Go Back  DoItYourself.com Community Forums > Electrical, AC & DC. Electronic Equipment and Computers > Electrical - AC & DC
Reload this Page >

How to turn high voltage Air Conditioner on/off via low voltage tstat

How to turn high voltage Air Conditioner on/off via low voltage tstat

Reply

  #1  
Old 10-10-13, 11:31 AM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
How to turn high voltage Air Conditioner on/off via low voltage tstat

Hi, first time poster here.

I've got a ductless mini-split Air Conditioner that's oversized for the room, and it's designed so that the inside (in the house) fan always runs, even when the outside compressor is off (when temp is reached). When this happens, especially spring and fall, the unit immediately starts to SMELL. It was just installed last April, and I'm told there's nothing I can do about it. I got the smallest unit available (9500 BTU), but the room is only 250 sq ft.

As I understand it, the ideal A/C installation is sized to barely keep up, so that it's always working, cooling and dehumifying, and avoiding odor issues.

My idea for non-peak-summer months to set the unit (via it's remote) to the lowest temp (61 F), and slowest fan speed. This will probably always keep the room cool enough (and I can increase the fan manually on the few occasions it does not), but it will take the longest time, which will mimic a unit that can barely keep up with demand.

Along with that, I will need to hook up an existing low-volt tstat (currently part of the whole-house heat solution, nothing to do with this a/c unit), to a relay of some sort (I know nothing about this), which would completely break power to the dedicated A/C unit's circuit, shutting off both compressor and inside fan.

So, the unit always works hard, except when temp is reached, the entire unit stops, and there's no stinky fan running.

I confirmed that when the unit is running, and I shut off the circuit breaker, and back on again, the unit remembers it's low temp, low fan setting. The only odd thing (which doesn't bother me) is that the louver doesn't close (it just lost power). When the unit comes back on, the louver closes, then opens, then starts to run, just like it would recover from a power outage. This seems to be just a cosmetic issue.

The tstat runs to the boiler, which is only a few feet from the electrical panel, wherein lies the a/c circuit breaker.

How do I wire this up? What relay do I need?

Thanks in advance. Any help is much appreciated. Even if I decide to enlist an electrician, it will help to be able to communicate more effectively. Ideally I can do it myself and save on labor, but I want to be safe.
 
Sponsored Links
  #2  
Old 10-10-13, 03:41 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,221
I think all you need is a 2 pole contactor with a 24 volt coil, but my concern would be the odor, what is it? Is it moisture or mold? It may not go away and could remain in the unit. The next time the unit comes on, you'll probably get the odor along with the cooling.

Strictly out of curiosity, what brand is it? Is it a heat pump or does it have other electric heat in it? I may have an application for a mini split.
 
  #3  
Old 10-10-13, 05:03 PM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
Something like this?

Packard C230A 2 Pole 30 Amp Contactor 24 Volt Coil Contactor: Amazon.com: Industrial & Scientific

I've done a bit of reading, but still don't know much about these. How would I wire it up? I assume somewhere I need to attach two tstat wires (hot, common) to the 24v side. For the 120v side, do I need to cut the existing hot leg somewhere between the circuit breaker and the unit, and attach the cut ends to two terminals... across one pole, yes?

I'm confused about the two poles. Are they both on the 120v side? I don't need any 24v connection to be made, right? The tstat should always have connectivity to the relay.

But I only need a single pole on the 120v side, right? I don't need to lift ground when I shut it off, do I?

-----------------------------------------
Not sure if it's moisture or mold. How to tell? The fins are squeaky clean. The unit's been doing this since it was brand new. Does that imply condensate that hasn't yet drained, like what's in the pan (I assume there's a pan, the unit's not very easy to open up and see what's going on).

Oddly, outside the house, the condensate line is always bone dry. Not even a whisper of moisture if you stick your pinky in the end of the tube. No drip marks underneath. Hmm, guess I should attempt to capture in a container, huh.

The unit is a Friedman. It appears to be mounted correctly on the wall, with a very slight tilt towards the side with the piping through the wall.

It does smell a bit still: when it powers up there's a blast of bad breath, and when it's off you can still smell it a tiny bit.

