Aprilaire humidifier install

I'm installing an Aprilaire 600a on my antique [well- 1980 or so] Sears? furnace.
So of course it doesn't have an 'eac' or 'hum' terminal. We don't use it in 'fan only' mode anyway, so I thought it would be an easy task to just hook the wires to the fan relay so the humidifier is active when the fan is running.
I haven't hooked it up yet because I don't want to fry my electronics. So I put my tester on what I thought would be a 24v fan circuit- but I get no reading. . .
Operator error- or wrong assumption? Here's a picture of the Honeywell R8184 relay
http://i289.photobucket.com/albums/ll235/elbrecht/honeywell.jpg
I expected to find 24v on 'C' and 'G' - but get nothing. I tried the AC scale, too just to see if I misunderstood the schematic. I get a zero reading on that scale, too.
Can anyone tell me where I want to hook the humidifier to let it know when the fan is on?
The humidifier 'installation instructions' show two wires hooked either to "Hum" and common- or to 'W' and common.
Thanks, Jim
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wrote:

Yes, you should see ~24 VAC between G & C when the thermostat is calling for heat. Was it when you did the test?
Paul F.
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-snip-
Yes- and I tried reversing my leads. I'll give it a go again tomorrow. I just wanted to make sure I wasn't missing something obvious.
Thanks, Jim
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Didn't they provide a little transformer? You really should get the power from the blower circuit, so that the humidifier doesn't run during the warm up period when the heat exchanger is coming up to temp. Though, in reality, it won't make a lot of difference.
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On Wed, 29 Oct 2008 21:08:35 -0400, "Stormin Mormon"

Yes- The transformer goes to a couple other terminals that need power 24/7. There are 8 terminals in all.

I think I've got it now- thanks, Jim
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Jim Elbrecht wrote:

a Thermopride. I suspect it is wired in a similar fashion to yours. Your photo is of what Honeywell refers to as an Oil Burner Control. It has a relay inside but it is not the relay you want to hook the AprilAire to. If you look you should find a Control Center (Honeywell R8285...the suffix will probably be A or B). Since you aren't using the fan (G) lead, the best way is to get a model 50 Current Sensing Relay from either AprilAire or GeneralAire and use that to control the 24 volt signal to the humidifier. As I recall I paid about $18 for the one I bought.
All voltages coming from your thermostat will be ac. Measure using C as your reference and from C to R should measure 24 vac, +/- (this is the source.) C to W only when calling for heat will also be 24 vac. When your thermostat's Fan switch is in the manual position then C to G will measure 24 vac. Your blower is probably being turned on using 120 vac by the Fan and Limit Control, Honeywell L4064, which is most likely connected through the Control Center relay to the blower.
Boden
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-snip-

Aha- I found that one. I'm guessing the fan terminals on the one I photographed sends a pulse to the other relay which switches the power to the fan.

Looks like a transformer will be about the same. and I'll still be able to use the 'change your water panel' idiot light. Tony recommended hooking it right to the blower power leads.

I just noticed that the schematic has 3 wires to the t-stat. I have 2- W & R. I get 24v on c-r constantly. [also R & a few others, but I've forgotten the details already]
I replaced that part 6 yrs ago- but copied the wiring that had been existing for 15 yrs previous.

Looks likely- that's probably where I'll tap into the blower power when I get the other transformer..
Thanks for your thoughts- Jim
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-snip-

That's where I ended up going. Had a handy utility box already mounted to tap into it. Bought a transformer at Lowes for $15. Wired it up and all is well.
Thanks all- Jim
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Jim Elbrecht wrote:

Dom't try to tap 24V AC from the 'stat circuit. Use provided 24V transformer connected to blower power leads. I installed 700a about a month ago replacing old Lennox spray type humidifier. BTW, AC current is not polarized. Reversing meter leads is meaningless!
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-snip-

I think this is the way I'm going to go- but I'll need a new transformer. The provided one needs to provide constant power & is wired to a different circuit.
-snip-

<Smacks self in head> Until I read that I was *expecting* the 24v to be DC, but was checking for AC & DC on the terminals.
Thanks, Jim
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