Problem Using Aquastat to Control Fan


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Old 11-19-11, 01:37 PM
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Problem Using Aquastat to Control Fan

I have a gas boiler that feeds a hot water tank and a finned coil heat exchanger inside a forced air furnace via PEX tubing. I have my thermostat set up to turn on the boiler pumps and bring the heat exchanger up to temp (~170 F) and I am trying to use an L6006C aquastat to control the fan on the furnace. I have my hot wire from the fan leading to the R and the neutral on the B. my problem is that I have the temperature on the aqustat set at 170deg with a 10deg differential but the furnace keeps running to below 120deg and by this time the fan is blowing cold air. Any thoughts as to what is wrong with this setup? Also I tried having it set up as R to W but this turns the fan off after 120 or so deg.
 
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Old 11-19-11, 04:05 PM
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If you have the aquastat attached to PEX pipe it is not going to sense the temperature very well. The bulb needs to be attached to metal (preferably copper) pipe. In your case you may need to go to a remote bulb style aquastat. I also don't understand how you have the aquastat wired into the R/W or R/B terminals of presumably the thermostat.
 
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Old 11-19-11, 04:24 PM
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Grady,
I have two wires that come from the fan that I am using on the aqustat. My thought, and the way I currently have it wired, is when the thermostat calls for heat it turns the circulating pump on, then when the water in the line reaches temp the fan will turn on, thus only blowing hot air into the room.
 
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Old 11-19-11, 05:15 PM
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From where is the fan power coming? There has to be a relay somewhere which sends power to the fan via the aquastat. A photo of the wiring diagram on the air handler would be most helpful.
 
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Old 11-19-11, 05:16 PM
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Grady is correct, you MUST have the sensing bulb securely attached to a METAL pipe and that connection needs to be insulated as well.

Read this pdf on the L6006 to understand the wiring and how to adjust the differential setting if your control has one.

http://customer.honeywell.com/techli...0s/60-2104.pdf
 
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Old 11-19-11, 05:46 PM
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OK, you have 120VAC directly wired to the blower in the air handler, and being switched by the 6006, right?

I think you will need another relay as Grady is suggesting, that is triggered when there is a heat call, wired in SERIES with the 6006.

That way, when the thermostat calls, the relay will close but the fan won't run until the coil gets hot. Then, when the heat call ends, the blower will shut off right away.

Mounting the aquastat bulb on metal pipe might do the trick also... but if not, you have this option.

One thing you should check... according to the specs on the 6006, the switch is rated for EIGHT AMPS. Make sure that your blower is not drawing more than the rated current! If it does, you will need to add yet another relay to carry the current.

Also, you said:

I have my hot wire from the fan leading to the R and the neutral on the B.
This sounds wrong to me... potentially dangerous...

The HOT wire from the blower to the aquastat is fine... but the HOT SUPPLY should go to the aquastat, NOT the neutral. You want to switch the HOT wire. The NEUTRAL should go to the neutral wire on the blower.
 
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Old 11-19-11, 07:20 PM
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I note that you have a hot water heat exchanger installed in a hot air furnace and you are trying to get the fan to come on when the heat builds up in the plenum i suggest using the original fan control to turn blower fan on and off.
 
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Old 11-19-11, 07:35 PM
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If the fan control is a fan/limit it's likely upstream of the hydronic coil & if it ever got hot enough to bring on the fan, as soon as the fan came on the air flow would cool the control enough to shut the fan off.
 
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Old 11-19-11, 07:50 PM
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If the heat exchanger has the same btu out put as the hot air furnace it should operate as if the furnace burner is on.
 
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Old 11-19-11, 08:18 PM
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connections

are these RWB connections on the fan control or the thermostat?
do you have a line voltage thermostat???
 
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Old 11-20-11, 07:45 AM
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saves, I don't think your 'getting it'... if it's a FURNACE being converted to a 'hydro-air handler' by the installation of a water to air heat exchanger in the plenum ABOVE the original air to air heat exchanger of the furnace, then the original fan limit switch will NEVER get hot enough to switch the fan on. As Grady said, if by some very remote chance the switch IS tripped by the coil above, as soon as the blower turns on again it will cool the switch and the blower will shut off again, almost immediately.

Hvac, the R W B are the terminals on the L6006C aquastat.
 
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Old 11-20-11, 03:17 PM
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Thanks all for your replies and help,
Just for clarification the fan/furnace was originally built for an outdoor corn burning furnace so it has the finned heat exchanger built in, if that makes any sense. I have two wires coming out of the furnace that will turn the fan on when touched together. I took into account the temperature difference of the PEX tubing and set it to around 120 deg while wired to R/W and it seems to be running well.
 
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Old 11-20-11, 04:18 PM
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I would make life simple and buy a Taco Hydroair control. It works on a timer.
http://www.taco-hvac.com/uploads/Fil...ry/102-093.pdf
 
 

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