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airheatman, HVAC Technician
Category: HVAC
Satisfied Customers: 8385
Experience:  Furnace, A/C and heat pump specialist.
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I have a aprilaire 400 and am tracking down two spare wires

Customer Question

I have a aprilaire 400 and am tracking down two spare wires (yeah I know)
JA: I'll do all I can to help. How long have you been dealing with this?
Customer: This has been like this for awhile. Hence my confusion. The yellow wires are hooked to solenoid so thats good. From quick search I am believing these are for a transformer that I have missing for some unknown reason. Wires go to inside of my Carrier heatpump
JA: Did you double-check the thermostat's settings? And what about the filters?
Customer: I have not looked at operation of humidity control on thermostat. There is obviously something not hooked up and I am kicking myself for not taking notes. Not even sure why it was removed If its the transformer
JA: Do you plan on doing the work yourself?
Customer: At this point hopefully yes. I didnt alter anything so I believe I just have to identify the transformer that I need to get
JA: Anything else we should know to help you best?
Customer: WEll, just verifying that this unit came with a transformer for install?
Submitted: 11 months ago.
Category: HVAC
Expert:  airheatman replied 11 months ago.

OK first let me gather a bit more information.There are a couple of ways to control the Aprilaire. One is using a humidistat on the wall near the thermostat and the other is using a thermostat which included humidity control feature.Also many newer furnaces are equipped with a terminal for adding a humidifier.

So let me get this info:

1.Whether using tstat with hum capability or a separate humidistat on wall by tstat

2.Model on furnace or air handler

3.Model on thermostat

4.Any pcs of current wiring at thermostat,humidistat or furnace will prove helpful.

Customer: replied 11 months ago.
1. It is being controlled by a seperate Carrier Thermidistat control. The humidity portion displays on the control. Current relative humidity indoors is 53%
2. Indoor portion of heat pump (air handler) is Carrier Model #FV4BNF002
3. Carrier Thermidistat (all is about 10 yrs old)
4. Has two spare wires, One is going to coil (rated 24vac so guess i dont need a transformer) and the other is a pinkish wire going into wiring going to thermidistat
Expert:  airheatman replied 11 months ago.

Give me model on Carrier humidistat

Customer: replied 11 months ago.
It has no model number explicitly stated. There is a number on the back of the door###-##-####2
Expert:  airheatman replied 11 months ago.

OK all that should be needed is a wire from common at furnace to the solenoid on the humidifier , a wire from R on furnace to humidifier and then a wire out of humidistat to solenoid on humidifier

Expert:  airheatman replied 11 months ago.

See below

Customer: replied 11 months ago.
Right now there is two yellow wires coming from the solenoid. Each of these are wire nutted to a white wire going into the humidifier (assume for float reading). I assumed coil wire (24v) energizes the solenoid when the other wire (pinkish) indicates that humidity is low? So I need to know which of the wires (24v) and humidistat control go to which yellow wire :)
Customer: replied 11 months ago.
That is why I was searching on aprilaire site to see if I needed a transformer and where these wires went :)
Expert:  airheatman replied 11 months ago.

You would only need a transformer I not using the furnace transformer .Older furnaces only had a 20vs which was not enough to handle relays in furnace and humidifier.Newer furnaces all use a 40va which is plenty big enough for both.

Customer: replied 11 months ago.
Yep. Figured that when I saw one of unknown wire went to coil with 24v output. Am I missing a relay or something. It looks like something should apply 24v to solenoid when a signal comes from the humidistat :)
Expert:  airheatman replied 11 months ago.

That is correct The 24v is constant to humidistat. When humidistat sense need for humidifier, it closes contacts completing circuit to humidifier, much as a light switch works

Customer: replied 11 months ago.
Yeah the humidistat is getting 24v from a wire that is wirenutted to one of the spare wires
Customer: replied 11 months ago.
Note that the two spare wires have been used. They are both stripped with a bare wire that obviously was attached to something
Expert:  airheatman replied 11 months ago.

You should not need a separate relay.The solenoid is like a light bulb.

It has one leg directly from transformer.The other 24v wire goes to humidistat and when humidistat calls for humidifier, circuit closes and completes circuit to solenoid just a a ligh switch would to the bulb.

Can you attach some photos of what you have?

Customer: replied 11 months ago.
Customer: replied 11 months ago.
Blue wire goes to 24v. Pinkish wire goes to humidistat. First pic shows brown wire that has red and white wire that are wirenutted to those two wires
Customer: replied 11 months ago.
The mystery wires are routed outside of the air handler unit on side by humidifier
Expert:  airheatman replied 11 months ago.

I am wondeing if maybe they used to go to an outdoor sensor.

Customer: replied 11 months ago.
Would an outdoor sensor need voltage?
Expert:  airheatman replied 11 months ago.

No it would just go to the humidisat and open and close by temp

Customer: replied 11 months ago.
Well one of the wires is definitely 24v and is wirenutted to another blue wire that goes to thermidistat :). It has to energize that solenoid in some way. I am not guaranteeing that the white wires are correct.
Expert:  airheatman replied 11 months ago.

I am going to open this to other experts who may be able to help.

I have opted out of the question to see if perhaps other experts may have more information and can assist.Please do not rate or reply as that will send question back to my desk and delay getting assistance..Please stand by to see if another expert can assist further.Leaving a poor service rating will not automatically refund your money. You have to request a refund if not satisfied with the information provided being accurate.

If no expert can help and you are unsatisfied, we can request a refund of your deposit

Customer: replied 11 months ago.
OK thanks. I am away from computer until later this evening so no hurry :) Thanks, Tim
Expert:  airheatman replied 11 months ago.

Hopefully oyhers may have more ideas

Customer: replied 11 months ago.
Might as well get a refund. I think I figured it out.
Expert:  airheatman replied 11 months ago.

No problem , where did they go?

Customer: replied 11 months ago.
I believe the 24v went directly to one yellow wire on solenoid, the other yellow wire on solenoid went to one of the white wires from water level sensor in humidifier, other white wire from float goes to wire to humidistat (ie.. making a circuit when the water level sensor detects that water level is low)
Expert:  airheatman replied 11 months ago.

Gotcha. Thanks for using the service,I will request refund since no one actual picked up the question.Do not rate as that will keep question open