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Ask Jason Whatley Your Own Question
Jason Whatley
Jason Whatley, HVAC Technician
Category: HVAC
Satisfied Customers: 60
Experience:  HVAC/R Supervisor at DOJ
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I attempted to connect based on your input and I am blowing

Customer Question

Jason I attempted to connect based on your input and I am blowing the circuit board fuse
Submitted: 1 year ago.
Category: HVAC
Expert:  BillyHvac replied 1 year ago.

Hello, my name is Billy.

I hate to give conflicting info but it is NOT recommended to wire the humidifier into the gas valve circuit.

Also we will need to know humidifier maodel number as some Aprilaire units use their own built in transformer which would conflict with HUM terminal.

So, what model humidifier?

What wiring was used before to humidifier?

And yes you are correct...we should not need a current sense relay.

Customer: replied 1 year ago.
Aprilaire 400M
Customer: replied 1 year ago.
I previously used a current sensing relay and worked fine but the humidifier no longer works. I want to make sure I have the wiring correct before I replace a possible bad solenoid valve.
Expert:  BillyHvac replied 1 year ago.

Ok, you have a basic flow through with a simple 24v solenoid.

Now there are various ways to wire. The most common is HUM and C..

The hum goes to humidistat

out of other humidistat terminal to solenoid and from remaining solenoid wire back to C.

As a test..turn power off..

Run a wire from R and C..

Attach R to one solenoid wire and C to to other...the solenoid should react as it will have 24v constant.

Then we can go from there

Customer: replied 1 year ago.
Unfortunately I don't have the chance to do this now.
Expert:  BillyHvac replied 1 year ago.

no problem...just wait until you can attempt and then respond.

Keep this on your end as any response from you forces a response from me.

Billy

Customer: replied 1 year ago.
Hi Billy, if I wire using the HUM connection will the humidifier only run during HEAT mode? Is this not the same as connecting to the W terminal?jim
Expert:  BillyHvac replied 1 year ago.

Hum = operation in heat mode.

We do not want W terminal as that puts it in the same circuit as the gas valve. Basically this adds another "load" in the gas valve circuit.

The HUM is dedicated circuit for humidifier. To wire in the W (gas valve circuit) would work but is strongly frowned on as it can affect the heat circuit.

Ask anything you need to know...

Customer: replied 1 year ago.
Billy, I am just now getting to try this. I wired it as you stated and I am blowing the fuse on the board when the humidifier kicks on.
Expert:  BillyHvac replied 1 year ago.

please post pic of the humidifier here with front off.

Customer: replied 1 year ago.
attached is a picture of the furnace board. I am blowing fuses when the humidifier turns on. Can we talk on the phone?
Expert:  Jason Whatley replied 1 year ago.

Hello, Billy has opted out of the question so now I can help you again. Have you tried the original diagram that I sent you? ( Sorry you are getting conflicting information here - Aprilaire specifically gives you the option to use the w terminal because the solenoid has a very low volt amp rating)

Expert:  Jason Whatley replied 1 year ago.

If you are blowing a fuse when the humidifier is turning on, you have a short in the humidifier circuit. Recheck all of the wiring and make sure there are no nicks in the wire jacketing too.

Expert:  Jason Whatley replied 1 year ago.

IF all wiring is good - when Billy had you run a pair of wires from r and c to the humidifier, the fuse blows then the solenoid valve itself is suspect of the source of the short.

Customer: replied 1 year ago.
i just replaced my humidifier with a new one thinking the solenoid valve was bad.
Expert:  Jason Whatley replied 1 year ago.

And the new one is blowing the fuse?

Customer: replied 1 year ago.
hold on I'm going to rewire based on using the W terminal
Expert:  Jason Whatley replied 1 year ago.

Okay. Did you run all new wiring to the new humidifier? If any piece of the wiring is skinned or touching the ductwork or both wires touch each other it will ground out and short. It's most common to find a short in the wiring from a bare spot touching metal

Expert:  Jason Whatley replied 1 year ago.

I see the picture you sent of the furnace circuit board, is this a Bryant/Carrier/Payne furnace? Also a picture of the humidifier and the humidistat would be really helpful.

Customer: replied 1 year ago.
ok i just wired just like this drawing. I am waiting for the furnace to fire up and then ill turn on the humidifier. Yes its a Carrier Furnace.
Customer: replied 1 year ago.
just blew another FUSE and now i am out of fuses!!! this is awful
Expert:  Jason Whatley replied 1 year ago.

can you send me a picture of the humidistat with the cover off and a picture of the humidifier with the cover off?

Expert:  Jason Whatley replied 1 year ago.

I know these shorts are trying, but we will get it straightened out

Customer: replied 1 year ago.
added pics of humidifier and humidistat
Expert:  Jason Whatley replied 1 year ago.

The diagram you followed is correct for a conventional humidifier and humidistat like the Aprilaire 400m with dial humidistat. We need to be certain there are no shorts in the wires themselves.

Expert:  Jason Whatley replied 1 year ago.

