and or check the ducts for restriction.

johnceberhardt 12-03-2008 06:15 PM

Already did all that. It has a new filter and I removed the ducts to let it run wide open. The limit switch still slowly rotates until it hits the upper limit and shuts down (then repeats the cycle). The airflow is medium, it never goes to high speed. The airflow is probably not good enough to keep the temp from rising to shutdown. Is there a way to force the fan to hi with a jumper like on the old carrier weathermakers?

johnceberhardt 12-04-2008 10:02 AM

plug wiring
 
Quote:

Originally Posted by glennjanie (Post 25638)
Welcome JohnCEberhart:
You mention 100* tab, 130-140* tab and a 200* tab. I wonder it these thermostats are the nickel-sized thermostats wired in series. If that is the case, you can get a new 200*, hook it up exactly the same as the old one and I think it will make the motor run on high speed. These thermostats are difficult to test because they are all wired together, but a click means it has kicked in and when the 200 kicks in it should kick out the other two.
Another possibility is that the three speed motor is burned out on the high speed. You can disconnect the motor and plug the wires into a receptacle, one speed at a time to see if it runs. The motor would typically have 4 or 5 wires to it, the green one being the mechanical ground, the white one the common, black for low, blue for medium, and red for high speed. Carefully plug the green wire into the half round hole in the receptacle, the white one into the longer plug hole and the colors, one at a time, into the shorter slot.
Please let us know you survived this test and how the situation works out for you.
Glenn

I'll do this on Thursday or Friday. On my PSC motor the black is high speed and the red is low (according to the schematic and the red wire is currently not and has never been connected to anything).

glennjanie 12-04-2008 02:49 PM

Hey John:
I see the thermostat, not like I said at all but I understand how that one works too.
I see notes on the blower housing that mention time delays. The time delay is accomplished with relays, the two brown items in the lower part of that panel in your first picture. That's where I'm betting the trouble is. There are lots and lots of different kinds of relays so you will need the old one or complete information from the old one to buy a new one. Getting the wires hooked back the same way is also crucial; you might mark them with notes on masking tape attached to each wire.
If we know the purpose of the relay and understand the information on the relay, it can be tested fairly easy.
Glenn

johnceberhardt 12-04-2008 03:14 PM

Hi Glenn,

After I test the blower I'll check out the relays. Relays are usually cheaper than blowers so I hope that's where the problem it. When I first cracked the case open I found lots of leaky hoses dripping water into the control box (and on the relays). I squirted some WD40 on them but had to clean and replace a few spade connectors. The black high speed connector was in bad shape. There's a good possibility that they are stuck open.

Best regards,
John


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