Further thoughts? Thanks.
 
  #4  
Old 10-10-13, 05:46 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,494
Those units come with a very thin drainage tube. My guess would be that it's pinched and not allowing the condensate to run out. That condensate water left in the drain pan would cause that smell.

You would need two people to lift it up carefully off its mounting plate. You don't want to damage the freon lines. Pull it slightly forward so that you can just see behind the unit where the freon/power/condensate lines connect.

As far as wiring. Are you using an existing heating thermostat or a different one ?
A stand alone thermostat would require a separate 24vac transformer. If you intend to use the existing one we'll need to know what wires you currently have on the thermostat.
I'll draw a little diagram for you and update it with your thermostat info. You would be breaking both hot legs and not the ground.
Name:  v.jpg
Views: 859
Size:  11.6 KB
 

Last edited by PJmax; 10-10-13 at 06:02 PM.
  #5  
Old 10-10-13, 08:06 PM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
It's a separate tstat, currently in use for heating. I hope to add the ability to control this a/c unit.

I'll get the wiring for you in a day or two. I'll be offline for an outpatient surgical procedure. Should be pretty loopy tomorrow

Breaking BOTH hot legs. There are two? One for inside, one for outside? Is that right? If so, I'm not yet sure where it splits, as the breaker handles both. I think it may be further down the line, towards the units. Due to tstat wire location, and general convenience of not having to deal with weatherproofing, I hope to connect closer to the breaker box, where I'm guessing it may just be a single hot, if that makes any sense. Then I'd only need a single pole (or half of a two pole). Sound right?

It may take a while to find someone to help me lift the unit, but finding a pinched condensate tube would be the best news ever (assuming I can un-pinch it).

Thanks for your help. Be back soon.
 
  #6  
Old 10-10-13, 08:20 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,494
Your unit should be 240vac. That would mean you have two hot wires.

It's a separate tstat, currently in use for heating.
I'm confused. It would appear that you want one thermostat to do both. You will want the one thermostat to control heat and A/C... correct ?

When you stop back with the wiring available we'll go forward.

Good luck with your medical procedure.
 
  #7  
Old 10-10-13, 11:07 PM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
Sorry for the confusion. Yes, I want to end up with the single tstat that currently serves heat, to handle both heat and this mini-split A/C unit.

It's a Honeywell RTH2300B1012:
RTH2300B1012

Turns out there are only three conductors in the tstat wire. Red, White, Black. Black is unused. Red and White connect to R and W respectively, and R is jumpered to RC. Terminals B, O, G, and Y are unused.

In the utility room, Red and White connect to the heating zone valve & transformer.

I didn't realize 240v consisted of 2x 120. Looks like I can tap into that cable, and mount the relay, on the wall just a few feet from the zone valve in the boiler room.

Can I do this with only three wires in the tstat?
 
  #8  
Old 10-10-13, 11:41 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,494
That contactor needs to be installed in a metal enclosure. It can not be just be screwed to the wall the way it is. It would be a major shock hazard. I would install it in an 8"x8"x6" metal junction box. The boxes come with prepunched knockouts. You must connect the ground to the box also.
Name:  k.JPG
Views: 963
Size:  5.3 KB


At the thermostat you'll be connecting the black wire to the Y terminal. At the other end you'll be connecting the black wire to one of the contactor low voltage connections. Now.... you should see the red wire connected to one of the transformer terminals.... If yes..... then you need to take a piece of wire from the other transformer terminal to the other low voltage lead on the contactor.

Name:  v.jpg
Views: 2251
Size:  13.2 KB
 
  #9  
Old 10-11-13, 12:16 AM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
Thanks for all the info, it's really helpful.

Yes, Red goes to the transformer mounted on the boiler. Red from the second tstat (the other zone in the house, not part of this cooling scenario) also connects there. The other low voltage wire on the transformer connects to one of the yellow wires on each of the two zone valves. And the other yellow (on the zone valve) connects to each zone's tstat White wire.

