Furnace/AC combo - no heat - no blower


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Old 11-26-08, 05:08 AM
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Furnace/AC combo - no heat - no blower

I have a International Comfort Products PGF024K060D combo unit. Here is the recent history:
My wife claimed it was working (on heat) several times in the past few weeks. I have not seen a problem, other than maybe a reluctance to turn on quickly. We live in SC, it's winter and very cold out (very = 30 by SC standards), the unit is outdoor on a concrete pad.

Here is the current status:
I awoke to find the lower half of the house cold (this furnace only controls on floor). Turning the fan on instead of auto did nothing. Changing thermostat batteries and swapping with the upstairs thermostat did nothing. I raised the temperature inside the house with our gas fireplace and turned on the AC. I heard it kick on, but the blower motor did not blow, and no air came out of the vents.

I have a little electronics background, but am a mechanical engineer, so bear with me. There is 220Vac at the furnace. The only switch it a little pull out plug that ios working properly. I found 220V prior to and after the contactor, which I now presume is for the AC compressor. I can activate this contactor manually and I get the same noise I get when I turn the AC on, so that's my best guess. I found 24V a few places as well. I cannot find a fuse on the circuit board inside the furnace. The only thing I see that looks odd is that there are two black boxes on board (presumably relays or contactors) that look like they might have gotten a little hot on one side. It doesn't look like anything catastrophic, but then again, I am an ME.

If anyone has idea, please respond and I will supplement quickly with more information and pictures.

Thanks in advance!
-Brian
 
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Old 11-26-08, 05:11 AM
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Also.. the unit as installed in 2002 and was new with the house. I haven't had a problem with it through the past two years we've lived here.
 
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Old 11-26-08, 07:20 AM
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Update: the control board has a charred mark on it under that relay. Now I am learning that I cannot course the part because everything but internet requires a contractors license. Any ideas?
-Brian
 
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Old 11-26-08, 02:02 PM
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check for blown fuses or circuit breakers. However, since you have char on a component, I would imagine you could damage something worse... unless its normal discoloration. Try and post a pic of it for those who are more familiar with heating/cooling
 
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Old 11-26-08, 03:37 PM
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Did you look for a fuse on the control board itself, in the furnace?
 
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Old 11-26-08, 03:43 PM
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I did not see any fuses on board, and I did look. I ordered another board for now. It is Honeywell ST910c 5005. Any ideas as to why the charring? I will post pics soon, but it is definitely a blown relay. What the cause was, I cannot say...

-Brian
 
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Old 11-26-08, 03:59 PM
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Old 11-26-08, 04:03 PM
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And here is the whole board from a vendor online
http://www.myhvacparts.com/Catalogue...%201084197.jpg

Once again, I cannot find any on board fuses, nor any in the cabinet. I see a contactor (presumably for the compressor) a transformer, a blower motor, a gas line, some tubing and ignition system, a gas valve, a rubber tube with some sort of diaphram and that's pretty much it in there.

-Brian
 
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Old 11-26-08, 04:04 PM
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If I was in your shoes, I think I would test various components first before putting in the new board.

I do not know what type of unit you have there. Does the furnace portion have an inducer motor? If so, I'd check that to make sure no dead short or that it was locked up. Same for a blower motor, just to name a couple things.
 
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Old 11-26-08, 04:20 PM
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I saw all 4 pics. I see dip switches. Make sure you read booklet and park all wires correctly and set dip switches according to instructions that match your unit, if necessary.

I was sitting here thinking if it could be at all possible the a/c portion could have caused this, rather than the heat portion. And about all I could think of is if say the contactor somehow shorted out and crosswired 120 line current to the 24 volt side and it came back to the board as 120 volts. Other than something like that, I'm thinking either simply a component on the board burned up for no reason other than age, or one of the other possibilities I listed.

Sure hate to see you blow out a brand new board, in the way people do with say a half dozen fuses, back to back to back.
 
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Old 11-26-08, 05:34 PM
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I hear you. I am familiar with DIP switches, and that's no problem. As far as the contactor, I am not absolutely sure how it is supposed to work, but I got a DC voltage off of one side (hard to tell how much - my meter is pretty garbagy) and an AC voltage (probably 220) off of the other. The only thing I know about the contactor is that I got the AC compressor to kick on both automatically and by depressing the contactor switch thing on the top. I assumed this combined with the voltage meant that I had a good contactor. If there could really be a problem, and it's likely, I could grab a good meter from work and check actual voltages, rather than just broad estimates if you think it's a possibility. I may try looking at the blower motor, but if I remember, there are several connections, and not just the obvious. I basically need a wiring diagram to know what to check. Maybe the rudimentary diagram on the inside of the door will do it - it's after 8 here and very dark, so not now. What voltage does the blower motor run off of? I could apply that voltage and see if it spins too.

Any other ideas?
-Brian
 
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Old 11-28-08, 04:32 PM
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Originally Posted by bowtie001
What voltage does the blower motor run off of? I could apply that voltage and see if it spins too.
120 AC.

You also mentioned in your post about checking something DC voltage. I think everything is AC, including the 24 volts.

There can be quite a number of wires to the motor. But 4 can be written off right away as - ground, neutral and 2 from a capacitor. That is 4 you can eliminate. The other color wires will likely be different rpm speed wires. They hook up one or 2 usually to the board. One color motor wire may be hooked to a heat terminal, and another wire to an A/C terminal. You may have another wire left over that may be on a spade connector called "Park", which is simply where they plug a speed wire that is not being used -hence the word "park".

You could have a bad capacitor. Do you hear the blower motor humming, if you are right there with the blower motor exposed, and the interlock door safety switch depressed? If it is, you could try to see if you could spin the blower wheel while it hums, to see if it goes. Make sure you spin it the right way, by spinning in the direction of the blower wheel's cupped vanes. Be careful of your fingers! If it goes, it is likely the capactor is bad and they cost only about $10 or so. A motor shop that sells these can test it.

If the motor makes no sound and all appears dead and you get 120 volts to the heat terminal on the board that leads to the motor, then you are going to have to test the motor. We can tell you how, but this is long enough for now. I need to see if you are still around, before spending more time.
 
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Old 11-28-08, 05:36 PM
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I am 90% sure the 24v was supposed to be DC. While the light was on (brought out the big light tongiht) I could see the fan ran off of 220 AC. At any rate, I plugged in the board earlier this evening, and everything seems to be working. The older board had a pretty big burn on the trace side. I am guessing something shorted it, it seems to have exposed traces, cheap board I guess.

-Brian
 
 

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