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Author Topic: Air conditioning electrical advice requested please...  (Read 2969 times)
miles2go
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« on: July 16, 2010, 01:53:56 PM »

I have two Dometic (Duotherm) rooftop a/c units. Old ones, circa 1994, model numbers 610015. I only have one touch pad. Here is a picture of the touch pad. It is a touch pad controller with the functions you see listed on the face. It works great. Nice cold air. Both work great, they seem like new. Bought at a government auction and had been on a shelf for years. But I can only control one a/c at a time, by unplugging the touch pad and moving it I can control the other a/c unit, again only one at a time.

I think that someone told me previously one touch pad will not run both a/c units at once no matter how I connect it. I have searched high and low, no other touch pads can I find. Dometic says they were discontinued. These are units before they ran 12v. to the controller, all 110 ac. So in the next post down I will put a pic of what may work if the consensus is right. Sorry you have to read the pic backwards.
« Last Edit: July 16, 2010, 03:18:07 PM by miles2go » Logged
miles2go
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« Reply #1 on: July 16, 2010, 02:06:13 PM »

These are pics of a plain Jane a/c switch salvaged off an even older unit. Well this is the front, below is the important rear for the wires.
« Last Edit: July 16, 2010, 02:37:46 PM by miles2go » Logged
miles2go
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« Reply #2 on: July 16, 2010, 02:40:16 PM »

Ok, here is the rear and my question, wait, I have to show a pic of the controller in the unit first... in the next post...
But while looking at this one note the copper temperature sensing wire, where should this be positioned? I was going to mount this rotary switch away from the unit for easier access. Whatever this is supposed to sense is probably up in the unit right?
« Last Edit: July 16, 2010, 04:16:34 PM by miles2go » Logged
miles2go
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« Reply #3 on: July 16, 2010, 02:53:44 PM »

Ok. If I remove the wires from the controller, up in the left hand corner. The yellow is the medium fan speed, the red is the low fan speed, the black is the high fan speed, and the brown is the compressor. If I attach the wires from the thermostat in the older rotary style switch above, namely the brown to compressor brown, the low fan red to red, the medium fan speed yellow to the tannish center position off of the rotary switch that corresponds to the medium setting, and the high black to black (high), then connect 120v black and neutral to the corresponding wires on the old rotary switch. Will it work? I'll post the wiring schematics next. The ribbon connector in the top right is where the touch pad should connect... but I don't have a touch pad, sigh.
« Last Edit: July 16, 2010, 03:19:32 PM by miles2go » Logged
miles2go
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« Reply #4 on: July 16, 2010, 02:57:33 PM »

Here is the a/c schematic of the units I have.
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miles2go
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« Reply #5 on: July 16, 2010, 02:59:29 PM »

Here is the a/c schematic from the system the old rotary switch came from that I want to use in place of the controller and touch pad. Will doing it this way and bypassing the controller with the older rotary switch fry anything?
« Last Edit: July 16, 2010, 03:13:30 PM by miles2go » Logged
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« Reply #6 on: July 16, 2010, 03:02:05 PM »

I know Sean will have ideas for this one, but my idea would be to make the second unit a slave, delayed, from the first unit. It senses the start of the first unit, and, after a timer circuit, starts number 2.

Shutting down can be done together, but it would be the startup that would be hardest on the available power, whether shore, genset, or inverter.

Those would be my thoughts, and not that difficult to do.

