Air Conditioning - A/C not cooling

I have a two Carrier units (one for upstairs and one for downstairs). We have a recurring problem (seems to happen every year) where the fan runs, but the unit does not cool. Sometimes, this corrects itself in a day or so. But this time, it has not. I have changed all the filters, and checked the coils on the units, and they are not too hot or frozen. The breakers are not tripped.

The units seem to run and run, whether it's set to "fan" or "auto", but things don't cool down. I did change a filter downstairs, which had not been changed as it should have been, and was very dirty. The downstairs appears to be cooling down now. Could a dirty filter downstairs affect the functionality upstairs? I am lost! Before I call for an expensive service call, does anyone have any ideas that could help? I know NOTHING about HVAC systems, but would love to learn anything that may help with this.

(It has been VERY humid outside, and we have just gone from a very cool spring to a drastically hot day yesterday, and this is when the a/c failed...)

Thanks!

You must live in the Mid-Atlantic region. The past couple of days have been a major change. I suggest you feel the copper lines on both units for a comparison. The big line should be cool to cold & wet. The small line should be warm to almost hot. If they are not as described, something is not right. If both the small & large lines are about the same temperature there is no compression taking place.

Grady,

:) You are right. We live in central North Carolina. Thank you for the advice. I will check right away, but a couple of hours ago, I think the lines were about the same temperature, so it could be the compressor...? Is that an expensive repair?

If the fan on the outdoor unit is running but the lines are about the same temperature, no compression is taking place. This can be anything from a simple & inexpensive capacitor to a bad compressor, neither simple nor inexpensive. Without some testing nobody knows.

I have a TRANE air conditioning. I have exactly same problem. Both lines are same temp. what test I have to do to determine if it is a capacitor or compressor problem.

Thanks in advance.

fist i would visually check the cap, if it is swollen, it is bad. checking the output of the cap and the compressor windings is best left to a pro, lots of variables, and you may condemn a good one without knowing it

Be sure to check the voltages. I posted earlier because my unit was blowing hot air. We checked the voltages as recommended in the forum and found they were low. The only sound from the outside unit was a clicking when the thermostat was turned to cool. Check the fuses next to the outside unit, the wiring, and the main breaker or fuse. We found a fault at the main breaker box. We fixed it and now we are cool again. Good Luck!