# A/C unit outside not coming on



## gregzoll (Dec 25, 2006)

Broken wire from the air handler to the outside condenser, tripped breaker, fuse disconnect outside corroded, or missing, corroded connections in the outside unit, blown fuse, or broken connection in the air handler. Those would be the best places to start.


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## Doc Holliday (Mar 12, 2011)

Wait, the title of the thread says that only the outside unit won't come on. When you put the stat in the auto and cool mode and drop the set point (desired temp) really low (to make certain the system is calling to come one) what happens? Is the inside blower coming on at all or not?


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## Ksjka (Mar 19, 2011)

Doc Holliday said:


> Wait, the title of the thread says that only the outside unit won't come on. When you put the stat in the auto and cool mode and drop the set point (desired temp) really low (to make certain the system is calling to come one) what happens? Is the inside blower coming on at all or not?


No. The inside blower doesn't come on if set to auto no matter what it's set at. It will come on if I switch it from auto to on though. It's night time so I haven't been able to check anything outside. The breaker isn't tripped though.


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## gregzoll (Dec 25, 2006)

If it comes on when set to Fan, then call a reputable HVAC tech. Worst case scenario being that it is a weekend, it will cost you triple.


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## mastertech (Mar 14, 2011)

from reading the post that was made whats different going on here!did it ever run right ,or did you just move there or how about this,did you just try to put a new thermostat on the system? The sequence of operation is like this: On the t-stat auto-on switch all that does is control your indoor blower motor.In the on position the blower motor will run 24 hrs a day.When the auto position is selected the blower motor will cycle off when the home reaches the desired temp thats selected. If the system wasnt giving you any problems before and nothing new has been done to it ,the outdoor unit still giving you a problem. When you select the desired temp you want, first thing youll notice is the inddor blower coming on.This will tell you the tstat is telling the system to go to work. If the outdoor unit isnt working the most common thing to do first is check the breaker at the main panel,if its on go ahead and reset it . No od unit still ,than ck the fuses in the dissconect,if fuses are good and you have power from the breaker,well you have a control problem with the low voltage going to the od unit.Now on one of your posts the fan doesnt come on in auto no matter what you set it on .but comes on when on is selected. That statement right there tells me the t-stat is defective due to not coming on in auto.since it comes on in the on position that tells me that the relays are ok.as a logical guess the t-stat might be your only problem.


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## COLDIRON (Mar 15, 2009)

Do you have 24 volts outside when you turn the thermostat down with it in auto and cool. If not post back if so post back again and someone will walk you through it.


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## Doc Holliday (Mar 12, 2011)

To check to see if stat is bad: turn breakers off for both furnace and a/c unit (outside unit). You will need a small screwdriver to disconnect the red wire on the "R" terminal, the green wire from the "G' teminal and the either blue or yellow wire from the "Y" terminal at the thermstat. Twist all three of those wires together making certain they do not touch anything else whatsoever, and turn the breakers to both units back on. 

r is 24 volts so power, g is for the fan and whichever wire is on the Y terminal, either blue or yellow, is cool (outside unit) so now all you've done is take away the switch (stat) and manually tell your system to go to cool. If it works, your stat is bad. 

It is important to not let those wires touch anything and to shut off system by the breakers before you mess with any wires and then shut the system down by the breakers after youv'e twisted those wires together to check if system comes on (after turning breakers back on) or you stand a chance of blowing the fuse in the furnace.

Hope that helps. If nothing works this way you might be looking at a control board but this would be a good place to begin diagnostics as stats go bad regularly.


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## Hubcap626 (Feb 12, 2011)

Usually stats are the last thing to go bad, if it's in auto it won't come on until the cooling makes at the condensing unit. Low pressure switch open? Fuse blown? You will need a meter and check whats going on.


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## Doc Holliday (Mar 12, 2011)

gregzoll said:


> If it comes on when set to Fan, then call a reputable HVAC tech. Worst case scenario being that it is a weekend, it will cost you triple.


 
We don't charge any different for the weekends. Nights and odd hours, yes. Weekends, normal rate.


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## mastertech (Mar 14, 2011)

Ok I was thinking about a residential application and not a commercial tstat.On a residential stat the auto modes for the blower only.It has nothing to do with the outside unit coming on.The blower will come on as soon as theres a call for cooling.This post says Im a newbie to this site,far cry from a newbie in the field>Not a Know-it-all but not an green horn either.Its not my first rodeo !


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## Doc Holliday (Mar 12, 2011)

1mastertech said:


> Ok I was thinking about a residential application and not a commercial tstat.On a residential stat the auto modes for the blower only.It has nothing to do with the outside unit coming on.The blower will come on as soon as theres a call for cooling.This post says Im a newbie to this site,far cry from a newbie in the field>Not a Know-it-all but not an green horn either.Its not my first rodeo !


 
All stats have everthing to do with the a/c unit coming on. Auto and cool. They have no idea where they are being installed, commercial or resi, and for the most and simplist part are the same.