Keith
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miles2go
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« Reply #7 on: July 16, 2010, 03:08:31 PM »

Thanks Keith, but my electrical knowledge is so limited I would not know how to make the second unit a slave. This solution I posted was not my idea, I am not that electrically competent. but I did want to check with all to see if it would work... I am open, very open to better ways to do this. I dislike giving up the touchpad functions, but anything that will work as long as someone advises how.
« Last Edit: July 16, 2010, 04:48:56 PM by miles2go » Logged
RTS/Daytona
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« Reply #8 on: July 16, 2010, 03:24:32 PM »

here's a simple - cheap solution -

add an inexpensive digital thermostat available from walmarts and lowes etc

see--> http://www.klenger.net/RV_General/HVAC_Hunter_Tstat/index.html

pete RTS/Daytona
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miles2go
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« Reply #9 on: July 16, 2010, 03:35:43 PM »

I don't have 12v dc and that solution requires it. I could add a converter to take the 24v and provide 12v, but then all the 110v controls are run by 12v? Is it this simple to just put a Hunter thermostat in there. That link is great. I'll read some more. Thanks. I have three fan speeds, and no 12v, I am not sure the hunter thermostat will work.
« Last Edit: July 16, 2010, 04:45:50 PM by miles2go » Logged
belfert
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« Reply #10 on: July 16, 2010, 04:23:26 PM »

The problem with just adding a regular thermostat to these old Dometics is the Dometic doesn't have the right controls to accept a regular thermostat.  My understanding is the system is completely proprietary.

I see posts in other RV forums all the time from people looking for these obsolete control panels as the A/C won't operate without them.
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James77MCI8
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« Reply #11 on: July 16, 2010, 04:28:17 PM »

What is the control voltage for the key pad?
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miles2go
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« Reply #12 on: July 16, 2010, 04:43:33 PM »

It is 110v. "These are units before they ran 12v. to the controller, all 110 ac." Well, maybe not.
« Last Edit: July 16, 2010, 06:41:31 PM by miles2go » Logged
James77MCI8
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« Reply #13 on: July 16, 2010, 05:01:59 PM »

The schematic says this is low voltage. I don't think the controller is 110. Call me 864-592-2346
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James77MCI8
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« Reply #14 on: July 16, 2010, 05:12:47 PM »

The touch pad is a low voltage interface for the control board. As long as the rotary switches are rated for the current load your scenario should work.
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« Reply #15 on: July 16, 2010, 05:36:02 PM »

A regular household digital thermostat, 24 VAC transformer and some 24VAC relays and you would have a nice control system
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Len Silva
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« Reply #16 on: July 16, 2010, 05:57:45 PM »

I have had some experience with those old style controls and would not recommend them.  I had two on an old Duotherm basement unit.  The problem is that the thermostat carries the compressor load and the thermostat itself heats up, causing the unit to run much colder than you want.  I solved it with some relays.

James has the right idea. A digital household thermostat, a 24 vac transformer and a few relays will fix you up.  If you get a two stage cooling thermostat, you could use it to control both air conditioners, though I would strongly recommend separate thermostats.

Find out what the coil voltage is on the compressor start relay to begin with.

If you decide to go that route, I could help you figure out the wiring.
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« Reply #17 on: July 16, 2010, 06:32:49 PM »

Or, find another controller on ebay.
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miles2go
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« Reply #18 on: July 16, 2010, 06:59:29 PM »

It sounds like it isn't easy but there is a better way than the old rotary controls. Thanks Len for alerting me that the older controls are not the way to go.

James, I think, as Len says, what you propose is the thing to do. Thank you.

Gus, do you mean replace the controller board and the touch pad or "knobs" with another, or just look for another type of touch pad that will work? I have tried that and there are just no touch pads available.

Len, the specs say:
Compressor 12.4 FLA, 63.5 LRA, Min. Circuit Ampacity 20.
Fan 3.10 FLA, 8.5 LRA and 1/4 HP.

I don't know if that has anything to do with the coil voltage of the compressor?
Thanks.
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Len Silva
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« Reply #19 on: July 17, 2010, 06:42:51 AM »

You will have to get right down into the guts of the unit and find the start relay (shown on the schematic)  On the relay itself, it should tell the coil voltage. It might be 120 vac or 12 vdc or something else.  We would need that info to figure out the wiring to replace your controller.
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James77MCI8
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« Reply #20 on: July 17, 2010, 07:35:07 AM »

looks as though the start relay drops the start capacitor out of the circuit once the compressor is up to speed. Can you check the voltage at terminal 5. I'm bet'n it is 110V.
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miles2go
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« Reply #21 on: July 17, 2010, 09:24:43 AM »

I will get into the unit and check the relay for the coil voltage and I will check the voltage at terminal 5. I was out there on top of the bus just now. A new problem surfaced that I will have to fix first. To check the a/c units I had run a direct connection to the panel in the barn/shop and all worked fine. This morning I rewired the connection into what I had hoped would be permanent. It didn't work.

