RUUD Silhouette II Furnace, No Heat

Hello,
I have a RUUD Silhouette II furnace that will not heat. The unit was installed new when the house was built in 1996. The furnace was working fine up until recently.

Model: UGPH-07EAUER
Serial Number: DF5D302F289604704
Thermostat/controller: Honeywell TH8000
Ignitor: Honeywell Glowfly Q3200U1004

It is pretty cold outside the house, ~25 degrees F.
The inside house temperature is slightly under 50 degrees F.
The thermostat heat setpoint is 55 degrees F, and the thermostat is set to heat.
The furnace filter is brand new (so no airflow restrictions from a dirty filter).
Power to the furnace is on.
If I remove the furnace top panel at the burner box and watch the start up sequence, the blower motor and inducer motor will power up (there is airflow at all open diffuser vents upstairs in the house).
The ignitor does not come on.
I do smell a very slight gas odor near the burners, so it appears that everything is ready to start the burners, but the ignitor doesn't come on.
If I remove the thermostat, and jumper the R and W terminals at the thermostat's wall plate, there is no change. The blower and inducer motors start up, but the ignitor still doesn't come on (so I guess that the thermostat is OK).
If I disconnect the ignitor's two leads and measure the resistance across the ignitor, it measures 46.1 Ohms. I am not sure what the resistance should be with a new Glowfly ignitor, but at least is does not measure open.
If I remove the access panel to the furnace's PC board and watch the start up sequence there, there are two green LEDs and one amber LED on the PC board. With the furnace bottom panel safety switch held down, the start up sequence shows the two green LEDs light up, but the amber LED does not light at all. I am waiting several minutes to watch this sequence, and still the same result. The blower and inducer motors power up, but no ignition.

Thank You for any suggestions you can provide,
GHamm

 

I suspect that your draft proving pressure switch is not operating to tell the logic board that there is indeed a draft through the furnace. This means the ignition sequence will not initiate.

Rarely is it the pressure switch itself but more often the connections to the draft fan that are the problem. Look for the rubber tube(s) on the pressure switch and check them for any splits or holes. If none, then check the nipples where the rubber tubes connect to make sure they are clear. You may need to take a succession of sizes of drill bits to clean out the nipples of any rust or corrosion.

 

Welcome to the forums.

You need to count the LED flashes and compare them to the chart on the back of the blower door. Since the draft inducer and the blower are both running.... you should expect to see an open limit switch code.

 

Thank you both for the leads. I will investigate and post back the results.

GHamm

 

On a RUUD (or a Rheem, they are the same company) the amber LED indicates the flame is properly sensed. One of the green LEDs is simply a power indicator and I forget what the other LED is for. It may be that there is no code for the draft proving switch, I know that is the case with my Lennox.

I know this about the Ruud/Rheem because my sister's furnace wouldn't do anything this last weekend. I jumpered the R and W terminals in the furnace and everything was fine. When I went in the house to look at the thermostat I immediately saw the problem. She had inadvertently touched the button switching from heat mode to cool mode. Once switched back to heat everything was fine.

 

Pete,
There are no flashing LEDs to indicate an error code when powering up the furnace. The two green LEDs light up, and the amber LED does NOT light at all. So the blower motor and inducer motor both power up, but the ignition sequence doesn't go any further than that. I have tried this several times, and the result is the same.

Furd,
I inspected the hose from the inducer motor case to the pressure switch. The hose is in good shape, no holes or splits. If I remove the hose, I can blow through it, so no restriction at the hose itself. If I attach the hose to the inducer motor hose nipple, and blow into it, there is no apparent restriction there.
If I attach the hose to the pressure switch nipple, I can hear the switch click if I suck on the hose, so the switch appears to be mechanically free anyway. Is there a better way to test this switch?

Thank You,
GHamm

 

Do you have a multi-meter?

 

Hi Furd,
Yes, I do have a voltmeter.

 

I'm just making this up as I go so I might be wrong. I am assuming that there are two terminals on the pressure switch although there may be more than one wire per terminal. Set the meter to AC volts and for a range that will safely allow for about 24 volts. Connect the meter across the switch, one meter lead to one switch terminal and the other meter lead to the other switch terminal.

You need the blower compartment door in place to hold the safety switch in. Energize the furnace circuit. The meter will either show zero or about 24 volts depending on whether the switch is normally open or normally closed. Different furnaces use different switches to determine if the switch is operating properly. A few seconds after the induced draft blower starts the switch should change state and that will be indicated on the meter with either a voltage or zero, the opposite of what was originally shown. If this is okay then the switch is okay.

Now maybe you don't get any voltage at all. If this is the case then check between the R and the C terminals on the thermostat connection strip. You should get about 24 to 30 volts here when the main circuit to the furnace is energized.

Post back.

 

FURD,
Examining the inducer motor plastic case, there are a few cracks visible. Is this cause for concern?

 

Here's another image, zoomed out slightly.

 

You want to do the electrical check descirbed earlier to see if the pressure switch is closing. Probably it's not.


The crack in the inducer motor housing COULD cause the pressure switch to fail to close. You can repair that by using a 1/4" nutdriver to remove the screws holding the inducer motor plastic housing to the furnace chassis, and pulling out the inducer motor assembly. Use some caulk to patch the cracks, and re install the inducer motor assembly.

 

I'd use a five-minute epoxy or maybe a high temperature silicone rather than caulk but otherwise I agree with SP.

