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nednerb 04-02-2012 08:40 PM

Packaged A/C 2 Wire Thermostat Wiring
I recently came across a used Intertherm packaged a/c unit that I have now installed outside my trailer. It has a 2 wire (red, white) thermostat wire. The gentleman who I got it from said to wire the red to the 'Rc' and the white to 'Y' on my thermostat, but I it wont start up. When I picked it up, the gentleman wired it up temporarily in his garage and it kicked right on, so I know it works. It is wired properly to the circuit breaker and is getting power.

I already had central heat which is also 2 wire, but it has no a/c or capability for a/c, so that's why I got the packaged unit. It's ducts connect to the ducts I have for the heat, there's a baffle under the furnace to keep the a/c out. The 2 wire heat works fine with my thermostat, connected to the 'Rh' and 'W'.

I don't have much money, so if I can do this myself I would prefer it. Thanks!

biggles 04-02-2012 08:50 PM

are you connecting the 2 AC red/white wires to the exsisting stat for heat..if you have a jumper between Rc-Rh remove it on the subbase..your working 2 seperate transformers feeding into one stat.all you need to do is wire nut the white and red from the ac together to test it....away from your stat

nednerb 04-02-2012 09:17 PM

I am connecting the 2 ac wires to the existing stat for heat, there is no jumper between the Rc and Rh. I will try wiring the 2 wires together tomorrow afternoon as you suggest to see if it runs...

biggles 04-03-2012 04:45 PM

if you power up the AC just touching the 2-stat wies together it should run. at least the compressor the fan if it is a small unit might run when the compressor runs that why you only have a pair on wires.. for it.

Doc Holliday 04-03-2012 05:26 PM

Can you take pics of the wiring in the stat and in the unit and post them?

nednerb 04-03-2012 05:31 PM

Packaged AC 2 Wire Wiring Update
1 Attachment(s)
Well, looks like the thermostat wiring is not the problem at the moment. Wiring the two thermostat wires to themselves does nothing. As you can see in the attached photo, the yellow wire nut in the lower right hand corner is the two thermostat wires tied together.

I hadn't actually looked under this panel before now, wish I had before I bought it. It did run perfectly at the gentlemen's place before I bought it, he wired the two thermostat wires together too and it started right up and got cold. It did sit through the winter, so I suppose something went wrong then.

As you can see there is some significant water damage to the inside of the control box. Everything has some form of surface rust, the large capacitor to the left having the most surface rust.

Let's eliminate the power source as the problem first. This unit has 10/2 wire back to a 30 amp breaker. The two hot wires from the ac go to the two connections on the breaker and the ground goes to the ground bar. It seemed really straight forward, so if this is wrong please let me know.

Otherwise, it seems I need to replace one or more components in the control box. The contactor switch on the right seems to be in the best shape, though I can see the contacts under the plungers have some corrosion. Like I said, the capacitor on the left is pretty rusty, so perhaps that is the problem, but there is also rust on the transformer, but its not that bad, I figure that isn't the problem. I am not sure what the smaller canister that is in the upper left attached to the back wall is, seems like another capacitor.

Any help would be greatly appreciated!

nednerb 04-03-2012 05:34 PM

I know enough about electricity to be dangerous, if I need to take the components out individually and test them with a meter I can do that....

Doc Holliday 04-03-2012 07:39 PM

Push in the contactor, on the right pole of your single pole contactor, to bring the unit on. If it all works then you'll be back at square one, a control issue and not componentry in the unit.

Be careful when pushing in that contactor. Use a rubber handled screwdriver or rubber handled something.

Doc Holliday 04-03-2012 07:40 PM

And could you please post pics that we don't need a magnifying glass to see? And of all wiring, meaning stat as well.

Doc Holliday 04-03-2012 07:41 PM

And yes, the upside down oval canister is the capacitor for the fan motor. The larger cyclinder shaped, badly rusted one to the far left is the capacitor for the compressor.

nednerb 04-03-2012 07:43 PM

I pushed on it, like you said, though I used a stick, nothing happened. As to the pic, I was just following the rules for attachments. I was surprised at pixel limits for the photos, I will put up a larger version.

Doc Holliday 04-03-2012 07:46 PM

It appears you have a high voltage issue.
Check to make sure you have 240 across both legs. Check each one to ground as well meaning you should have 120-ish volts per leg when checking to ground.

If you have the breaker panel open then check there as well, at the breaker. You should have two indivdual legs of 120-ish and across the two 240-ish.

Bets it's a bad breaker? :laughing: Could be.

nednerb 04-03-2012 07:51 PM

1 Attachment(s)
A larger version of the pic, lets work on this part before we start talking about the thermostat. Thanks again for all your help.

nednerb 04-03-2012 07:55 PM

To be clear, I sat watching it wired like this and the power on for 10 minutes and nothing happened. I pressed the switch in for less than a minute, I realize now I should have perhaps held the switch down longer? I noticed the contacts underneath the little oven mitt shaped pads where the circuit is made are definitely corroded. But I suppose the fact that the solenoid (not sure if thats the right word) didn't draw the switch closed means this corrosion is not the primary problem.

nednerb 04-03-2012 07:58 PM

Doc - I checked that first, there are about 120 volts on each leg at the cut off box attached to the unit, I did not test for the full 240, I was scared already of frying my voltmeter, though I think I shouldn't be, not of voltage, but im not sure. The fact that I did see the 120 volts twice should confirm the breaker is good right? It is a brand new breaker by the way.

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