Heat but no A/C


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Old 06-01-08, 10:41 PM
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Heat but no A/C

Folks- this cannot be that complicated. I have separate heating (gas fired boiler w/ hot water) and cooling (Carrier central A/C). The thermostat has 4 wires:
Red to RT on heating system relay- calls for heat, boiler fires & pump kicks on.
White to WT on heating system relay.
Green- Goes to A/C air handler terminal.
Yellow- Goes to A/C air handler terminal which also has red wire going outside to condensor.

From the other air handler terminals I have:
Common terminal- Gray wire outside to condensor, White going ?, and Orange going ?. Back of this terminal connects to transformer inside air handler.
Red terminal- Red going ?. Back of this terminal goes to transformer inside air handler.

I need to know where the Red & White wires that are going ? , just hanging loose are supposed to go. I believe they were tied into a separate Type 91 relay before I accidentally pulled them loose repairing my heat.

Please HELP- house is HOT even at night!
 
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Old 06-02-08, 01:56 AM
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Air Conditioning Repair

Not enough info on possible use of relay but if you have 24v available to you on the yellow wire coming from your thermostat you need to get that 24v signal out to your condensing unit to energize and close the contactor they may have used the relay because you have 2 transformers so all I guess for you to do is put those two wires you don't have a home for on the normally open terminals on your 91 relay otherwise like I said if you have 24v on the Y terminal of your thermostat and you can get it to your outside unit on the two wires going outside you will have cooling
 
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Old 06-02-08, 07:33 PM
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No A/C

Mike: Thanks for the response. I checked the thermostat and I saw that the yellow wire was not making good contact with terminal. Tightened it up, and the air handler blower kicked on. However, the outside condensor did not turn on. Checked voltage at thermostat & read 24VAC+. Took a break for dinner, rechecked voltage at thermostat, and both green & yellow terminals now only reading 19.8 VAC. Same 19.8 reading for both wires coming from transformer, and consequently, same for terminals of air handler "control panel". Also, I am getting no juice to air handler unless I hook up the red wire that was hanging loose, as mentioned before, to the RT terminal on my HEAT relay. How can I fix this mess, anybody??
 

Last edited by bdajewel; 06-02-08 at 07:43 PM. Reason: Clarification
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Old 06-02-08, 11:18 PM
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Anybody?

Where are the A/C experts, semi-experts, moderators, ANYBODY?
 
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Old 06-03-08, 08:45 AM
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HEat but no ac

3 days ago I replaced a furnace and condenser and wire it up. after completion, I started up and when on heat mode everything works great but with the stat on auto and on calling for cooling, nothing happens, no fan and no condenser come on. I check the wiring several times and everything checks out fine. I jumped the g wire to the R wire and the fan comes on but the condenser also comes on with it. that got me very confused so I recheck my wiring again and every connection is where its supposed to be right now i have a Gibson split system with condenser outside very basic connections to the stat-board- and condenser. if I switch the fan from auto to on it will run. I don't understand why it wont run on auto and why when I jumped g to R both the outside unit and indoor unit comes on. help please really need it .. thanks
 
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Old 06-03-08, 08:48 AM
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3 days ago I replaced a furnace and condenser and wire it up. after completion, I started up and when on heat mode everything works great but with the stat on auto and on calling for cooling, nothing happens, no fan and no condenser come on. I check the wiring several times and everything checks out fine. I jumped the g wire to the R wire and the fan comes on but the condenser also comes on with it. that got me very confused so I recheck my wiring again and every connection is where its supposed to be right now i have a Gibson split system with condenser outside very basic connections to the stat-board- and condenser. if I switch the fan from auto to on it will run. I don't understand why it wont run on auto and why when I jumped g to R both the outside unit and indoor unit comes on. help please really need it .. thanks
 
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Old 06-03-08, 08:58 AM
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You replaced the outdoor (condensing) unit yourself?
 
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Old 06-03-08, 09:13 AM
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yes, I actually work in commercial buildings but had never replace an hole house split system before. first experience
 
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Old 06-03-08, 09:25 AM
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Heat works But AC doesnt.

yes, I actually work in commercial buildings but had never replace an hole house split system before. first experience
Edit/Delete Message. I'm good with the mechanicals and I understand some wiring and right now I don' know if I have a bad board or a bad connection somewhere. I wired it the following way: R, G, Y W from stat To same terminals on the board and them Y and C terminals from the board to the condenser outside Y to the Yellow wire on the contactor and C to the black wire on the contactor at the outside unit.
 
