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Discussion Starter #1
I have an older (Think it's a 3100) unit that is not coming on. The first day it got warm enough to turn the AC on, I cranked it up and worked perect for 3 or 4 hours and then wouldn't kick back on any longer - I couldn't even get the fan itself to kick on.

I jumped the motor to see if it will still run, and it works fine. I then replaced the blower control circuit board. Still nothing!! Any ideas? I'm pretty much at a loss at this point, other than it being the thermostat itself. The thermostat isn't but a couple of year old digital variety, but I suppose it could be shot too. The display and everything seems to be working fine though. However, I could not jump across the thermostat wires to get the fan to kick on either.

Not getting any cooler here....anyone have a thought?
 

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I'm Your Huckleberry
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on the stat: pull the wires on the terminals g and r off. twist those together. if the fan comes on add the wire from the y terminal to call for cool, the condensing unit outside should come on. If you get cold air then your cooling works. If anything works while by passing the stat then your stat is bad.

Again, do not jump the wires, physically remove them and twist them together.

oh yeah, do all work with the the breaker to the furnace off as if you touch those stat wires to anything with power to them you can blow the fuse. turn the breaker back on after you have connected the wires.
 

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Discussion Starter #4
Wouldn't the circulating fan on the inside unit still come on in manual if it were the outside capacitor? I can't even get it to come on with the thermostat in manual on. That's what is throwing me.
 

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Discussion Starter #6
Ok, I twisted the wires together and turned it back on and NOTHING came on. Still no blower motor kicking on. :( Is that an indication of needing a new thermostat? I can't imagine what else would keep just the blower motor from kicking on when it will it I run straight current to it. Transformer? UGH!!

I would just call a repairman, but I lost my job a few months ago and unless the job fairly drops something on me SOON, I can only afford to do it myself or do without. If it was just me, I'd do without, but I have a wife and kids who are on me about getting it fixed....lol Sorry if it's a pain in the a55. The fan controller circuit board was $120 and I just can't afford a repair call. I REALLY do appreciate the help though...can't tell you how much.

on the stat: pull the wires on the terminals g and r off. twist those together. if the fan comes on add the wire from the y terminal to call for cool, the condensing unit outside should come on. If you get cold air then your cooling works. If anything works while by passing the stat then your stat is bad.

Again, do not jump the wires, physically remove them and twist them together.

oh yeah, do all work with the the breaker to the furnace off as if you touch those stat wires to anything with power to them you can blow the fuse. turn the breaker back on after you have connected the wires.
 

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No, it is an indication that you need to have someone come in and figure out why it is not working. Power still on to your apartment/house, breakers all on, panels back in place on the indoor unit, so that safeties are not tripped. If you have double checked all panels, breakers, switches, and still nothing, call a HVAC tech.
 

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I'm Your Huckleberry
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Ok, I twisted the wires together and turned it back on and NOTHING came on. Still no blower motor kicking on. :( Is that an indication of needing a new thermostat? I can't imagine what else would keep just the blower motor from kicking on when it will it I run straight current to it. Transformer? UGH!!

I would just call a repairman, but I lost my job a few months ago and unless the job fairly drops something on me SOON, I can only afford to do it myself or do without. If it was just me, I'd do without, but I have a wife and kids who are on me about getting it fixed....lol Sorry if it's a pain in the a55. The fan controller circuit board was $120 and I just can't afford a repair call. I REALLY do appreciate the help though...can't tell you how much.

Your furnace control board should have an LED light which will give you a flash code. You should have a legend on the inside of the service panel of the furnace which explains what that flash code means, granted if you do not have power to the furnace your control board will not have power to give you a flash code. The furnace door switch needs to be pushed in as well or you will not be giving the board power and again, no code will be present.
 

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Discussion Starter #9
Although my testers are indicating that there IS indeed power going through the new fan control circuit board, the status light will not do anything (I have the door safety switch pushed in as well). I'm show power through the control board, to the transformer and the fan will run if I remove the wire from the board and jump it across the power coming into the board. The is no power going to the fan wire when it is plugged into the board, however.

Crossing the r and g wire had no effect at all on anything.

