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Old 05-24-2012, 07:39 PM   #1
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AC Stopped working after condenser was moved


Hello,

I am an electrician, and am familliar with motor control, but I was hoping to get a little help troubleshooting what I think will be routine for someone familiar with HVAC.

My friend had an addition put on his trailer and the contractor moved the condensing unit, it has not worked since.

I do NOT know if he disconnected the control circuit to move it, but I have the suspicion that he may have miss-wired it if he did.

When I press the relay in manually the unit starts up with no problems, so the High voltage is correct and the unit does not appear to have a mechanical problem.

I took a picture of the thermistat side wiring (this unit is dedicated to AC, there is a seperate stat for the furnace)


Here is the wiring on the unit side. The Red / White / Blue / wires enter from the bottom left:


The Red wire takes one side of the 24v to the thermostat.
The Blue wire goes to what I think is a timer unit (solid state) below.
The White wire connects to the green that goes to the 'contacor?' above. (I am thinking this is an intermittent relay between the low voltage and the high voltage relay . . .? )

Here is what I could make out of the Schematic on the cover (sorry, it was pretty worn)


Here is the Model #


The only doccumentation I was able to come up with was a manual (with no electrical schematic )
I will include a link: here

I measured 24v from the secondary of the transformer, but I cannot remember the voltage I read between the red and other 2 conductors ( I want to say ~24v but I can't quite remember) [it's not 0v]

I can get these readings when I go back, but I was hoping to have a few tips to try when I make the trip.

Also, does this unit contain the forced air fan for the duct work?

Thank You for any tips you can give, let me know if I left anything out!

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Old 05-24-2012, 09:07 PM   #2
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AC Stopped working after condenser was moved


When T-stat calls for AC, it send 24V to the relay (the one has a button which you can push to start the system). the relay will pull the button in to start the system. If the 24V is there, but the relay's button is not pulled in, replace relay. if 24V is not there, then something wrong with your T-stat or transformer. The condenser has nothing to do with in house air. There is another blower circulate the air inside the duct.

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Old 05-24-2012, 10:31 PM   #3
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AC Stopped working after condenser was moved


blue and white wires need switched. Does the blower work? If no, then check for 24V at the transformer.
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Old 05-25-2012, 01:01 AM   #4
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AC Stopped working after condenser was moved


Quote:
Originally Posted by clocert View Post
When T-stat calls for AC, it send 24V to the relay (the one has a button which you can push to start the system). the relay will pull the button in to start the system. If the 24V is there, but the relay's button is not pulled in, replace relay. if 24V is not there, then something wrong with your T-stat or transformer. The condenser has nothing to do with in house air. There is another blower circulate the air inside the duct.
Thanks clocert,
Since the Green wire goes to that black module before the relay, can you tell me what that black module is? (I am curious)

I can assure you that there is 24v on the transformer, and it returns from the T-stat

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Originally Posted by hvactech126 View Post
blue and white wires need switched. Does the blower work? If no, then check for 24V at the transformer.
Thanks hvactech,
I was thinking about swapping those myself, but just worried that I would short something out since I didn't know what I was doing.

I will try switching those wires.
Can you tell me why there are 2 wires returning from the T-stat?
I would assume that one controls the AC and the other the Blower (since this can be controlled from the T-stat)

If this is the case, then why do I not see any control or other wire exiting the Unit? (only the 240 and 3 conductor control enter the unit)??
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Old 05-25-2012, 01:23 AM   #5
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AC Stopped working after condenser was moved


I believe that black module is your time delay. You need to check if the 24V is at the relay or not. (the 2 small wires from T-stat should have 24V)
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Old 05-25-2012, 07:07 AM   #6
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AC Stopped working after condenser was moved


Blue wire from stat is currently connected to yellow which goes to a 5 min time delay module.
White wire from stat is currently connected to green which goes to the blower relay.
The stat terminal designations are:
R - 24V hot
Y - compressor control
G - Blower control
W - heat control

Switch the wires and then test operation. If you still do not get anything then test for voltage to and from the transformer.
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Old 05-25-2012, 08:26 AM   #7
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AC Stopped working after condenser was moved


Quote:
Originally Posted by hvactech126 View Post
Blue wire from stat is currently connected to yellow which goes to a 5 min time delay module.
White wire from stat is currently connected to green which goes to the blower relay.
The stat terminal designations are:
R - 24V hot
Y - compressor control
G - Blower control
W - heat control
Thank You hvactech, this explanation makes perfect sense to me
I am hoping to get over there later today to try this out.

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Originally Posted by hvactech126 View Post
Switch the wires and then test operation. If you still do not get anything then test for voltage to and from the transformer.
So . . . here is a thought:

If the blower and compressor control are in fact swapped, . . . then if I were to turn on both so that the stat was calling for blower & compressor, shouldn't the system then run . . . ?

(I confess, I never tried the blower control from the T-stat)
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Old 05-25-2012, 09:07 AM   #8
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AC Stopped working after condenser was moved


Yes they should run the way it is set up the even though the wiring is currently wrong. That is why you need to verify 24v with a meter. Normally when a stat calls for cooling it also calls for blower. You can wire nut all 3 wires together and verify if stat is good or if you have no 24v or possible broken wires.

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Last edited by hvactech126; 05-25-2012 at 09:10 AM.
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