Blower does not shut off


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Old 10-18-09, 10:09 PM
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Question Blower does not shut off

Greetings,

Disclaimer: Please pardon my ignorace as I'm a first time homeowner with no HVAC/electronics experience thus please be considerate and detailed in your responses

I've been doing research for several hours now but have questions which have not been answered in my queries.

What is happening:
I have an old Bryant gas AC/furnace that has started acting up. It ran ok for about a day or two, went through series of on/off/mini-explosion and now the blower never shuts off. Furnace does function as expected otherwise:
- pilot stays on
- burners ignite
- temperature set in thermostat is attained
- burners shut off
Only issue is that the blower never stops. Only way is to cut the power using the service power switch.

What I've done:
- set thermostat to auto
- replaced air filter
- cleaned the pilot
- cleaned the limit control (sensor and terminals)
- removed the control box and measured voltage:
Line-1 = 19.9V
PR-1 = 3.9V
SEC-1 = 3.9V
Limit Control terminals = 3.9V

My logic:
From my research I've gathered that PR-1, SEC-1 and Limit Control terminals should read ~24V, and if not, transformer is likely the issue. I know nothing about transformers but don't they usually reduce Voltage by specific percentage of the power supplied? Reason I ask, 115V to 24V is ~5x reduction. 19.9V to 3.9V is ~5x reduction. Additionally, transformer looks visually sound, no burnt areas or anything like that. I have no wiring diagram but should Line-1 be 115V? I'm thinking that if it was then transformer would reduce Voltage ~5x to about 24V, Limit Control would have ample power and blower would shut off as a result. Is the control box not getting enough power? I find that hard to believe but by above logic it seems that transformer is doing its job.

Your help is greatly appreciated - I have learned a lot this weekend
 
  #2  
Old 10-19-09, 12:01 AM
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Very likely your furnace circuit diagram is similar to Figure 4 in the following website:

http://www.xpedio.carrier.com/idc/gr...i394g-25-1.pdf

The voltage between Primary 1 and Primary 2 should be 120 VAC or thereabouts. Between Secondary 1 & 2, 24 VAC.


When you push down the plunger switch in the fan compartment, do you hear a fairly loud "click" as the heater fan relay makes ---- which shuts the fan OFF?

No click and the fan will stay on.
 
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Old 10-19-09, 07:19 AM
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SeattlePioneer, thank you for your reply.

Indeed figure 4 resembles my PCB, thank you for this.

Here is where my ignorance becomes apparent. When I measured voltage last night I would connect one prod to ground (furnace case) and the other to "hot terminal" (Line-1, PRimary-1, SECondary-1, etc) which produced before-mentioned values. I've just measured voltage between PR-1 and PR-2, followed by SEC-1 and SEC-2 and values were 124V and 29.8V respectively. That rules out the transformer as the culprit, no?

I do not hear a click, and I know exactly the sound you're talking about as it is fairly loud. Where would I find this heater fan relay and how can I go about testing it?

Thanks again.

EDIT: Looked at the wiring diagram again and my guess is that it's the component marked HFR How would I go about troubleshooting it? I seem to recall people giving it a tap in hopes of braking the contact so I gave it couple taps but was met with a "lightning display" inside of its plastic case. I'll wait for some responses before I make things worse.
 
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Old 10-19-09, 08:33 AM
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Yes, your test proves that you have the correct voltages going into the transformer and coming out of it.


Carrier circuit boards of the kind you have energize the heating fan relay whenever the power is on to the furnace. But energizing the relay turns the fan off, not on.

As long as you have power to operate the fan, what OUGHT to happen is that when you push in the fan compartment plunger switch, you hear the click and the fan remains off.

Since you hear no click and the fan turns on, you have a bad circuit board that needs to be replaced.

Don't muck around trying to replace the relay. One of the advantages of this system is that you renew a lot of other components and systems that are also on the circuit board, avoiding other problems in the future.
 
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Old 10-19-09, 11:08 PM
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Replacing entire PCB makes sense - I don't mind spending a little more to avoid problems. Last question would be, which circuit board to buy? Model number on the control box states: 306022-201 Rev.A

What makes this challenging is that there is no model number on the unit (I'm talking about the furnace, not PCB). Previous owners left me with nothing; no model number (sticker ripped off), no wiring diagram, nothing I googled for the PCB model with little success. Most I got is that this supposedly replaces my board, but there is no way for me to be sure since most websites list their items by furnace model.

Anyone with 306022-201 Rev.A PCB care to tell me their furnace model?

Thank you
 
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Old 10-21-09, 08:43 AM
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Noone knows what current circuit board is equivalent to 306022-201 Rev.A ?
 
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Old 10-21-09, 10:29 AM
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Have you tried calling an HVAC - mechanicals supply house? In our town here not only can you talk to the city desk guys, but people who are specialists in their own cubicles or suites, like their heating dept.
 
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Old 10-21-09, 06:50 PM
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Post some pictures of your furnace and the circuit board. Someone may recognize it.
 
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Old 10-22-09, 12:17 AM
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Maybe these will help - thanks again for all the help.





 
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Old 10-22-09, 07:30 AM
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Carrier makes Carrier, Day and Night, Payne and Bryant model furnaces, and any of those brands might have been slapped on your furnace.


