RTH8580WF - not sure if this is T'stat behavior or bad a/c


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Old 06-29-14, 06:04 PM
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RTH8580WF - not sure if this is T'stat behavior or bad a/c

Note: I replaced the G wire for C (C is required) as I only have 4 wires going through the wall. Instructions says that if you do that, the only thing you give up is the option to run the FAN manually. I am fine with that.

Anyways, when I first turn the a/c on the compressor kicks in and everything is fine and dandy. When set temp. is reached, compressor shuts down and the system fan runs for another 2 minutes or so and then it shuts down waiting for the temp. to rise before it calls for cooling again. Normal, right?

Few minutes later - can't tell you how long, perhaps 5 or 10 - the system fan, as well as the condenser motor fan turn on, but not the compressor. They can run for quite some time...I measured 20 minutes today, before the compressor kicks in again.

I thought something was wrong with the a/c unit. My a/c guy immediately mentioned that it could be a bad capacitor. He stopped by the next day and ruled that it is definitely a bad capacitor and replaced it.
Today was the first day we had to use the a/c after the capacitor was replaced and I noticed that the a/c behaves the same way again.

When the compressor is on, the unit cools the house and everything is good. But I never had this behavior with my older (non Honyewell) T'Stat, so I am not sure what's going on. Why would the condenser fan comes on, along with the indoor unit fan, without the compressor and stay on for ~20 minutes before the compressor kicks in?
Also, isn't the fact that I don't have a G wire any more means that the fan won't work without the compressor?

Thanks for your help.
 
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Old 06-29-14, 06:32 PM
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Do you have a heat pump system there ?
 
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Old 06-30-14, 04:24 AM
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No heat pump and it is set up as '1' (standard heating/cooling system).
 
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Old 06-30-14, 09:30 AM
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This is an intersting problem. How did you "replace the G wire for C"?
 
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Old 06-30-14, 09:48 AM
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With some system you have to power the Y and G both to get the A/C to run correctly. If you power just the G terminal only the fan runs.

Your unit has a delayed fan control that seems to work with just the Y terminal.

Can you post the make and model of the air handler.
 
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Old 06-30-14, 09:52 AM
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Just as the Honeywell instructions says. I don't have a G wire any more (in the T'stat), instead I use C.
 
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Old 06-30-14, 10:09 AM
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If the condenser fan motor runs but the compressor does not it points away from the stat.

The compressor terminals should be inspected, the wiring to the new cap should be rechecked and the starting amperage of the compressor should be checked.

You may need a hard start kit.

Is the compressor timer setting on the stat at 5 minutes?
 
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Old 06-30-14, 02:27 PM
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OK, here goes:

The a/c unit is a Goodman (if it matters; 1st attachment).
The air handler is a Bryant Plus 80
Second attachment is current wiring inside the air handler.
Third attachment is the wiring connection between handler, T'Stat and condenser. The brown wire on the left is going to the T'Stat (4 wires); the middle one that goes down is going to the handler; the one on the right (only 2 wires) is going to the condenser. As you can see, there is an unused wire (green) in the air handler.

Fourth one is the T'Stat wiring.

I spoke with my HVAC guy who will be here tomorrow, he mentioned hard start as you did, Houston204. Not sure what it is, but when the fans are on (no compressor) I do hear some kind of a motor/pump that kicks in for about a second every 3-4 minutes or so. I can also feel it through the floor. I thought it was the condensate pump or even my sump pump, but both are empty so it's definitely not a pump. Could this be it, trying to start the compressor?

Thanks again!

P.s. - I don't think the T'Stat has a specific setting for the compressor.
 
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Last edited by SBI; 06-30-14 at 04:52 PM.
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Old 06-30-14, 05:40 PM
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Is there a wiring Dia. Of the condenser unit ? Post a pic if there is.When you hear the thumping can you tell if the compressor Contactor is jumping in and out?
Geo
 
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Old 06-30-14, 05:42 PM
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I would also like to see a pic of the capacitor. It could be incorrectly wired.
I'd expect red and purple on Common, yellow on Herm and brown on Fan.
 
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Old 06-30-14, 08:27 PM
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OK, will have to do this tomorrow during daylight.

I could not hear any contactor jumping, but I am almost certain that it's the compressor trying to start for several minutes/few attempts until it finally kicks in.
 
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Old 07-01-14, 05:20 AM
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Here are the wiring diagram and pictures of the capacitor. As far as I can tell, the capacitor seems to be wired correctly.
 
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Old 07-01-14, 05:28 AM
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Here is a cropped/higher resolution of the diagram.
 
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Old 07-01-14, 11:22 AM
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Update: My HVAC guy stopped buy, added a hard start kit and so far it works fine. Will update if anything develops. Thank you all!
 
 

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