central air unit in my home...blowing hot air.....?

Question

circuit breaker is ok...digital t-stat shows 80'F and is set @ 72'F..outside fan is not running and i hear a slight noise from maybe the a/c compressor...is there anything i can check with a multi- meter or with a set of a/c gauges...help...!!!!!

Answer 1

Make sure the disconnect at the compressor is closed so voltage is getting to compressor. If it was closed, then check out the relay voltage.

Read below fully before you try anything.

It sounds like the thermostat signal to turn on compressor is either not being made, not being sent, or not being received.

1. With conditions you describe the thermostat should be providing voltage to the relay that turns on the compressor. Usually this is a 24 v AC signal (and is 0 voltage when off). At compressor look for a low voltage, very thin wire. Cut voltage off to compressor by opening the disconnect. Trace this back to the furnace and then to the thermostat. Measure the voltage at the thermostat output. If it is 24 volt there, the thermostat is OK. Now check at furnace, if 24 volt is there OK, if not the wire between thermostat and furnace is bad (not likely but could be). If ok, check at compressor. If 24 volts, then the voltage is good and the relay is probably bad, if not the wire is bad. BE CAREFUL AT THE AC COMPRESSOR. Be sure to have the disconnect open (no high voltage at compressor) when you do this.

2. Check the relay contacts. Beetles, lady bugs, etc have often blocked electric contact. BE SURE TO HAVE THE ELECTRIC DISCONNECT OPEN AND CIRCUIT BREAKER OFF BEFORE YOU TOUCH THESE CONTACTS AS THE VOLTAGE IS LETHAL. Clean contacts if needed; if they are badly pitted, replace the relay.

This should provide voltage to the unit.

If it still fails to start the compressor motor is probably the problem and it needs to be replaced or rewound.

Answer 2

You should do everything above, plus you should take a good look at the 'gills' - sorry, I am not a pro with the terminology) on the unit to be sure they are not clogged, especially if you don't have the unit cleaned out on a yearly basis. Our unit was doing the same thing, and along with feeling as if we were living in a sauna, we were getting clobbered with high electric bills since the unit had to work harder to get some air through the 'gills'. We ended up pulling out the indoor section of the unit and cleaning out what was a surprising amount of dust and hair (we have cats), and the outside unit was chocked with dust.

There are special cleaners you can buy from hardware stores and Lowes that will help remove any crust or dirt.

Answer 3

on the outside unit check to see if the contactor is buzzing...the contactor is what turns your outside unit on when the thermostat calls for a/c....you can read for 24 volts where the two low voltage wires(thermostat wire) connect on to the contactor or relay...the main power leads (240 volts) connect to this contactor.....there is a few reaons why you might not have 24 volts on relay...1 low freon swtich has unit disabled..2 time delay relay is bad...these items cause your unit to not start for a a minute or two if you lose power..3 manual high pressure switch...if it has one it will be somewhere around where the freon lines come out of the unit........If the contactor is buzzing and the unit is not running then you have no power 240 volts or capacitor is bad....all a/c have two circuit breakers..one for inside unit and one for outside unit...