The model for your furnace is GAW

So, look for a distributor for one of these brands and tell them you need a Payne GAW circuit board or equivalent.

Also, most heating repair companies should have one of these available since the furnaces are so common.

You can certainly find them for sale on line as well if you wish.
 
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Old 10-22-09, 08:34 AM
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There does not appear to be a fan timer control on or off that board. What is that silvery square above the gas valve. The fan/limit control? - and maybe it is getting stuck in there, or some bimetal disc is weak?

You should be able to test, when the blower keeps running on, if current is still going through that switch when it should not be, once the furnace cools down to say under 85 degrees and less.
 
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Old 10-22-09, 10:07 AM
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Originally Posted by ecman51`
There does not appear to be a fan timer control on or off that board. What is that silvery square above the gas valve. The fan/limit control? - and maybe it is getting stuck in there, or some bimetal disc is weak?

You should be able to test, when the blower keeps running on, if current is still going through that switch when it should not be, once the furnace cools down to say under 85 degrees and less.

The silvery square is the limit switch with light reflecting off of it. The fan is controlled by a timer on the circuit board.

In this case, the heating fan relay energizes the fan when the relay is in the normally open position, and shuts the fan off when the relay is closed (DPDT relay).

When the 120VAC is applied to the furnace you should hear a "clunk" as that relay closes, keeping the fan off. Since no clunk is being heard when the door switch is pushed in, that suggests that the circuit board is defective.
 
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Old 10-22-09, 10:18 AM
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One other thing I see --- you have a wire connected to the Gc terminal on the circuit board.

Where does that wire go to?


Measure the AC voltage from Gc to C. If it's 24 volts or thereabouts, that will turn the fan on and keep it on.

Disconnect the wire to Gc at least temporarily and see if that shuts off the fan.
 
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Old 10-22-09, 10:52 AM
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I'm at work and I don't have my cheat sheet with me to know what those symbols mean but Y GC R W all have thermostat wires connected to them (you can see they're thiner). I will measure Voltage when I get home...but I didn't change wiring at all so by your logic that would mean that there was no 24 Volts between GC and C before. Can Voltage change like that?

Thanks again
 
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Old 10-22-09, 01:30 PM
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The thermostat may have a switch which energizes that contact and thus runs the fan. Sometimes the switch is labeled with "auto" and "on" positions, or it might be identified other ways.


Even so, you should still hear that "clunk" as the HFR relay closes when the power is switched on to the furnace and the fan compartment door switch is closed.

Since that isn't happening, it still suggests a bad circuit board to me.
 
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Old 10-22-09, 03:54 PM
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Could the limit circuit be open? He could easily test at limit itself or where I see near the top right corner area of the control board, LIM....
 
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Old 10-22-09, 06:21 PM
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Hello Ecman,


The most common reason for the fan to run continuously on this kind of furnace is for the limit switch or one of the other safety switches to open. That interrupts the 24 VAC circuit to the HFR (heating fan relay) which turns it off and causes the fan to run continuously.


But in this case the burners and pilot are operating normally, so we know that the 24 VAC circuit is OK.

That being the case, the HFR should be energized with it's distinctive "clunk" every time the burner door switch is depressed, energizing the HFR which closes the relay, shutting off the fan motor.

These Carrier furnaces have these peculiarities. The good thing about them is that if you understand them it helps to isolate what the problem is likely to be.

My recommendation is still to replace the circuit board.
 
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Old 10-23-09, 09:36 AM
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Originally Posted by mpz81
control (sensor and terminals)
- removed the control box and measured voltage:
Line-1 = 19.9V
PR-1 = 3.9V
SEC-1 = 3.9V
Limit Control terminals = 3.9V

My logic:
From my research I've gathered that PR-1, SEC-1 and Limit Control terminals should read ~24V, and if not, transformer is likely the issue. I know nothing about transformers but don't they usually reduce Voltage by specific percentage of the power supplied? Reason I ask, 115V to 24V is ~5x reduction. 19.9V to 3.9V is ~5x reduction. Additionally, transformer looks visually sound, no burnt areas or anything like that. I have no wiring diagram but should Line-1 be 115V? I'm thinking that if it was then transformer would reduce Voltage ~5x to about 24V, Limit Control would have ample power and blower would shut off as a result. Is the control box not getting enough power? I find that hard to believe but by above logic it seems that transformer is doing its job.

Your help is greatly appreciated - I have learned a lot this weekend
I had to reread the 1st post SP. Yes, I agree.

It does seem like Line 1 should be 115, I do believe. I do not believe they use "Line" terminology for step-down voltage. You'd think any board connection would say "trans", at the 24 volt hookup terminal.

I see his line voltage enters furnace at the far right in bx cable. He needs to trace line 1 wire. I'm thinking his theory, in his above quote, is correct.
 
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Old 10-23-09, 09:50 AM
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I emailed one store and reply I got was that the board I provided link to in post #5 is indeed the PCB that replaces my dinosaur. We'll see I suppose. I'm going to do a little more research on it tonight and buy it tomorrow if I find no reason to look for something else.

This thread is already page 1 on google so I hope that it helps others with similar issue. BTW, this circuit board can be had for about $100
 
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Old 10-23-09, 09:56 AM
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Quick. Before you buy that board -where does black Line 1 come from? In your photo I lose sight of it as it heads downward.
 
 

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