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Old 08-16-2010, 10:19 PM   #1
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Thermostat wiring


I am trying to get the blower to start before the A/Ccondensing unit as the lights dim when both kick on at the same time in my current rig. I was going to buy a new thermostat but then looked at the manual for mine and it said it would do this at a 5 minute delay but it doesnt. I pulled the thermostat off the wall and found 4 wires hooked up and thought if i went to 5 wires it would make this function work.

My thermostat is a Honeywell older version of CT2800.
Air handler controller is a older version of 50A55-843
My condensing unit is a Fedders C12 series

In the attached diagram the only thing missing was the blue wire so I added it and now nothing kicks on at all, i did remove the jumper off the thermostat between the R and RC(mine is labeled RC not just C) terminal on the T-stat per Honeywell instruction.

Any ideas?

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Old 08-17-2010, 07:12 AM   #2
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Thermostat wiring


Put the jumper back in between R and RC. The 5 minute time delay built into the thermostat is from one cycle to the next, not a one componet comes on before the other operation. Lights dimming on start up means the compressor is having a hard time starting so check the capacitor and maybe need to add a hard start kit such as compressor saver 5-2-1

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Old 08-17-2010, 11:31 PM   #3
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Thermostat wiring


Thankyou Marty S.! Am I understadning correctly that the thermostat compressor protection feature just prevents the compressor from short cycling? I got my (wrong?) idea from another site where somebody claims that a thermostat with cooling droop option enabled will start the compressor 30 seconds before starting the indoor fan, and that this stopped the lights from dimming. But I don't think my t-stat has this droop option.
Link is here:
http://www.homerepairforum.com/forum...n-c-kicks.html

Also did I mention the condensing unit was almost new?
What the heck is the blue 5th wire for?

Thinking if turn the fan on manually first and then the a/c and see if the lights don't dim that a droop option t-stat would fix the problem, but I also did read about the hard start kits and it looks like a good thing to have regardless.
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Old 08-18-2010, 03:54 PM   #4
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Thermostat wiring


I am Dimbulb, not sure why my name has changed here, anyway, So I put it all back to 4 wire and did my test of turning the fan on manually and then starting the AC unit. The lights did dim but less.

I am ready to purchase a hard start cap kit. I see the 5-2-1 is packaged nicely but it is 2x or 3x the cost of supco or mars brands.

How do i size the hard start unit?
The 5-2-1 has 2 versions and the tons ratings overlap:
3.5 - 5 Ton 189-227 MFD Rating Start-Caps
and
4 - 5 Ton 270-324 MFD Rating Start-Caps

My unit is a 4 ton unit pic of original cap is attached to this post

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Old 08-18-2010, 05:09 PM   #5
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Thermostat wiring


Quote:
Originally Posted by jflag View Post
I am Dimbulb, not sure why my name has changed here,
Are you on a different computer ?
Jflag goes back to 2008 as the sign up date
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Old 08-18-2010, 06:19 PM   #6
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Thermostat wiring


Get another capacitor first if you don't have a way to test it. Could be getting weak and they're less then $20. 60+7.5 440 volt.
If the lights still dim buy the good hard start kit, the 5-2-1 even though it's more expensive. I'd use the one for the 4-5 ton on your unit.
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Old 08-18-2010, 11:01 PM   #7
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Thermostat wiring


i would check my power wiring to the panel make shure it was not spiked in with another circut like your lites?it should be on a deticated circut of the rated amps to the power panel and your panel has enough amps to supply the panel loads when on dim lights mean low voltage = high amps
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Old 08-18-2010, 11:34 PM   #8
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Thermostat wiring


jomama -
circuit spec stuff below, what do you think?

Its never tripped a breaker, my svc is 200A, its on a dedicated 40A double pole breaker, connected via 35' run of AWG10CU2G.

Info from condensing unit label:
Fan FLA 2.2
Compressor LRA 137
Compressor RLA 19.7
Max HACR Breaker size 40
Min Circuit Ampacity 28.2

I am not sure of the breaker type, I seem to recall seeing something about the whole HACR breaker type being a BS marketing thing and that they have stopped making them and to just use a regular breaker(I think thats what it is).

Marty - I think I owe you a beer, I am going with the 5-2-1 and will ask about rating at the counter, after scouring the web I couldn't find the answer about the overlap in product specs, the guy on the 5-2-1 tech install video eluded to kits being rated by horsepower but didn' t explain in detail. Ill also check the existing cap.

Scuba - not sure, maybe something weird happened with my PW manager, this is a new computer and I forgot I had been here before

Last edited by dimbulb; 08-18-2010 at 11:52 PM.
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Old 08-19-2010, 04:32 AM   #9
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Thermostat wiring


10-2?

A bit small for your unit.
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Old 08-19-2010, 09:25 AM   #10
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Thermostat wiring


Quote:
Originally Posted by beenthere View Post
10-2?

A bit small for your unit.
Was wondering about that, but why does manufacturer label state: "Min Circuit Ampacity 28.2" ?

10 will do 30 no problem...right? the wire never gets hot or anything
Compressor LRA 137
Compressor RLA 19.7
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Old 08-19-2010, 12:57 PM   #11
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Thermostat wiring


You can buy a time delay relay for the control circuit of the unit which will delay the start and will keep the furnace blower, compressor and fan motors all from starting at the same time. As mentioned above a hard start kit may also help (with the in-rush current and smaller feeder circuit size). Good Luck, let us know how it comes out!
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Old 08-19-2010, 04:35 PM   #12
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How long is the 10-2 wire run.

They list that min. Because that is what the compressor RLA times 1.25% + the fans RLA equals. As per code.

However. they have no idea how long of a wire run the unit will have.
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Old 08-19-2010, 04:58 PM   #13
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Thermostat wiring


Quote:
Originally Posted by beenthere View Post
How long is the 10-2 wire run.

They list that min. Because that is what the compressor RLA times 1.25% + the fans RLA equals. As per code.

However. they have no idea how long of a wire run the unit will have.
Its about 25 -35 foot run between the disconnect box and the main panel.

Am I OK?
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Old 08-19-2010, 05:09 PM   #14
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Length wise its ok.

I still would have ran a 8-2.
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Old 08-19-2010, 07:01 PM   #15
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Thermostat wiring


Quote:
Originally Posted by Superrick View Post
You can buy a time delay relay for the control circuit of the unit which will delay the start and will keep the furnace blower, compressor and fan motors all from starting at the same time. As mentioned above a hard start kit may also help (with the in-rush current and smaller feeder circuit size). Good Luck, let us know how it comes out!
I think they include a time delay relay maybe like this one in the hard start kit:
UMSR-50 Universal Motor Starting Relay



The switch is $12.00 and the Kit is $30.00 and now I am complelty bought in to the saves wear and tear theory so I am going for it. I did manually start the 3/4hp air handler blower and then a minute after the condensing unit (fan and compressor) and the lights still dimmed(seemed to be less but still noticeable) for a bit. The fan motor is 1/4hp. Thinking the Lion here is the compressor.

Hard start kit goes on tomorrow, I watched some net videos that showed Start up Amp draw reductions from 35 -50%.

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