Ac comes on for a second then off then on


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Old 05-02-14, 05:11 PM
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Ac comes on for a second then off then on

Just recently had freon added, changed contractor, tstat wire to the outside, and tstat to fix a no ac condition. It has been working great but now when ac or heater is turned on either will come on just for about 30 or 40 seconds the go off then attempt to start again after about 20 seconds. It will attempt to come on about 3 times then will come on for about 30 or 40 seconds then start the whole process over again. As the previous issue was outside this one seems to be inside. Any help would be GREATLY appreciated. Thanks in advance.
 
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Old 05-02-14, 06:15 PM
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That doesn't make any sense so we'll need to start at the beginning.

What is the make and model of your furnace ?

I think I remember from your other thread that you have a voltmeter. I would located the control board in the furnace. It's usually in the blower cabinet below. When you open the cabinet a safety switch turns off all power. You'll need to hold that in or temporarily tape it so that it stays in.

At the control board.....
R and C is the 24vac.... see if that stays stable.
Y and C is 24vac when A/C is on...... is that stable.
W and C is 24vac when heat is on..... is that stable.

We need to find out exactly what is losing power.

As an added thought..... does your thermostat run on batteries... they may need a replacement.
 
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Old 05-03-14, 05:19 PM
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ok--it's a 94 Bryant ac unit and an 02 furnace (not sure what type)-4ton. Yep--it has the switch that shuts off power when panel is taken off. So for the above--I need to check the tstat wires in the cabinet correct? Yes my tstat runs on batteries but they are new--did just install the tstat--so maybe I have a had one as well? I will check the above and get back--thanks again!!
 
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Old 05-05-14, 03:29 PM
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Ok--I have 24v to the tstat wires inside the unit in the house. I also turned the ac on just for grins (set to 71 and inside temp was 79) AC ran as normal until inside temp dropped 2 degrees then would cut off attempt to come on twice then come on as normal. Also I checked outside and although the blower is doing this on off thing the fan outside would continue to run and blower hot air as it should.
I am suspecting something on the control board? Also with the tstat off and blower on--it works as it should as well.
 
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Old 05-05-14, 03:39 PM
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AC ran as normal until inside temp dropped 2 degrees then would cut off attempt to come on twice then come on as normal.
Ok... from what you are telling us you have an inside blower issue. If you put the thermostat in FAN ON mode is everything working normally ?

If you only have problems with the fan in AUTO FAN mode then check C and G for 24vac at the furnace. See what that voltage does. If you lose it... it would point to a t'stat problem.
 
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Old 05-05-14, 03:56 PM
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correct--tstat in fan on mode--blower works as normal. On auto if there is a big split in tstat temp and actual inside temp it will run until 2 degree drop then do the start stop thing. I will check c and g
specifically for the 24v. Will let you know the outcome. Thanks again.
 
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Old 05-05-14, 05:24 PM
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That almost sounds like the G wire is not connected to G at the thermostat. When thermostats are set up for back up heat..... they change/energize different terminals when certain temperature splits occur.
 
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Old 05-06-14, 05:45 PM
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Found the problem. Checked the c and G and all the others again--all was fine.
I checked the capacitor just for grins and it was good. I thought while I was in there I would feel the blower motor--well--it was very hot--that's the problem--that thing is getting hot which is opening the thermister (or whatever it's called) which is why it will run after being off for a while then get hot and do the start to run thing. I also checked the coil and it is toast--it is leaking like a boat without a drain plug (exaggerating-but it's bad) . I have spent all the money I'm going too on fixing these multiple issues so I'm going to have EVERYTHING replaced. Heck the AC is 20yrs and the furnace, blower, and coil is 12--I guess that's a pretty good run. I appreciate all the help.
 
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Old 10-22-14, 06:41 PM
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Update-well ended up the coil was leaking and had a blower motor going bad. Ended up getting a couple of window units and have been mulling over what to do since. I have figured I will change the ac next spring. In the meantime I have just changed the blower motor. The on and off with the blower was due to the blower getting hot and cutting out. So I changed the blower yesterday and have 220 from the main power but no power on the control board (no red light coming on) Do I need to check the transformer or just change the control board.
 
 

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