I live in a condo, have an outside (ground level) heat pump and an upstairs air handler in the outdoor closet. The AC is blowing warm to room-temperature air through the vents.

I've check out the air-handler. No freezing up, air filter was recently replaced and it seems to be functioning properly. However, on the outside heat pump, the fan does not seem to be running at full speed. It's also oddly quiet, so I'm pretty sure the problem is there in the heat pump, but I really don't have a good idea of how to troubleshoot from there so any help would be appreciated.

I hate to say it, but when it comes to these type of systems, it really is best to call in a pro. Certain diagnostic tools and knowledge are required to correcty troubleshoot ac systems, let alone heat pump systems. Couple things you can do. Look in the outdoor unit to see if the dual capacitor is bulged at all. A bad cap would explain the slow running fan and the quiet noise(due to compressor not kicking in). Many times you can tell if the cap is bad merely by looling at it. If you aren't sure, just pop a couple pics of the inside controls and capacitor of your outdoor unit and post them here. At this point, I would lean towards a bad capacitor, but without seeing things and being able to put my tester to equiptment, its really nearly imipossible to give a good diagnostic. Good luck, and please let me know what you find.

Thanks for the tips, even if I'm able to find the exact problem, I plan to call in a professional to do the work. Just always good to know the problem before hand in an effort to not get ripped off. I'll take a look tomorrow in the day light and let you know what I see. Thanks for the reply!