Amana Heater Mod GUO090X50A

[winenotwhine]

This is a Heat command 90 that was working fine until my 3 year old put a comforter over the upstairs intake. I didn't notice this until hours later, probably because the unit kept on producing heat.

Shortly after I pulled the comforter off, the heater stopped heating  though the blower keeps sending cool air through the ducts. When I checked it out, the bottom peep hole was blinking slowly but continously. I changed the filter, checked for any loose wires (none found) and put it back together--it blinked three times right at start up, then nothing.

Blower comes on, there's a click at the fuel valve but no flame.

[hvacdrd]

Is this an upflow or downflow unit? Also pull the cover where the blinking light is and see if there is a diagnostic chart that tells you what the blinks mean. It is usually printed on the panel you remove for access or on the control itself.

[winenotwhine]

I assume it's an upflow unit since the heater is located in the basement and delivers air to the two floors above--the return air vent is on the second floor.

The diagnostic chart says three blinks means the pressure switch is stuck open.

[winenotwhine]

Correction-Model # is GUD090X50A, not GUO.. as originally posted.

[hvacdrd]

OK, the pressure switch has nothing to do with the blanket over the return air, just a coincidence.

On power up with a call for heat, the exhaust motor should start first.

Check the pressure switch tubing for obstructions

Verify that the condensate lines are clear

Check the exhaust pipe for obstructions

If those check out ok then you will need to test the pressure(negative pressure) at the switch to move further.

If you are not sure what I am talking about let me know and I will try to explain it another way.

 

[winenotwhine]

I'll need some help defining what's what.

First, is the exhaust fan separate from the blower that pushes the air through the ducts or does the blower perform both functions, i.e. distribute heated air and exhaust air with condensation?

On power up, the main blower comes on immediately. So if there's a separate exhaust fan, I'll have to check this. I know what and where the exhaust pipe is---I'll check it.

Not sure where to find the condensate lines.

Is the pressure switch a gas pressure switch---the squarish metal piece near where the gas supply enters? If so, the tubing is the gas tubing?

Tks.

[hvacdrd]

OK, you get the picture of the day.... Another thing to check would be the air intake pipe. Both the exhaust and intake pipes are the pvc piping that runs from the furnace to the outside. Most Amana's in our area are the GUC model that are single pipe - meaning only the exhaust is ran outside. So first try removing the intake pipe from the burner box, just enough to separate the pipe from the box allowing 1" or so space. If the furnace fires up from there, Jr. may have filled the pipe from the outside this summer, then it is a matter of clearing the pipe. Look these pictures over and we will go from there.

Amanafurn.bmp

[Samurai Appliance Repair Man]

Dayyam! That's the picture of the Month! Nice job, hvacdrd! Where'd you get the base picture to work from

[winenotwhine]

OK--starting with your initial reply...

The exhaust motor starts up immediately though rather than first, it's simultaneous with the main blower or a split second behind.

All the pressure switch tubing looks good, no kinks or obstructions.

I disconected the condensate lines as they leave the unit with no change at start up.

I checked the exaust pipe outside--it's coming out nice and steady and sounds just like it always does when I've ben near it in the past. Both the intake and exhaust pipes (2"pvc) run outside--both have a beefy screen to prevent tennis balls and whatever from being crammed inside.

I did also remove the air intake above the burner box--no change.

So I guess it's on to the pressure test?...

[winenotwhine]

Don't know if you saw my last post--I'm wondering what the negative pressure test at the switch is all about.

Thanks

[hvacdrd]

See if you can make sense of this. Not sure why it came out so fuzzy when I attatched it. Do a quick electrical test at the pressure switch before we go further. Test from C to NO - reading should be zero v-ac. If it is 24v-ac then this confirms we have a switch problem and we will proceed. For your model the switch contacts open/close at -1.20" w.c. (translation - "w.c. = inches of water column (28"w.c. = 1 psi).

[winenotwhine]

Voltage across C and NO is 24 ac for the first four seconds when the unit fires up. It then drops to zero and doesn't move. There's a click at about 15 seconds after start-up--the ignitor.

Only confusing thing is that soon after I hear the click I smell gas. Gas, click but no fire. Could we have a dead ignitor?

Back to the pressuer switch, I made the assumption that the voltage test was a test to be done  indepenantly. That is, without reference to a manometer reading. If I'm wrong, let me know--I'll re-run referencing pressure readings.

Thanks--alot, the image came across with no fuzz--easy to interpret.

[hvacdrd]

If pressure switch contacts are going from 24VAC to 0VAC then the switch is closing. I'm a little confused though. I thought we had a fault code '3' meaning pressure switch failed to close.

Am I reading correctly that the ignitor is glowing? Gas valve opens but does not ignite? Normal sequence is 1-combustion blower starts, 2-pressure switch closes, 3-ignitor warm up 17 seconds (50A55 Control),4- trial for ignition 3-5 seconds, 5-burner lights. Where are we in this sequence? Do you have a glowing ignitor when you hear the gas valve click?

It would be OK to remove the burner access cover to observe the burners during startup.

Ignitor resistance at 70-75F should be 50-400 ohms (usually around 100) - Amp draw is 4-5

[winenotwhine]

Her's the sequence---On start up, I get the three red blinks (only once--it doesn't repeat). Both fan blowers come on. Then at about 15 seconds I hear a click that I assume is the ignitor. Yesterday when I went through this start up multiple times I then smelled propane-(also smelled propane at the same time otside while checking  the 2" pvc exhaust pipe). Tonight I don't smell the propane .

Either way, I've looked each time and never seen any glow in the combustion chamber. I removed the cover plate at the burner box. There's a couple of red wires entering from above that connect to a white modue from which 4 one inch prongs descend into the combustion box. I went through start-up--no glow, no overall change at all.

The descending prongs looked rusty and frail so I poked gently with my screwdriver--the two middle portions fell off so I assume we have at least one part in need of replacement.

[AccApp]

Sounds like the ignitor was electrically open and you finished the job by poking it. Take it out and get a replacement. It should definitely be glowing before the gas valve opens.

[hvacdrd]

Definitely need an ignitor, not sure what I lost in the translation from the get go. The ignitor is fragile so handle with care. Here is the ignitor you need.  Amana part number 10041601, Robertshaw 41-401, White-Rodgers 767A-369

 

[winenotwhine]

The ignitor did the trick--fired right up.

However, the red light still blinks three times on start-up. That's why we didn't go first to the ignitor---the control module says a three blink signal means the pressure switch is open.

Thanks for all the help.

[hvacdrd]

Well it was fun leading you astray. I can't believe I got so carried away on an Amana. Almost every no heat call I run on these is either a bad ignitor or poor flame signal.

The ignition control must pick up on the open pressure switch before the inducer motor has time to get up to speed. Usually the controls will allow some time before displaying a code.

 Thanks for the update.