Long hot day trying to figure it out and it's after 2am now.....I'll sleep on it and maybe be able to see something in the new day that I'm not now. Last year I'd had a couple of occasions to where it just quit working and I'd flip the door safety switch a couple of times and it would start up again fine. I jumped across the wires of the safety switch and it had no effect BTW. Here's a thing though, I just though of.....Last time I did had to have the door off, something made a clicking sound when the safety switch was pressed in - that's not there now. Is there a relay that I'm not seeing that could be at fault? Grasping for straws here I guess.

Doc, I REALLY appreciate the help on this that you've given....BIG TIME! I KNOW it's some small something that I'm overlooking. I was so sure that it was the controller board that it threw me when the new one did nothing. I used to work part-time with an installer years ago, but my memory isn't what it never was.....lol
 

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Post the complete model and serial # and pics of it with the 2 doors off and maybe we can recognize it and help more.
 

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Discussion Starter #11
Here's what I could take with my phone...hope they are clear enough. One is of the complete ID label

https://picasaweb.google.com/lh/photo/-Zywca6VqDg26LYwt0NrGA?feat=directlink

https://picasaweb.google.com/lh/photo/pzGBVDi27B68M88FE608Ag?feat=directlink

https://picasaweb.google.com/lh/photo/RXs2-WhZqlvgGSrNKpHolg?feat=directlink

Old controller board that I replaced.....

https://picasaweb.google.com/lh/photo/AfZjPCDBLrKiOxcSoUQYog?feat=directlink

Looks like transformer was replaced (and the old one left on) before I bought the house 5 yrs ago. Hope this helps.
 

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I'm Your Huckleberry
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at this point it is either the blower motor itself or the run cap or both. if you have mfd capability on your meter you can test it. I'd say you can test it by amp draw but if your motor isn't spinning than no amps are being drawn so that leaves a new control board that is sending voltage to the motor but the motor is not spinning.

Run caps start the motors and are notorious for going out yet they are cheap, less than $10. The run capacitor is the silver can looking thing with the wires on the bottom (so the capacitor is upside down) in the pic, just to the right of the control board and speaking of the control board, it should be mounted solid and not left hanging or you will have problems.

There will be numbers on that cap, something like 5 uf or 6 uf or 7.5 or 10 uf or whatever it may be plus the +/- percentage number and the voltage. Match all of those numbers from the old cap to the new capacitor EXACTLY.

Try that first and if still nothing than it's most likely the fan motor itself. if you get a new replacemnet motor than than you will need to get the exact match capacitor for the new motor.

Capacitors holds (stores) voltage and spikes current to shift the electrical phase, causing it to spin so turn all power off to the furnace before sticking your hands in there or you will get elecricuted.
 

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Which blower control board did you use to replace the original. Those universal boards don't always replace the OEM ones properly and I avoid using them. It also needs to be securely mounted and grounded properly. Furnace needs to be grounded properly too. Poor grounding can damage circuit boards. Looks pretty rusty to me and not in good shape. New board may now be damaged. Hate saying it but throwing parts into it without knowing the problem may cost more than a Pro to do the job. I would consider a new furnace as that one is 10 yrs old, needs expensive repairs and the heat exchanger may be in fair to poor shape and not last too much longer. Average life of the exhaust fan/ventor fan is 10 yrs.
 

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Discussion Starter #16
Sorry, Doc, I always seem to get the two ass backwards and shouldn't, but then I can't remember my name half the time...lol

Capacitor hasn't been changed that I can tell. I'm also NOT getting any current flow through it with the power on.
 

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Sorry, Doc, I always seem to get the two ass backwards and shouldn't, but then I can't remember my name half the time...lol

Capacitor hasn't been changed that I can tell. I'm also NOT getting any current flow through it with the power on.

Not getting any power through the control board or through the run cap? . If you are receiving voltage to the fan motor and it is not spinning than it is the cap or the motor or both.
 

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Discussion Starter #19
The blower motor runs fine.....I can disconnect the lead from the board and jump it across the power in and it starts right up and runs great. I'll have to wait till Tuesday to get a new capacitor as there is nothing open for the next two days here.

As for the controller board, the HVAC parts place here says that the replacement would match up to the old board. New board is a Honeywell ST9120U 1011 and the old board was a Honeywell ST9120C 4057. It is listed as a match on the box the new one came in.


at this point it is either the blower motor itself or the run cap or both. if you have mfd capability on your meter you can test it. I'd say you can test it by amp draw but if your motor isn't spinning than no amps are being drawn so that leaves a new control board that is sending voltage to the motor but the motor is not spinning.
 
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