Too Long for Blower to Start ?


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Old 12-11-16, 09:57 PM
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Too Long for Blower to Start ?

I have Bryant 394gaz furnace circa 1990. Its operating fine. Im just wondering if it should take 90 sec for blower to start up after the burners fire? The burners normally fire for only about 6 minutes for 1 cycle. So the warm up portion is about 25% of the cycle. Seems high to me but I'm not a furnace expert.

Is there something I can check to determine if warmup should really take 90 sec?
 
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Old 12-11-16, 10:52 PM
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Is there a control board in that furnace ? Can you post the model number from it.
 
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Old 12-12-16, 08:41 AM
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The igniter control (gray box above gas valve) is LH33WZ512A.

I guess the control board is in the box with the yellow sticker in the blower area. It is 306022-201 Rev. A
 
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Old 12-13-16, 06:08 AM
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6 minute burn with outside temps in the low 20's? Someone is going to say that's a short cycle and your furnace is too big but I'd sure like to trade with you. Mine takes about 15 minutes to raise the temp 1 degree.
 
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Old 12-13-16, 06:36 AM
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It's very hard on equipment to cycle so frequently. It should first be determined if the unit is cycling off on a safety or the thermostat.
A furnace that age should also have the heat exchanger inspected
 
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Old 12-13-16, 06:50 AM
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I'm trying to ascertain what blower control you have. It appears that it's a timed system with the on delay programmed for 75 seconds.
 
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Old 12-13-16, 09:53 AM
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Outside temp 24F, no wind
Stat set at 69F
Furnace is 150 btu in, 80% (I'm told) so 120 btu out. Im also told it is bigger than necessary.
3500 sf colonial in SE Michigan.

Today's cylce times:
Stat issues heat demand
Pilot lights immediately.
40 sec later burners fire.
75 sec later blower starts
about 7 minutes later stat heat demand satisfied and burners shut off
110 secs later blower shuts down.
15 minutes later, stat issues another heat demand and cycle starts again

So thats about 25-26 minutes per cycle.

Note: I have a Sensi wireless stat which allows me to monitor stat demands on my phone (pretty cool I think). It also allow me to adjust cycle duration fast/med/slow. I have it set to slow.

Recently replaced pilot (its the type with the bi-metal switch, LH680005) which I diagnosed myself I'm proud to say. Now the above cycle is 100% reliable. Before new pilot, the burners would shut off several times before blower started and sometimes burners shut down when blower started.

Now seems to be running perfectly.

PJMax - looks like your were right on with 75 sec time delay. Thanks. Wish there was a way to shorten that delay as the warm up time is 15% of total burn time. Potential gas bill savings?
 
 

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