Okay got the pictures. Can you send a picture of where the wires splice into each other? ( I see the humidistat is wall mounted and has a red and white wire to it, and the solenoid has two white wires to it)

Customer: replied 1 year ago.
I had to go to store to get fuses and they only have two. I can't afford to blow any more since its going to be double digits. Can we do this by phone?
Expert:  Jason Whatley replied 1 year ago.

Unfortunately I'm not set up for phone right now. If you want to wait until you can get more fuses that's fine with me. Just so you're not out of heat for the night

Customer: replied 1 year ago.
I should have them in about 20 minutes
Expert:  Jason Whatley replied 1 year ago.

No problem

Customer: replied 1 year ago.
ok I'm back heres a pic of the wiring at the humidifier
Expert:  Jason Whatley replied 1 year ago.

Okay, so the white wire goes straight to the solenoid valve, and the red goes up to the humidistat and back from the humidistat to the solenoid valve?

Expert:  Jason Whatley replied 1 year ago.

Do you have a volt meter available?

Customer: replied 1 year ago.
no volt meter
Customer: replied 1 year ago.
Yellow wire from solenoid valve is wired to 24V common on furnace board, W from furnace board is going out to HSTAT, other HSTAT wire is going to other solenoid connection
Expert:  Jason Whatley replied 1 year ago.

That's exactly how it should be. Try this one more time - turn off power and disconnect humidifier wiring from solenoid valve and circuit board. Run one wire from c terminal to one leg of solenoid valve. Run one wire from r terminal to the other leg of solenoid valve. Restore power and listen for the solenoid to click. This will verify the solenoid valve is not shorted (I know it's new but I've seen it before)

Customer: replied 1 year ago.
i did that and the solenoid didn't click on.
Expert:  Jason Whatley replied 1 year ago.

did it blow the fuse?

Customer: replied 1 year ago.
take a look at this wiring diagram. It shows 2 white wires coming from the humidifier one of them connecting to the solenoid valve. It came out of the box wired this way. Is that correct?
Customer: replied 1 year ago.
no it did not blow the fuse
Customer: replied 1 year ago.
crap hold on I didn't replace the fuse. Let me test again.
Customer: replied 1 year ago.
OK! the solenoid clicked on
Expert:  Jason Whatley replied 1 year ago.

Okay, that verifies that the solenoid is good. Now, that also tells us there's a short in the wiring somewhere.

Customer: replied 1 year ago.
I checked all the wires and they look good, nothing has changed since I installed the first unit last year.
Expert:  Jason Whatley replied 1 year ago.

Okay let's try this... Turn off the power, Replace the wires as they were, disconnect the wires from the humidistat on the wall. Take those wires at the humidistat and tie them together. Restore power and see if fuse is good when the runs (solenoid will click then too when heat comes on if the fuse doesn't blow). This will tell us if the humidistat is causing a problem.

Expert:  Jason Whatley replied 1 year ago.

Very doubtful but this is the only way to troubleshoot without a volt meter

Expert:  Jason Whatley replied 1 year ago.

Can you send a picture of the humidifier without the filter panel in? Do you have those white wires that the diagram shows?

Customer: replied 1 year ago.
here you go
Customer: replied 1 year ago.
i just did that wiring you suggested and as soon as i turned on the power the fuse blew
Expert:  Jason Whatley replied 1 year ago.

So it's not the humidistat. And you have it wires exactly like the diagram shows with the white wires? (That is an overflow switch in the bottom of the unit)

Expert:  Jason Whatley replied 1 year ago.

Try taking the white wires out of the sequence.

Customer: replied 1 year ago.
i'm down to 2 fuses and need at least one. I don't know what bypassing the white wires will do?
Customer: replied 1 year ago.
i give up
Expert:  Jason Whatley replied 1 year ago.

Just to verify the overflow switch isn't causing the issue (doubtful again). I'm definitley positive there's a short in the wiring - we've proved that. What I would suggest is running new wiring from the furnace to the humidistat and back from the humidistat to the humidifier. There is a short, somewhere

Expert:  Jason Whatley replied 1 year ago.

Its very hard to tell without a volt meter to check continuity with

Customer: replied 1 year ago.
I cant to anymore tonight. I am going to have to call a contractor
Expert:  Jason Whatley replied 1 year ago.

Try the wiring before calling for someone to come in. I'm confident that will save you $$$!

Expert:  Jason Whatley replied 1 year ago.

When you have time of course. I'll be hear waiting to hear if you got it! :)

Customer: replied 1 year ago.
son of a bitch. i used the spare thermostat that came with the new unit and wired it up and now it works. somehow there's a short in the line!!!!
Expert:  Jason Whatley replied 1 year ago.

Awesome, I knew there had to be somewhere

Expert:  Jason Whatley replied 1 year ago.

Probably a small pinch that you can hardly see

Customer: replied 1 year ago.
Thanks for sticking with it
Expert:  Jason Whatley replied 1 year ago.

For sure! That's what I'm here for

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