I have a #6 shore cord hooked directly to a 50 amp double pole breaker in the shop panel (240v). The shop panel has grounds and neutrals on the same bus. The shore cord runs through a Marinco inlet to a sub panel on the bus with a 50 amp double pole GFI BREAKER in it. Only one side is used to run to the main panel (120v). At the main panel there is a regular 50 amp double pole breaker that feeds to a 20 amp breaker that feeds the roof air. When I turn the 20 amp breaker that feeds the roof air on the GFI breaker in the sub panel trips off.

The grounds and neutrals are only bonded at the shop panel, no where in the bus are they bonded. I will have to either run an extension cord to run the a/c to check what you need or re-wire without a GFI breaker in the sub panel. I'll go do it now and report back on the voltage you asked me for... unless I do something RADICALLY wrong and then I probably won't report back.
« Last Edit: July 17, 2010, 09:27:10 AM by miles2go » Logged
Len Silva
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« Reply #22 on: July 17, 2010, 10:38:00 AM »

A couple of things;  looking again, I'm sure James is correct, the relay is 110 volts, no need to look at it.

It appears that the neutral is grounded in the AC unit, either intentionally or by accident.  Not uncommon for some very old units to be wired that way.  Shouldn't be hard to find.
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miles2go
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« Reply #23 on: July 17, 2010, 10:40:26 AM »

I disconnected the neutral pigtail from the GFI breaker, hooked the neutral that was into the GFI straight to the neutral bus defeating the GFI functionality and everything worked fine. The voltage reading on terminal #5 was 119v ac as soon as the compressor cut in. So now I have to defeat the neutral to ground in the unit as soon as I find it, then re=attach the GFI functionality. Thanks!
« Last Edit: July 17, 2010, 11:24:15 AM by miles2go » Logged
miles2go
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« Reply #24 on: July 17, 2010, 10:59:54 AM »

I can't find where the ground and neutral are connected, at least not around the control board. The ground wire comes in with the white and black, it's green, and goes straight to a screw on the chassis of the roof unit. I just looked and it can be seen also in the picture i posted of the control board.
« Last Edit: July 17, 2010, 11:04:27 AM by miles2go » Logged
James77MCI8
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« Reply #25 on: July 17, 2010, 01:51:45 PM »

The neut. and grounds are connected through the capacitors. Take a close look at the schematics and you will see it.
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miles2go
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« Reply #26 on: July 17, 2010, 03:24:18 PM »

Ok I see where on top of both capacitors there is a jumper and then it goes to a grounding screw... can I just unplug and remove these? Also the motor is grounded here. Should that be left alone?
« Last Edit: July 17, 2010, 03:41:35 PM by miles2go » Logged
James77MCI8
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« Reply #27 on: July 17, 2010, 04:12:58 PM »

You should be able to disconnect those grounds
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miles2go
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« Reply #28 on: July 17, 2010, 06:26:58 PM »

Thanks James, disconnected the grounds and everything works fine now.
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JLL
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« Reply #29 on: July 18, 2010, 10:25:19 AM »

I also have 2 dometic's that are 1990 vintage.  I Use a pulse  Air.  you can run front and back alternitive  7min. on front then it will switch to 5min. on  the back or you can run both. or front only. It works great if  you have 30 amp only.
JLL
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miles2go
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« Reply #30 on: July 18, 2010, 10:47:58 AM »

JLL,

Thanks for the tip but I googled "Pulse Air" and one of the first things I read was "Not for use with Duo-Therm Penguin touch pad control air conditioners." So that kind of ends that... thanks though.
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