Since I am making this up I'll leave you with SP as he used to do this kind of work for a living.

 

Ok, here's the update,
The pressure switch for this furnace is normally open, until negative pressure closes the switch. With the furnace wire leads disconnected from the pressure switch terminals, I measured the resistance across the these two terminals. It is open (infinite resistance), so the pressure switch does not have an internal short. Good.
I reconnected the furnace wire leads to the pressure switch, install the furnace box bottom panel (so the safety switch is down), and measure the voltage across the two pressure switch terminals (power to the furnace is on, and the thermostat set to heat). Voltage = 0, so something is wrong. If I remove the orange hose from the pressure switch, and start the furnace, I do not feel any suction at the hose (it is connected to the draft inducer motor case). The draft inducer motor spins, but there is seemingly no vacuum to close the switch.
At this point, I have to believe that the cracks in the draft inducer motor case are the most likely suspect. I looked online for a replacement OE draft inducer motor, and the new motor has a die-cast aluminum case. This is a good thing. By the way, Amazon has a great price on this motor.
Is there anything else for me to check? Unfortunately, I don't have a manometer, yet.

Thank you all for the excellent advice,
GHamm

 

>


Well, this is why I don;t like suggesting that tests on switches be done across the switch. The results above are ambiguous depending on a variety of things.

If you want to check to see if the pressure switch is closing, you can use either of two methods:

1. Set the meter to measure 24 VAC or more.

Connect one test lead to the furnace sheet metal chassis as a ground.

Use the other test lead to check the AC voltage on both sides of the switch.

When the inducer motor first turns on, one side of the switch will have 24 VAC to it, the other side zero VAC (the switch is OPEN).

When the inducer motor comes up to speed, you should measure 24 VAC on BOTH sides of the pressure switch (the switch is CLOSED)

If the switch closes when the inducer motor comes up to speed, the next step is for the hot surface ignitor to heat up.


2. OR: disconnect the wires to the pressure switch. Turn your multimeter to measure resistance and connect the test leads to both sides of the pressure switch. With the thermostat turned off, the resistance should be infinite (pressure switch OPEN). Leave the furnace wires to the pressure switch disconnected and turn up the thermostat to start the inducer motor.

When the inducer motor comes up to speed, you SHOULD see the resistance drop to zero (Pressure switch CLOSED)

If the resistance stays infinite, the pressure switch isn't closing ---usually for a reason.

 

SP, thank you for the detailed instructions on testing the pressure switch.

Test 1: This is a little puzzling. With the wires connected to the pressure switch terminals, I only get 0.12 VAC from either terminal to chassis ground after the draft inducer motor spins up. If I measure from terminal to terminal, the voltage = 0. I think the voltage was the same at startup.

Test 2: With wires disconnected, the pressure switch resistance goes from open before starting the furnace, to 0.4 Ohms after the draft inducer motor spins up.

Any idea why there is no voltage at the pressure switch?

Thank You,
GHamm

 

As I mentioned previously .... you have an open limit. Go to where the stat connections are on the control board. measure from R to C. You should have 24vac. Let us know.

 

Pete,
With power to the furnace and thermostat set to heat, I measure ~26.5 VAC at the R to C terminals.

Any idea why this furnace's control board didn't flash an error code to indicate limit failure?

I will test resistance across the limit's leads tomorrow and post the results.

Thank You,
GHamm

 

If there was an open limit switch... usually the inducer and blower run but there is no 24vac on the R terminal. I'm concerned that you aren't getting 24vac to the pressure switch.

I cannot locate the manual for this furnace. I need to see the wiring diagram to diagnose the missing voltage. You can take a picture and post it. It'll be on the back of the blower door. It needs to be as big as possible. Posting it on a picture hosting site and linking here would be great.

I don't know why you aren't getting any fault codes.... you should be.

 

The R terminal provides the low voltage that the thermostat can turn on to the W terminal to cause the furnace to turn on.


So you should have 24 VAC (or so) to the R terminal whenever the power is on, and 24 VAC should be switched on to the W terminal when the thermostat is calling for heat.

When the W terminal is energized, the inducer motor should start up ( as it is) and you should get 24 VAC at the pressure switch --- which you aren't.

Anyway, that's where to look for your problem --- why are you getting no voltage to the pressure switch?

I'd check the high temperature limit switch to see if that is closed (as it should be) or whether it might be stuck open.

 

Hello,
Resistance across the furnace limit switch terminals is 1.87 Ohms, with the wires disconnected. The limit switch is good.

I'll try to photograph the wiring schematic for the furnace tomorrow when it's light, and post it back here. If that doesn't work, maybe I can find one somewhere...

I agree with you both, finding the missing voltage should be the key to getting the furnace operational.

Anyway, thank you both for the effort.
GHamm

 

OK, here's the Wiring Diagram.

 

And here's the IFC Troubleshooting Guide:

 

Click on pictures for larger size.
Marginally better. You could shoot larger pics and resend them.

 

OK, hopefully this is a better image of the Wiring Diagram:

 

The DIY board has a pic limit of 600x600 and 50Kb file size. No matter how big you post it.... the board will compress it. That's why I hosted those two pics for you. They are at photobucket and linked here. If you can take a BIG picture of it.... like with a cell phone.... re-email it to me.

 

Hi Pete,
Let me try this again. Here's the Wiring Diagram from ImageShack:

http://imagizer.imageshack.us/v2/320...633/LLdlOx.jpg

Thank You,
GHamm