Residential HVAC guys (or anybody else for that matter), need a professional opinion.

[cowpuc]

Tippy wakes me up and says she smells something hot in the house.. Couple minutes of searching and I find that its coming from the heat vents. I go downstairs and discover that the squirrel cage blower that forces warm air thru the vents is not running. The vent pump that brings in fresh air for the burner and the burner are still functioning.. There is small led on the gas control valve that is signaling NO codes.

Some diagnosing revealed what appeared to be a questionable Start Capacitor for the blower motor. It did test functional but weak on a cap test to me.. I shot into a HVAC joint in town, a tech there tested my cap and said it tested weak to him to. He did not have an exact replacement but had one that looked like it would work. The new one tested within specs where mine did not. 1st question: Look at pics of both caps. The grey one is the old one, the silver one is the new. Does the silver look ok to use in your opinion..

After replacing the cap the blower would still not function. I jumpered the blower motor leads and all seven of them spun the motor right up.. I had gotten no codes indicating a fault on any limit switches but went a head and tested em anyway, all looked good. All the low volt stuff on the board tested fine. I noticed a small dark spot on the board itself, popped it off its mount and immediately found a burned pin. The pin was the first component on the boards connector attached to "L1" (110v supply for the board). The neutral connector looked fine. I cleaned up the back of the board and resoldered the pin. Put it all back together and she seems to be working fine.

All that explained, got a few questions:

1. Is it possible that the weak Start Cap caused the L1 connector on the board to get warm enough to loose its connection.

2. The board number is - Furnace Control Board ST9160B 1050, the furnace is an Air Quest High Efficency that is about 12 years old. Take a peek at the pic's, any idea if this failure is common, any recall on this board, should I replace it even though it is now functioning fine on my resolder job?

3. I am thinking that the hot odor we smelled was probably dust that had gathered in the heat exchanger area. Since the blower that forces air around the exchanger is the one that died I am thinking the heat exchanger got hot and the "dust" on top of it started smoking (it smelled that way). Is it possible for this incident to have done enough damage to the heat exchanger that it would leak? If you were repairing this unit, would you normally check the exchanger and if so, how?

 

Thanks in advance to any and all responders!!

 

Puc

[Wrench]

The new gray capacitor is a replacement for your old one, the microfarad rating is the same. That's what the 10uF on it means. New capacitors are not oil filled like the silver metal one you have thanks to the EPA. As far as the board goes, if soldering the burnt spot fixes it then you are that much ahead. It is possible that the motor was drawing more amps on start due to the capacitor being weak and burnt that spot.

[Barry.B]

hi Cowpuc here in Canada we are not aloud to repair the boards after they have burnt like that . what i remember they are not to expensive and do you want to take a chance on the house burning down with you or your wife in it . And get the right capacitor for it to .For the heat exchanger do you have a way to inspect it and how long was it running without the blower on

 

Barry

[uncledj]

You should be good to go. Microfarad rating of the two capacitors is the same, voltage is higher. When it comes to capacitors, you can go up on the voltage, but not down. (370v and 440v are the two most common voltages). As far as the microfarad rating, they say + or- 10%, always go a bit higher rather than lower if there's a discrepancy. A weak capacitor can increase amp draw, but I doubt it'd be enough to fry a healthy solder connection. The more common issue is a failing / failed mini-relay on the board.

My opinion is that the board had a poor solder joint, which you so capably corrected. You may want to give the blower wheel a bit of a jiggle to see if the motor bearings are ok. A bit of end play is ok, but ANY side to side play indicates a failing blower motor. Failing bearings typically increase amp draw. When this is happening, you can usually hear a bit of a "struggling" sound when the motor first starts.

As far as the smell, I'm sure it was an overheated heat exchanger. I highly doubt that it caused any damage to said heat exchanger. If the exchanger ever does fail, it'll be VERY evident in the efficiency of the flame.

The only thing that has me a bit befuddled is why there's no limit trip indicated....unless the furnace had cooled, and the limit reset before you were looking for the fault code. Depends on how the board is set up. Some store all codes, some will allow the code to go away once the issue is reset.

I think you're OK. If you were a customer, I'd have replaced the board, but if it were for myself, I'd have done the same thing you did.

 

I don't do much residential work any more....I spend most of my time on the roofs of malls and plazas, but the principals are the same.

 

I think you can take pride in a problem confronted and resolved.

 

27+ yrs HVAC Tech.

[Flyinfool]

Ok, I am a professional, just not in residential furnaces.

A furnace is simply the opposite of a snow machine so that gives me some unique experience and insight.

 

As for the heat exchanger. Do you have a carbon monoxide detector in the house? If not you should. I have 3.