If I understand the circuit, I use the existing transformer for power to the relay. (But then why do I need a contactor with it's own 24v coil?) In cooling mode, the tstat opens and closes the connection between Y (my black) and R. When the connection's closed, power is supplied to the relay, which then itself closes, providing 240v to the A/C. Right?

What about when I toggle the tstat to heating mode? Will it automatically shut the cooling off (break the Yellow/Red connection)?

Is the relay I linked earlier a good example of what to use?

How do I ground the metal box? Is there a terminal lug inside? Where you show the green 240v common just passing through, really I need to cut it, and connect both ends to the box somehow?
 
  #10  
Old 10-11-13, 12:46 AM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,494
We're sort of going around in circles here. Your link was to a contactor.... let's keep calling it that. Yes... that contactor is perfect for the job.

I use the existing transformer for power to the relay. (But then why do I need a contactor with it's own 24v coil?)
You don't have a relay and a contactor. You have a contactor. You are using the transformer that controls your heat system ONLY because you aren't using both heat and cool at the same time otherwise you would need a bigger transformer.

You are sending power to the contactor to close the contacts. When there is no call for A/C the contactor will not be active and the contacts will be open.

I have no idea what you have there for wiring. I used green as it's the universal color for ground. You may have a bare wire as ground. You will have to cut the wire at the box. It will require you to put in two connectors. You will connect both grounds together and to the box. You can use a one hole lug for that.



I just went back and re-read your first post. This unit was just installed in April. Why haven't you called the installation company to check the condensate/smell issue ? There should be two modes of operation with your A/C. One is when the comp shuts off.....so does the fan. I think that's called economy setting. The other mode is the fan always runs and the comp cycles.
 
  #11  
Old 10-11-13, 01:12 AM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
Thanks again, sorry if I'm mangling the terminology. I think I've got it now.

I did contact the installer about this problem within a week of the installation, back in April. I made the mistake of using a "take the cash and run" guy. He is passive aggressive and has zero interest in supporting his installation.

I've had two other professionals come to look at it, and one had no idea about anything, and the other suggested this idea of the brute force shutoff wiring. I'm waiting to hear how much he wants to install this, but I think he doesn't want the work, and won't be calling me back.

I may call an electrician to do this work, if I have any doubt, but at least I'll be able to communicate more effectively, and identify a very narrow scope for the work, to save on labor.

I may call a fourth A/C guy to check the condensate line as you suggest. I've suggested looking at the condensate flow to all three contractors, but no one either knows how to get in there, or thinks it's a reasonable idea. "It's like a toaster, not really serviceable" says one guy. So, they go home to their house which doesn't smell.

If I can get someone to help me (I'm disabled), I would like to see if I can visually inspect the condensate line myself. Even if I can't fix it, maybe someone can, if I tell them exactly what's wrong.

If there was an economy setting, where the fan shuts off when the compressor is off, I wouldn't need to wire up this jury-rigged system. I'll check again, but reading the manual, calling Friedman, and talking to the fairly knowledgeable contractor #3, who also called Friedman, all point to no such setting on this unit. I hope you're right. I'll check again.
 
  #12  
Old 10-11-13, 05:15 AM
ray2047's Avatar
Group Moderator
Join Date: Mar 2006
Location: USA
Posts: 32,669
Have you tried contacting the manufacturer to see if they can help you directly or can recommend repair people in your area.
 
  #13  
Old 10-19-13, 03:42 PM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
All better now?

Well, I tried to look behind the wall unit to inspect the drain line. Couldn't do it. Decided I'd have to take a more serious approach to figure out how it was connected to the wall.

And now, amazingly, the unit works fine. It must have been a pinched line (thank you for the suggestion!), and I must have fixed it trying to muscle the thing around. Go figure.

The smell is gone, and the outside end of the drain is always dripping. It had always been bone dry before.

Fantastic! Thank you all for your help.
 
  #14  
Old 10-19-13, 04:09 PM
PJmax's Avatar
Group Moderator
Join Date: Oct 2012
Location: NJ - USA
Posts: 43,494
I don't think we ever discussed the brand but you should have been given an installation manual/operating instruction package.

