trane xl12 not cooling
 

Hi,
I have a Trane XL12 not cooling . yesterday the system froze up. Found the outside coil was clogged with dirt . washed out the coils and restarted and system cooled house down to 68degrees and seemed to work ok and ran fine for about 17 hours then if started getting hot again.It was 88 degrees both days. Furnace blower blows, outside fan blows, can't tell if compressor comes on. hooked gauge to the low pressure side with system off and was reading 120lbs. turn system on outside fan came on but the low pressure side still read 120lbs. If the compressor is working the low pressure should drop and hold around 60lbs right?? I don't know what controls the compressor. I know the outside fan has a capacitor to start it and it does run ok. I set the theromstat at 68 degrees and noticed the house lights dim every 20 minutes or so and the dim only lasts about 3 seconds then the lights brighten back up. I am thinking that might be the compressor trying to start and then giving up.any help would be greatly appreciated.
thanks, James

Does your compressor have its own start capacitor? If the lights dim, then it would be the compressor trying to start. The compressor has a internal over load that kicks off if it if it gets hot. Did you check the line volt out side?
If you are trying to bring your house down to 68, you might be freezing up your indoor coil, which would over heat your compressor. Let it stay off for a few hr.s and then try restarting it. Paul

yes it has it's own start capacitor, a run capacitor, and a capacitor switch relay. during testing after being off for 2 hours the compressor would start the first time. then it would cycle off and then when it went to restart the compressor it would try and start for three seconds then quit trying . wait for about 10 mins. then it tried to start the compressor again. Looking at the capacitors i found the run capacitor was swollen up and bulging. I replaced the run capacitor and it's been 36 hours and the system seems to be working ok with the temp set at 70 degrees. I would have thought it would have been the start capacitor that would have been bad. but by Trane part numbers replacing the run capacitor seems to have fixed the problem. Go Figure ????

The start cap. is just for starting. A run cap helps make the compressor run cooler. So if the run cap. is bad, the compressor gets hot so the start cap can't start it. After the unit has run for a while check the large copper line out side and see if it is cool. This is what helps cool the compressor. Paul

Thanks Paul for explaining how the system works. Now I understand why it was the run capacitor. Thanks, James