 

There should be a limit switch in there for plenum temp, once it got to the set temp the burner shuts off. This should have kept the heat exchanger from getting to hot. In normal operation this switch should never trip, it is there for your exact situation, lack of airflow over the heat exchanger causing overheat.

 

I would look at the PC board close for any more poor solder joints, maybe give all of the connector joints a touch with the iron just like we often have to do on our bikes. Also if visible, take a look at the relay contacts.

Edited March 25, 2015 by Flyinfool

[Brenner]

Puc, I am experienced in alternative fuel for vehicles but not an installer or HVAC repair expert but one thing I do know and that is in my area if a board burns like your shown it is to be replaced and not repaired. Also in my area if a board in a furnace has been submersed due to flooding even if it still works fine it is recommended to replace. I am a landlord and am liable if my tenants are harmed or lose their belongings due to not following these recommendations. I personally have installed 3 furnaces and passed all inspections. I do know that if your heat exchanger was heated and did manage to crack the danger would be carbon monoxide poisoning. When furnaces are older it is one of the items that are inspected in my area. If it was me I would be looking for a new board and run the new capacitor. Even though the damage was in the fan control circuit the newer hot surface ignition or spark ignition controls are best not chanced for the few dollars that they cost. Your call, you will not always be there to keep an eye on it.

[cowpuc]

SHE IS RUNNING SUPER GANG!! Cycled thru a bunch more on and off's, some from me playing with the thermostat and two on its own in maintaining heat - PERFECT with no failures!!

 

A HUGE thank you to all of you for your thoughts and idea's on this little opportunity to learn - ALL of your input is greatly appreciated!!

Hey Unc, THANKS FOR THE COMPLIMENT ON THE WORK:happy34:!! Its always been the old "cant win em all - BUT YOU CAN TRY" routine with me!!

 

I did stick an amp probe on the blower motor, amp draw is spot on! The Squirrel Cage rolls freely like its on ceramic bearings, no funny noises or bearing play. No out of balancing. The "veins" in the squirrel cage were all nice and clean, no build up like the filter was not doing its job (gets a new one every month). The furnace sets high and dry, we have had flooding in the basement twice now since we moved in (house was built in 02) but the water never reached the furnace itself - installed 2 sumps last year - worked perfect! Burner flame is real pretty light blue with no yellow happening..

I tried carbon monoxide testers back in the 90's at our old house and found them to be wayyyy to sensitive, constant false alarms and have never revisited that nightmare. I really appreciate the idea though Fool and would be happy to give it another shot. Any idea if they have improved? Any suggestions for good ones that dont do the false alarm routines?

About the repaired Circuit Board, I take what you guys are saying about "REPLACE IT" very seriously and am going to go forward with doing exactly that. That is VERY uncommon for me cause I really am a do it myself kinda guy BUT,, your points are well taken!! It got to late in the day today because of that "I CAN FIX IT MYSELF" side of meand I ran the clock out of time to be able to search locally for a new board here. I did jump on ebay and amazon real quick and noticed right away that the ONLY exact replacements for my board are USED - only available new are an "up graded" version made by Honey Well.. Normally I have NO problem using "salvaged" parts (I do that, A LOT ) BUT again, I get the point about the safety involved here and really APPRECIATE the concern - I am gonna replace this one with a new "up graded" version.. (Furnace just cycled off again)

 

I will shop around here locally tomorrow and see what kind of $$'s I can grab one for, if they are close to Ebay prices I will grab one and stick her in tomorrow. If not I will keep a close eye on this one and survive for a few days while waiting for the snail mail!! Maybe even rip the old one back out and see if I can get my grubby little fingers inside that relay switch that was mentioned just for the fun of it!!

 

THANKS AGAIN FOR THE INPUT GANG!!

Puc

[billmac]

I had a board go out and they changed it out, $385.00 for board, house call and changing out. telling some people about it and one guy said they change the board because of warranty and they will fix the board and use it on side jobs that get no warranty. So if you have a friend that has a friend that can fix it for cheap that 's usually the kind of board they use. You did good.

[MiCarl]

'puc, I did a similar repair on one of my furnaces 8 or 10 years ago (not the same one I had trouble with a month ago). Been working fine ever since.

[BigLenny]

Puc,

 

I am not an HVAC expert and I do not have an ounce of advice I can give you on this one. But, I just wanted to tell ya; I greatly enjoy your natural sense of adventure with all the bike travelling stories you tell, and when I was reading this thread and I could feel your natural urge compelling you to fix this sucker by yourself because after all, you truly are a jack of all trades, it finally hit me like a brick in the head............WHEN I GROW UP, I WANNA BE COWPUC.

[ricksbike]

I don`t know a thing about Home HVAC--but that sure is a lot of wires for an old codger to be dealin` with--LOL.