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Old 06-03-08, 09:45 AM
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Is not the wiring that concerns me but the mechanical side of replacing an A.C. system. You need a vacuum pump, a micron-gauge, a nitrogen cylinder with regulators, gauges, a B-tank + brazing rods, a new filter dryer; spare refrigerant for topping-off a charge if needed would not be a bad idea either. A superheat or subcooling charging chart. There must be compatibility (SEERs, Refrigerant type - flushing of old lines if it's a new refrigerant, or better, a complete line changeover)

If the changeover is not done following standard replacement procedures (a good evacuation is a must!), there you have it, a likely not cooling scenario.
Get my point?
You may indeed work in commercial buildings...but...in the refrigeration side? or in the general building maintenance side? This type of work is not like changing a motor or adding a breaker, or replacing a lighting fixture...you need specialized training in HVAC/R.

And most importantly, having an EPA certification is a must have by Federal law.
 
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Old 06-03-08, 11:37 AM
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Heat, no a/c

Just my luck: I ask for help, and get my original question answered by another question which has nothing to do with my situation. I SURRENDER! Will just have to bite the bullet and pay for someone to make a service call and hook up a couple of wires.
 
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Old 06-03-08, 11:44 AM
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Angry Heat, no A/C

Bomdy: Thanks for your post- maybe somebody can help us both, but it doesn't look very promising to me so far.
 
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Old 06-03-08, 01:29 PM
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Maybe I didn't explain myself well, I have and used most of the equipment u mentioned above. and took all the precautions neccesary to make a nice and clean install and have no mechanical issues. Away from that, the only existing piece of equipment there was the furnace, the Ac condenser part is all new istallation including new lines and new evap. coil. leak check it with nitrogen and had the lines vaccum to 500 microns. had a good 40 degree low side temp after done toping it up. had to jumped to make it run while toping it up and checking pressures but everything mechanical check out fine. Anyways if any one could help me with my question out there going back to the subject it will be much appreciated if any one could help me with this.
 
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Old 06-03-08, 02:53 PM
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pls post the MFR and M/N of both, the condensing unit as well as the furnace. Ditto for the thermostat.
 
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Old 06-04-08, 04:46 AM
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Both the condensing unit and furnace are Gibson made by nordyne and the tstat is a honeywell, don't remember the model number right now but it ends in 110
 
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Old 06-04-08, 09:30 PM
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Getting closer

OK, I think I am getting closer. I replaced thermostat, and am getting 26.5VAC from Red terminal on A/C air handler control panel to the Common terminal, and to the green terminal, and blower fan is running fine. However, I am not getting any reading from Red to Yellow (which means no condensor fan running outside). I looked behind control panel, and noticed that all but the yellow terminal had wires connected both in front & in back. Is this the problem? I have not switched or removed any contacts on either the front or back of control panel since unit was installed 26 years ago (Carrier A/C only central unit). In other words, I have yellow going straight from thermostat Y terminal to control panel Y terminal, but no other connection to it.
Incidentally, I believe the other relay I have is for a time delay on the blower fan after condensor fan cuts off. However, I am leaving that out of the equation right now. PLEASE HELP as it hit 98 deg. today & hasn't cooled off much tonight.
 
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Old 06-05-08, 03:17 AM
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Air Conditioning Repair

Sorry I can't respond very quickly but it's hot outside and I can't fix anything sitting in front of this computer the control panel you speak of is it on the air handler if so the wire coming from your Y terminal on your stat needs to go continuously through to the contactor in your outdoor unit passing through any safety devices that may be in the system then a second wire needs to go from the common side of the control transformer to the other side of the coil on the contactor in your outdoor unit if you have no voltage reading between R and Y but you have 24v between R and common that means your thermostat is calling for cooling so the problems is downstream from there electricity is like water it is taking the path of least resistance if you take readings on both sides of a closed switch the power is going right by you if you got 24v between R and Y that would mean the switch is open and the power would then want to flow through your meter leads if you want to know were you voltage is and isn't you should have one lead on the common side and use your other lead on R or Y or anywhere else in the circuit you are trying to discern the presence of control voltage
 
 

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