I have an old Bryant furnace here that's mostly very reliable. It's a model 394GAW036100
She'll make heat when called for but even after a good long while fan will not come on. A bunch of years back fan wouldn't turn OFF so I replaced PC board which solved that problem. I recently changed PC board AGAIN but fan still will not come on.
Winter's coming ; ) I'd sincerely appreciate some guidance.
That's an older Carrier/Bryant board.....HH84AA011
That would mean your furnace is around 30 years old.
Furnaces don't live forever. Be sure to have the heat exchanger checked for rust thru.
The heat blower is directly controlled via a timer on the board.
It should be 75 seconds on and 105 seconds off.
G is the abbreviation for blower.
That has Gc for cooling blower speed and Gh for heating blower speed.
Black blower wire for high speed cooling is on HI terminal.
Red blower wire for low/medium speed heating is on LO terminal.
White blower wire is on COM.
Try a jumper from R to Gc. The relay should click and the blower will start on high.
Last edited by PJmax; 09-06-22 at 10:08 AM.
Reason: correction
This is great and thanks for clearing up heat and cool speeds.
So to be clear "R" is the red wire attached to LO terminal?
I'm jumping this red wire to terminal Gc and Gh to see if fan runs?
iow jumping LO to Gc and Gh?
There's no point of doing any troubleshooting without first pulling the blower assembly and visually inspecting the heat exchanger for cracks, holes and rust.
The probability that this furnace is still safe to run is very low unless you're in the south and it has barely run.
Even if hxt still okay, if your area gets real winters you should get a new furnace over repairing yours, as yours is only 60 to 70% efficient. The ignition control system is also obsolete and parts are not commonly available.
Jumpering from R to gc would test the motor in continuous mode.
We're in MA, I understand that a new furnace is a must and I will begin investigating by reaching out to Mass Save. We just finished an 8 month to-the-studs renovation of our 2nd floor apartment and we're <really> not in a good spot to get a new furnace, I'd like to try to get through this winter if at all possible.
Based on what you wrote I take it blower has to come out to get a look at HXR?
As far as blower goes I'll jump R to Gc and Gh tomorrow.
- If blower runs?
- If I get nothing?
I do have a multimeter btw.
Thanks again I do you appreciate y'alls expertise,
Mike
If the fan runs, it means the tap used for cooling and continuous fan works.
Would need to go in with a meter and see if in heating mode, it is energizing the heating fan terminal 75 seconds after the burners light.
If it isn't, need to see if power is present on Gas-3 terminal on the board when the main burner is on - if you have power there and fan isn't timing on, board is defective.
I can get more specific later.
The heat exchanger can be partially inspected from the burner inlets, but to get a good view of all of it, need to inspect from the top or bottom -> so blower removed or access hole cut into plenum above, if there's no a/c coil directly on top of the furnace.
If the heat exchanger is compromised, you must replace the furnace before winter.
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When replacing the furnace, if windows have been changed and or insulation added, should downsize it.
Even if not, many furnaces are over-sized.
Ok .. main burner's on and I let it run awhile: when I jump R and Gc, relay clicks but fan doesn't come on.
When main burner has just lit V at Gas 3 is zero. When burner has been running for awhile V reads 60 mv which is weird right?
How much voltage should be present at Gas 3?
Thanks,
Mike
Last edited by TheGuitarFairy; 09-05-22 at 02:01 PM.
Did you check with that wire connected, or disconnected?
Would need to be connected, or check wire itself, not board with it disconnected.
Did you set your meter to AC volts? That's where it needs to be, not dc.
One meter lead needs to be on common to complete the circuit.
Now, based on the fact cooling relay clicks but fan doesn't come on though, should jump right to seeing if board is applying to heating terminal.
After 75 seconds of burner on time, check for line voltage (120v ac +/-) between Lo and Common on board.
If there's power, you have a bad motor -> the motor in your furnace doesn't use a capacitor.
If there isn't, need to check for power again at gas-3.
BTW without fan running in heating mode, high limit should trip and shut off burners.
Please do not ignore advice to check heat exchanger - if it's bad, you can not run it another season, the furnace must be replaced before fall.
My meter is digital
I can't find a capacitor, I don't think there is one.
Motor spins freely by hand, no resistance
- With burners running I checked V between C screw terminal and Gas 3 w/ wire still attached to board and was getting that reading in the mv's.
- Also checked V between C and <G3 wire> w wire off G3 and got same mv reading.
- After burner was running 75 second I checked V between Lo (terminal on board) and C terminal and also got a V in the mv's
- W/o fan running high limit did turn off burners eventually.
Thanks you, Fellas,
Mike
edit PS .. put a call in to HVAC tradesman, waiting to hear back. Just 'cause it's my nature I would like to figure this blower thing out ; )
- thank you again for the help and sharing your knowledge like this.
Last edited by TheGuitarFairy; 09-06-22 at 05:39 AM.
In a previous thread several people recommended calculating the load when looking at new furnaces.
The house involved is 1 1/2 stories with a finished basement. The supply ducts have no dampers. In the winter (sometimes down to 25 below F), electric baseboard heating in the basement does a good job keeping those rooms warm as needed. The gas forced air furnace warms the main and upper floors adequately in the winter, but my thinking is that manual dampers in the ducts would be nice.
In the warm months, the basement is always cool, never needs AC. So much cold air gets down there through gravity and registers (even if fully closed) that it is too cold whenever the AC is on. The main floor can be kept comfortable by the AC, but when quite warm the 2d floor requires so much cooling that the main floor is overly cool and the basement frigid.
When calculating load, shouldn't you take into account that the basement needs no heat or AC from the furnace and coil?
Also, do you need more tonnage to push more AC to the 2d floor, or can you accomplish that with dampers or motor HP? When looking at new furnaces, what feature would you focus on to get enough heat to the 2d floor? The ductwork lacks dampers and the supply registers are in the floor and returns in the upper walls; I expect these issues affect efficiency quite a bit. All of the room registers can be opened and closed, but wouldn't in-duct dampers help?
P.S. Are there tricks to adding manual dampers, so that it could be done DIY? All the basement ducts (rectangular and round) are reachable.
Thx.
Hello all -
I am considering purchasing a home currently heated by forced hot air via oil. I have confirmed gas is available in the street. The house I currently live in, has forced hot water (originally via oil) and I had the boiler converted to burn natural gas instead, since gas was available in the street and the gas co did the line installation for free if I hooked up my heat to it. My question, is whether a conversion burner gun can be put on a furnace, the same way it could be for a boiler. The oil furnace is on the newer side, so don't think it makes sense to walk away from it, but if I could get natural gas into the house now that would be awesome.
09-03-22, 07:48 AM
