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[Charles Sullivan]

Hey everyone thanks for the info so far. One thing I just thought of would be to replace my service switch at the A/C air handler with  an XPS2 switch, since the transformer for the thermostat side of A/C receives power through this.Am I correct to assume that the XPS2 will behave like a lamp module and stay off until I either manually turn it on or turn back on with a  command from AHPro.
Thanks, look forward to your thoughts on this approach.

I don't see any specification about latching/non-latching for the XPS2 on the X10Pro website, and I don't know of any appliance-type modules which aren't latching.  So without further info I'd assume that the XPS2 does in fact have a latching relay.

You could try calling the X10Pro Tech Support line and inquiring.  These techs seem to be a cut above the ones in standard X10 Tech Support.

[dave w]

wheelsea

I am pretty certain Charles is correct, the XPS2 remains in the same state it was, when power is interupted. I do not have any XPS2, but do use PAM04 for 240 V pumps. I believe the PAM04 and the XPS2 are same animal, inside.
FWIW
The 24V latching relay is the simplest way to go on this. I use 120V coil relays for similar purpose to delay returning power to my home control computer. I use a $5 timing module (electronic surplus price) to relatch the relay 5 minutes after power returns, which (in theory) eliminates all the "flicker and flash" we usaually have as Duke Power brings up the local grid. Works good.

[wheelsea]

Charles, Dave: you are both right . X10Pro support at first gave some conflicting advice on this but then retested and yes it reverts back to the previous state it was on.  Any brand/model # on the 24 volt latching relay and 120 volt coil?
Thanks.

[Charles Sullivan]

Charles, Dave: you are both right . X10Pro support at first gave some conflicting advice on this but then retested and yes it reverts back to the previous state it was on.  Any brand/model # on the 24 volt latching relay and 120 volt coil?
Thanks.

Lest we've confused you about this: The relay we're talking about for your application will be a regular DPST-NO (Normally Open) relay with a current and voltage contact rating sufficient for your Air Conditioner but with a coil designed to pull in with 24 Volts.  It is NOT a "latching" relay, but a normal relay wired so as to keep itself turned on once it is actuated by a momentary contact and as long as the power is on.  A lot of suitable relays will have DPDT contacts, which is fine.  The 120 V coil Dave mentioned was for a different application.

BTW, this assumes that your Air Conditioner runs off 120V single phase.  If its a 230V unit you would normall want to switch both hot leads to it, and would therefore require a THREE-pole relay.
 
There are lots of relays that will fill the bill; the usual problem is how to connect to them and how to enclose them so someone won't get zapped.  Quick connect insulated connectors that you crimp to the wires usually work well for relays which have those  terminals.

Take a look at Magnecraft W92S7D22-24  in their catalog page at  http://www.magnecraft.com/products/e104_sec1_pg40_42.pdf
It's got 30 Amp, DPST-NO contacts and a 24VDC coil.  Quick connect terminals and a mounting flange.  It's listed in a July 2005 Mouser catalog I have as Mouser stock number 528-92722-24, $8.74 + S&H. (Price is probably different now - check on-line at http://www.mouser.com)  You'll still need to put it in an enclosure of some sort and acquire a 24VDC wall-wart power supply and a UM506.

Disclaimer: I suggested a part out of a catalog which looks OK to me, but I'm NOT a licensed engineer or electrician and it may be totally unsuited for your application.  If you're not familiar with wiring and safety practises for power line work, please consult a licensed electrician or someone with experience.

[Oldtimer]

I sense that this kind of wiring is not your forte but, with the caveat that the final responsibility is yours, I'd suggest you use FROOGLE which is part of GOOGLE under "More" on their search window to look up
"24Vac relay DPDT" and order the results from lowest price to highest.  You'll get lots of hits if you do.

I'm concerned that we may not really understand how your 24 volt thermostat control circuit operates.  Charles Sullivan, for example, obviously has a different visualization of it than I do.  The 24 V HVAC thermostat circuits I'm familiar with operate a relay built into the AC or furnace that in turn control the high amperage circuits of the device itself so the relay you're going to add is handling very low current.

Feel free to give us more info as you go along with the hope we can be of more help.

[TakeTheActive]

I'm concerned that we may not really understand how your 24 volt thermostat control circuit operates.  Charles Sullivan, for example, obviously has a different visualization of it than I do.  The 24 V HVAC thermostat circuits I'm familiar with operate a relay built into the AC or furnace that in turn control the high amperage circuits of the device itself so the relay you're going to add is handling very low current.

This "Old Tinkerer" agrees with the Oldtimer  - based solely on my experience with strictly heating (oil at my folks, gas for me furnaces).

You can either interrupt the 120VAC input or the 24VAC output of the transformer that forms a low-current SERIES circuit with the thermostat and the relay (inside a Honeywell Aquastat in my case) whose 24VAC coil, when energized, pulls in the contacts for the 120VAC circulator pump (and another pair for the millivolt feed to the gas valve).

EDIT: How many other "Old Geezer's" besides me find that Spell Checkers DON'T HELP much when you correctly spell the WRONG WORD!!!  (i.e. gas value instead of gas valve - it even LOOKS right the first time around... )

[Charles Sullivan]

You're right Oldtimer and TTA.

Somehow when I got this far down into the thread I ended up with a window AC unit in my mind.