Amana Air Command 80 Gas Fired Furnace (4 blinks) troubleshooting

Yes, you may ask.

The next step, at least for me. Is to check to see if the furnace is really over heating. I've seen a bad high limit switch. In that case, the furance kept shutting down, but the furnace and the ducts never really did get hot.

So, I'd want someone (maybe the tech, maybe yourself) to see if the duct gets very hot, where the duct comes out of the furnace. If dirty evaporator is the problem, then the top of the furnace will likely be too hot to touch. Most of the high limit switches I've worked on, run about 180 to 200 when they trip off. And that's too hot to put your hand on.

Please go to the furnace and (very carefully) try to touch the grey metal on top of the furnace, where the heat goes to the house. Is it burny hot, luke warm, or room temp? That will tell us a lot. Also feel the top inch or so of the furnace, where it meets with the ducts. Is that burny hot, luke warm, or room temp?

Still curious if the ducts up top of the furnace are hot. I'll insert some American language translation.

Describing the problem--the High Limit is being triggered; I believe that's the high pressure sensor you mentioned earlier. That means the fan is trying to blow air, but it's backing up. Another possibility is the motor overheating and triggering it's thermal protection switch, which will reset when the motor cools orr.

CY: More likely a temperature sensor near the top of the furnace.

The motor isn't over heating, so it and the High Limit are working correctly, and the problem is that something is obstructing air flow downstream from the blower--like a coil full of lint and debris, which got that way due to the filter not being changed monthly like it's supposed to be.

What it cost to get the same basic answer your got from the first tech; the coil needs to be cleaned. Have whichever outfit will charge less do it.

CY: Cheaper isn't necessarly gooder, the cheap company may use sloppy labor.

Yes, you may.

Does anyone know which one it is?

Who knows?

It's a type of motor.

My guess is that it is the smaller motor that has the smaller starting torque needs.

Doesn't seem like anyone here is doing anything but enjoying your misery.

Jeff

I'm not a HVAC repairman, so take what I say with a grain of salt.

The ventilation motor, the one that blows the hot air, tend to be multiple speed devices. There's usually jumpers somewhere to set that. It sounds like he reset a jumper to a higher speed.

The fact the motor is not hot leads to the motor not being bad. If it runs and doesn't overheat it's probably OK.

You got a problem using google?

Here is the result for high limit kicking out:

Shut it down and clean it out. You've gone this far. Don't let those wimps stop you. Just make sure you put it back together right!

Jeff

Yep; I know.

Exactly what we all love about christians.

Jeff

Convert; then you'll know, also.

Donna, They are speaking of the blower motor (larger one) that supplys air to the registers in your home. The smaller combustion air blower may also be a PSC motor. By the way, whatever you do, do NOT take Stormy's advice. He has proven time and time again his pure ignorance of almost everything. Bubba

Sorry, it goes against my beliefs of being nice to others.

Jeff

I read about the PSC permanent split capacitor that was kindly referenced prior.

I see a large pack-of-chewing-gum sized thing, covered in dust, on that larger motor, which, when cleaned, had electrical terminals. I'm supposing this is the PSC motor's capacitor. So, I will assume as you suggested it's the larger motor.

Tomorrow is the cleaning scheduled, so, we'll see if that does anything. He said he might have to cut holes in the ductwork so we'll see if that changes things a bit.

I don't know what else to do at this point. Donna

OK. That makes sense. I see a LOT of wires in there. Maybe he moved some around. I should have taken a before/after photo. I did this time so when he comes tomorrow I'll have something to show beforehand and after it gets cleaned.

I never knew this cleaning stuff was so important.

BTW, how much do cleanings cost for most of you? $400?

And, how often do you do them?

He will be here from 10am to 1Pm he said, so, it can't take longer than 3 hours.

Is this reasonable by normal standards?

Donna

If it is the evaporator coil that needs cleaning, it might be a heck of a lot of work. Depending how the unit is piped in, and how the sheet metal is worked. Might need to take the freon out of the AC, and take the coil out from over the furnace. That could be several hours work.

Actually, if you have a good filtering system you most likely should NEVER have to clean that evaporator coil. Yes, it's relatively expensive to have to clean an evaporator coil that is hidden in a plenum with no access. If the refrigerant lines have to be cut to remove the coil the price goes even higher. When finished, hopefully the tech will put in a "split door" so you can access the coil a lot easier the next time. When finished, the temp rise through the furnace will need to be rechecked as more airflow through system will lower your temp rise causing cooler air coming out the registers. Bubba

Hi Bubba, Thanks for all the advice. It's done. It works. He charged $400 and cleaned the coils and it works. I asked about the fan speed and he said he left it at the higher speed and that it wouldn't hurt the system.

I understood all that you wrote except "the temp rise through the furnace" part. What is the "temp rise"?

Thanks, Donna

On Wed, 30 Jan 2008 05:53:50 -0700, Donna Ohl, Grady Volunteer Coordinator wrote: I learned a lot but I still would like to know if I can ask some questions.

I posted a picture of the "evaporator coil" before cleaning here:

QUESTION 2: (see picture 2) I don't see how I can get to the bacterial pad he put near the coil. Are they supposed to last forever? I don't see how they can but I don't see how I can replace it myself. Did I miss something?

QUESTION 3: (see picture 3) Does that evaporator coil cleaner actually work more than a short while? Bacteria can gro back real soon, so I was wondering if that disinfectant actually works over the long term.If not, where do I spray it now that I have a full can of it?

Thanks for your help, Donna