There is a plate or bracket mounted ahead of time to the wall. The inside unit is basically just hanging on that bracket. Some have a screw or two at the bottom from keeping the unit from being lifted up by accident. Most just stay there from the weight. Don't attempt to lift that off the wall yourself.

The best way to do it is to use two people. One at each end. Most are fed from the bottom right side. It's difficult to lift off the bracket at this time since the freon, electric and drain lines are all now running thru the wall. At the most you'd only be able to move it an inch or two or three.

I just posted the above in the event you need to get to the drain line.
Glad all is ok now.
 
  #15  
Old 10-19-13, 05:57 PM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
Thanks. I thought I said earlier... the unit is a Friedman. Yeah, I have a manual, but to see any retaining screw (must be one, the unit hardly budges), I'd have to take the plastic housing off (clips at top). I didn't need to go that far, though.

Fingers crossed.
 
  #16  
Old 10-19-13, 07:01 PM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,221
the unit is a Friedman
Friedman or Friedrich? I don't find anything when I Google Friedman.

I don't like the looks of that cheapy contactor you found. If I was going to go that route, I'd get a name brand definite purpose contactor. It's also possible that if the unit is oversized that it satisfys the thermostat setting before it removes the moisture from the air. How much condensate are you now getting through the drain tube?
 
  #17  
Old 10-19-13, 07:58 PM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
Oops, Friedrich. Sorry.

Condensate? Constant, maybe a drop every 3-4 seconds. Humidity stays between 45-53%, which is perfect for my needs. (I keep guitars in this room).

Unit is definitely oversized. It's the smallest I could find (9.5k btu), in a 180 sq ft room.

The unit does not have a setting where the interior fan stops when temp is reached. It always runs, maybe at the lowest speed (auto), and with the compressor off, but it still runs.

The unit was smelling when temp had been reached. The workaround was to use lowest fan speed, and keep it working as frequently as possible, and then manually (or with contactor) shut the whole system down on reaching temp.

But now that the condensate line is un-pinched, it doesn't smell regardless of whether the unit's cooling, or just running the fan.

The only "problem" I have now is that it ices up when the outside temp falls to 45 deg. Not a big deal, though. Won't be using the unit much longer this season.

If the unit ices, I notice it and shut it off. Why A/C when it's so cool outside? It tends to be a warm room. South facing windows (with awning, though), electronics (computer, huge monitors), tube guitar amp, two warm bodies (me and dog). At this time of year it can drop to the low 40s at night, and still be 68+ in the room. I prefer it around 64-65.
 
  #18  
Old 10-20-13, 06:45 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,221
The only "problem" I have now is that it ices up when the outside temp falls to 45 deg. Not a big deal, though. Won't be using the unit much longer this season.
Most A-C units are not intended to be run when outside temperatures are as low as 45 degrees. If you continue letting the unit ice up you'll drastically shorten the life of the compressor. Low ambient controls are needed to run the unit when it's that cool outside. You might try opening a window when the temperature falls below 60 to 65 outside.
 
  #19  
Old 10-20-13, 08:51 AM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
Are "low ambient controls" something I could add to my set up?

Opening a window seems logical, but is impractical for two reasons. First, the humidity would increase (I haven't measured, but it sure feels more humid when I walk outside at night to let my dog out -- that will change as winter progresses, of course). Dramatically fluctuating humidity is bad for the guitars.

The main reason I can't, is that I have several neighbors that all burn wood constantly as soon as temps drop, and the outside air smells badly of smoke.
 
  #20  
Old 10-20-13, 11:04 AM
CasualJoe's Avatar
Member
Join Date: Jan 2010
Location: USA
Posts: 9,221
Are "low ambient controls" something I could add to my set up?
Probably so, but that wouldn't be a DIY project because they are pressure controls that must be cut into the refrigeration circuit to control the condenser fan. The problem is that with the cendenser fan running when it's cold outside, you are overcooling the condenser coils.
 
  #21  
Old 10-20-13, 11:27 AM
Member
Thread Starter
Join Date: Oct 2013
Posts: 11
Thanks! Not DIY, but now I know what to ask for from a tech.
 
Reply

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread
Display Modes
'