AC goes on/off

[John H]

Say the thermostat says its 82 in your house, I set my AC at 78. It will go on immediately like its supposed to, but then after a couple minutes it goes off and its not even close to 78? Just goes on and off. Stays on for maybe 5 minutes. I know its costing me more for power just becuase to starting up more than it should... The thermostat is a digital one called Ritetemp... I replaced it a few years back from the original, those old round ones. I dont remember this happening after I replaced it. any ideas, TIA

[Joseph Meehan]

There are several possibilities including a vent near the thermostat triggering it early to a mechanical/pressure problem with the A/C unit.

I don't know, but maybe your new thermostat has some sort of anticipator for the A/C (anyone know if someone is doing that now?

[mm]

If you saved the old thermostat, you could put it back in place. I am not saying that so likely to fix it, but I don't know much about AC.

BTW, I saved my thermostat and I'm going to use it to notify the alarm monitoring company if the temp goes too cold in the winter.

[KC]

Thermal cutout on the compressor? Would that tripping remove the control voltage to the thermostat?

[Lamey]

That could be it, The anticipator is a good thing to look at. If you have one that is.

[Meat Plow]

Maybe the condensing unit is low on refrigerant or the A coil in the plenum is dirty or the filter is dirty or combination. You need a tech with a set of gauges to check high and low side pressures and give you a diagnosis.

[Lamey]

That would be me, I'm EPA certified and hace the gauges.

[Puddin' Man]

I'me not a pro but I've tinkered a fair amount ...

There are switch(s) in the condensing unit that prevent the compressor from running very long under unsuitable conditions, i.e. refrigerant pressure is too lo or too hi.

IIRC, under such conditions, the lite on the tstat stays on. Does yours?

If not, the tstat or the lo-voltage circuitry could be the problem.

You very likely need a conny-tractor either way.

P

"Mit der Dummheit kaempfen Goetter selbst vergebens!" -Friedrich Schiller

[Meat Plow]

High and low side gauges and an Amprobe on the CU main. An experienced tech does this right away for one, to prevent permanent damage to the CU and to determine whether it's a compressor issue or call for cooling/anticipater/differential problem.

I wuz a tech skool trained heat/cool tech/installer back in the late 70's :)

[Lamey]

Right on! We're walking the same path a little here. We must talk sometime.

[Meat Plow]

Do you hace a set of steel R-117 gauges like I do? :)

[Lamey]

Nope, old ones, It&#39;s been awhile. I worked on restaurant equipment for a while. The HVAC biz up here in taken. So I build log homes now. < sigh >

[Meat Plow]

heheh back when teh natural gas was cheep, a shit load of what we had for residential and soho around here was gas fired water chillers. I went to school at Bryant and Whirlpool, the two most popular unitz. Back in teh

70&#39;s you could chill your 2400 sq feet ranch house down to 40F in 100F summer heat for maybe 30 bucks a month. Ammonia is teh bestest refrigerant. I&#39;ve seen dairies and cold storage facilities running R-117 pumping that shit to their -30F rooms with V12 Caterpillar Diesel powered pumps. Just awesome man :)

[Stormin Mormon]

Could be any of a bunch of things. We need a lot more information than what you just provided. I may be able to help, if you can get me some more information. Interested?

[Deke]

It is probably over charged or under charged.

If it has a low pressure shut off switch, the compressor creates a suction that falls below the shutoff point, but then builds back up after awile and starts again after a delay timer expires.

[TBone]

While that would cause the compressor to cycle on and off, the blower fan should continue to run and the OP is making it sound like the entire unit is turning on and off. I would look at either the thermostat or the wiring from the thermostat to the unit for loose connections as a starting point.