Nest - Rc wire note recognized (code: e73)


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Old 06-01-18, 12:33 PM
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Nest - Rc wire note recognized (code: e73)

I had the Nest for 2 years now...yesterday it saying "Rc wire note recognized"

My A/C wasn't turning on so I went outside and replaced the capacitor and install a hard starter kit. Now I'm getting a "Rc wire note recognized" on my Nest. I looked around for a fuse to see if it was popped but theres none to be found. My furnace looks old... maybe made in 1977.

Anyone have any idea what going on here?

Thanks for any advice.

 

Last edited by SoildSnake; 06-01-18 at 12:44 PM. Reason: missing image
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Old 06-01-18, 02:52 PM
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If you don't have a C wire nest steals power from Y1. You might have disconnected it at the outside unit.
 
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Old 06-01-18, 03:45 PM
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You're going to need a meter to make voltage checks. Check from Y1 to Rc at the stat for 24vac. If it's not there.... check at the control area there from R to C for 24vac.
 
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Old 06-01-18, 03:59 PM
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getting 24 vac at control area at the furnace...get nothing at the thermostat wires
 
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Old 06-01-18, 04:14 PM
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You're getting 24vac on R and C ?
 
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Old 06-01-18, 04:20 PM
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yes I'm getting 24 vac on R and C at the at the furnace wire area.. but getting not thing at the thermostat wires....i also checked outside unit everything seem good, you think its the contactor?
 

Last edited by SoildSnake; 06-01-18 at 04:41 PM.
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Old 06-01-18, 04:43 PM
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Look at my diagram....
The red from the condenser goes to yellow of the stat.
The white from condenser goes to C.
The green from stat goes to G.
The white goes to W.

You need to follow the red wire that goes to the stat. It does not look like it goes directly to R. If it doesn't..... something is interrupting it..... possibly a float switch in the A/c pan or drain.

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The yellow and red wires there with that orange wire nut should be on the Y terminal but that isn't causing this problem.
 
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Old 06-01-18, 04:53 PM
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not the float switch in the A/c pan or drain...that was the 1st thing i checked. All wires are correct.
 
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Old 06-01-18, 04:58 PM
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Look at the 4 wire thermostat cable. I identified white, yellow and green.
Where does the red wire go to in that cable ?
Not R..... correct ?

Your stat needs the R wire to work.

Just to describe the circuit.....
24vac leaves that control on R and goes to Rc on stat. When in cool mode...... 24vac is sent back down the Y1 yellow wire out to the condenser. The C wire from the condenser completes the loop.

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Something in that loop is open.
 
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Old 06-01-18, 05:06 PM
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Old 06-01-18, 05:12 PM
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In every picture..... the red wire is blocked. Just visually check it. Does the red wire from that 4 wire cable go directly to R ?
 
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Old 06-01-18, 05:21 PM
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Yes, the red wire from that 4 wire cable go directly to R.
 
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Old 06-01-18, 05:38 PM
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Ok..... good.

If you go to the nest and take it off the base you should measure 24vac from
R to W
R to G
R to Y.

If you don't measure anything on R to Y. Leave the base off. Go to the furnace..... remove the orange wire nut from the yellow and red splice and just touch those two wires to R. If the A/C condenser doesn't start..... your problem is between there and the condenser.
 
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Old 06-01-18, 06:15 PM
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from the base I'm not getting any thing from
R to W
R to G
R to Y.


okay I took off the orange nut from the yellow and red splice and touched those two wires to R. Nothing came on.
 
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Old 06-01-18, 08:28 PM
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We're sort of going around in circles here.
IF.... you measure 24vac from R to C at the control board.
And IF the 4 thermostat wires are connected.... there would have to be voltage at the stat.

Try a jumper from R to W at the board. That should start the furnace.
Try a jumper from R to G at the board. That should start the blower.
 
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Old 06-01-18, 09:09 PM
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okay i tested again from the thermostat this is what I'm getting.

R to W 12.20 vac
R to G - 24 vac
R to Y. - 1.084 vac

Nest thermostat is still blank...no power
 
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Old 06-02-18, 08:10 AM
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Still pointing to Y being the problem or the connection between C at the furnace and C at your outside a/c condenser's contactor. Check the connections to the contactor. Or remote possibilty of an open contactor (measure ohms across terminals to be sure).
 
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Old 06-02-18, 08:20 AM
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Yes... definitely.
The voltages measured at W and G are ok.
You've previously touched the yellow wire to R at the board with no response.

The two wire cable that goes out to the condenser is in question.
Also the contactor and a possible low pressure switch.
You could be low on refrigerant. That would keep the line open.
 
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Old 06-02-18, 08:56 AM
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I'm getting 24vac from Red wire from the thermostat.....would a bad compressor be the cause of the issue?
I hold down the bar from the contactor from the outside unit ...ONLY the FAN is coming on but not the compressor.
 
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Old 06-02-18, 09:18 AM
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No.... a bad compressor won't cause the problem but the fact that the compressor and fan aren't coming on together is a problem.
 
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Old 06-02-18, 09:30 AM
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I'm getting 24vac from the Rc wire... I'm not sure why I'm getting the e73 code .
 
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Old 06-02-18, 10:17 AM
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You need a complete loop for the nest to work. You do NOT have a complete loop.
Your nest needs to steal power from the circuit to charge.

Look at the diagram. R is 24vac and C is technically 24vac - or ground.
Think of R as positive and C as negative. The nest needs both to charge. It gets its "positive from the R connection. It gets its "negative" thru the contactor and the lo pressure switch inside the condenser. You have something open in the outside condenser line. As long as that circuit is open.... the nest will not function.

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Old 06-02-18, 10:56 AM
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you're corrected there was a loose wire on the outside contactor that's why the Nest wasn't working. So that part is now fixed.

NOW back to my 1st issue with the compressor not coming on.

Note: I also installed a hard starter for the compressors.

I tested and power is coming from the compressor but its not coming on for some reason.

 

Last edited by SoildSnake; 06-02-18 at 11:24 AM.
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Old 06-02-18, 11:50 AM
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I would put on a pair of safety glasses and carefully remove the cover from the compressor wiring access. That location is a weak link in the compressor and can blow out if compromised.

First look for loose burned wires. If they look ok you'll need an ohmmeter to check the compressor windings.
 
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Old 06-02-18, 01:24 PM
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where do i find what type of freon do it use?
 
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Old 06-02-18, 01:30 PM
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It's R22. Why do you need that ?
 
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Old 06-02-18, 01:38 PM
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looks like i need to replace the compressor
 
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Old 06-02-18, 01:49 PM
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Ok. Just so you know.... we can't help you with that in the public forums.
Only an EPA licensed tech can handle R22 products.
 
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Old 06-02-18, 01:54 PM
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okay so i removed the cover from the compressor and this is what i found...can this be fixed?

 

Last edited by SoildSnake; 06-02-18 at 02:43 PM.
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Old 06-02-18, 02:56 PM
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I think i found the issue with why the compressor is not working.
 
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Old 06-02-18, 03:58 PM
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Depends on if the terminals are burned off the compressor or not.
 
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Old 06-02-18, 04:32 PM
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FIXED, house is now nice and cold! Thanks everyone for your help and advice.
 
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Old 06-02-18, 06:18 PM
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You're welcome.

Make sure all three of those connections are clean and tight so you don't have a repeat.
 
 

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