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## Doc Holliday (Mar 12, 2011)

And let's not forget than many regular split systems (and a few package units) you'd find in homes are installled in light commercial. e.i, offices.

I can take my stat from my house and walk down the street to the commercial business park, remove their stat and put mine on and the system will work. Split or package any size. I can take their stat and install it in my place just as easily.

I'd have to make sure the stats were set for either electric or gas if applicable but that's about as far as that goes.


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## Doc Holliday (Mar 12, 2011)

All a stat is is a switch, nothing much more than that. Controlled by low voltage. By turning a stat to "on" or to "auto" and "cool" or to "auto" and "heat" or simpy "off" you tell the stat where you want that low voltage to go or not go.


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## mastertech (Mar 14, 2011)

I agree but the execution of a low voltage command is being looked at differently and there is a difference.On a stat the auto on featutre controls the blower only and has nothing to dowith the outdoor ac.Theres a stat that has a auto feature that wikll run the heating and cooling so a customer doesnt have to manually change modes to get the system to heat or cool.Its called an auto changeover tstat.Im confident that we know whats going on but are looking at it at different applications.If I cant work a stat aftyer 30 yrs in this trade well ill hang my tools up!


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## Doc Holliday (Mar 12, 2011)

1mastertech said:


> I agree but the execution of a low voltage command is being looked at differently and there is a difference.On a stat the auto on featutre controls the blower only and has nothing to dowith the outdoor ac.Theres a stat that has a auto feature that wikll run the heating and cooling so a customer doesnt have to manually change modes to get the system to heat or cool.Its called an auto changeover tstat.Im confident that we know whats going on but are looking at it at different applications.If I cant work a stat aftyer 30 yrs in this trade well ill hang my tools up!


 
I think I might be misunderstanding but here goes nothing...

The stat on auto cool is now a thermometer used when above desired set point to close a circuit, the cooling circuit, thus telling the a/c unit to come on simultaneously with the blower. The same for heat and auto, thermometer/air temperature sensor switch telling the heat to kick in with the blower if temperature is below desired set point.

On "on" all it's doing is telling the blower to come on by itself, no heat or cool.

What am I missing?


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## Doc Holliday (Mar 12, 2011)

When that cooling circuit is energized than the 24 volts is energizing the coil at the contactor in the condenser and pulling in the contactor (again,at the a/c unit/condenser) allowing the high voltage to pass through to turn on the condensing unit, all because of the auto and cool setting being on and sensing the temperature and closing the low voltage circuit to the condensing unit and around and around we go. 

What am I missing? I'm not understanding this auto stat you are talking about..?


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## COLDIRON (Mar 15, 2009)

Sounds like you people scared away Ksjka with all your theory.


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## Doc Holliday (Mar 12, 2011)

COLDIRON said:


> Sounds like you people scared away Ksjka with all your theory.


See thread "HVAC is not a DIY event."


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## COLDIRON (Mar 15, 2009)

Doc could you please cure me I can't understand why you pointed me to the other post. This guy is having a problem and this is a DIY site why does everyone try to turn it into a HVAC PRO site?

It's nice to have the Pro's(like me) and you to help.

Most of these people ask legitimate questions to the best of their limited knowledge, strange yes at times but they do need help.

I do remember when I was young struggling so called mechanic trying too feed my family and learning. I remember those days and never forgot. 

The only thing we can do is try to steer them in the right direction if they don't go that way OH well that's on them.
Later Doctor of Air.


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## Doc Holliday (Mar 12, 2011)

COLDIRON said:


> Doc could you please cure me I can't understand why you pointed me to the other post. This guy is having a problem and this is a DIY site why does everyone try to turn it into a HVAC PRO site?
> 
> It's nice to have the Pro's(like me) and you to help.
> 
> ...


 
*Meow!!* I was just messing around. You said he got scared and hvac being a little more precise than what many give it credit for, I said that. 

Of course I'll help anyone out and like to do so and not only for their benefit but mine too as talking assorted problems out keeps me sharp, keeps me thinking.


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## COLDIRON (Mar 15, 2009)

doc holliday said:


> *meow!!* i was just messing around. You said he got scared and hvac being a little more precise than what many give it credit for, i said that.
> 
> Of course i'll help anyone out and like to do so and not only for their benefit but mine too as talking assorted problems out keeps me sharp, keeps me thinking.


" what's this meow crap ? "


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## Doc Holliday (Mar 12, 2011)

COLDIRON said:


> " what's this meow crap ? "


 
:laughing: just messin' around, friend. 

http://www.youtube.com/watch?v=5GEd0_PviyM


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## COLDIRON (Mar 15, 2009)

Doc Holiday said:


> :laughing: just messin' around, friend.
> 
> http://www.youtube.com/watch?v=5GEd0_PviyM


" I thought this was the DIY site not the Comedy site"


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