I have two AC Units. One for upstairs and one for downstairs. The upstairs one works just fine but not the downstairs. So, i did a test by turning both units on and went outside to compare the two units. The upstairs one works fine and blows out warm/hot air, but the downstairs one seems to blow out cold air compare to the working unit. These two are not heat pumps. They are both AC units. Anyone know what is wrong with my downstairs unit? BTW: I had the HVAC guy come out to check it 3 years back, and he added refrigerant into the system. It worked for a week or two after he left, then it's back to warm air again. Would this be a leak of some sort? Because of the need to capture the refrigerant and licenses to get the refrigerant in most places, this typically isn't a DIY job. The fact that the outside unit is running and air is blowing inside suggests that it's not a problem with the thermostat. Check the breaker, air filters, and any other easy to access components for obvious problems.

Beyond that, there are a lot of possible issues:parts of split ac unit No refrigerant or not enoughhow much to replace inside and outside ac unit Controller has failed or wiring has become disconnectedenergy efficient ac and heating units Inside coils have frozen over Since the first two are the most likely and either will need a professional to repair, you may as well get one out to diagnose the problem for you. It's either a dirty unit or a capacitor problem. If the unit is very dusty you need to clean out the dust to let it breathe. If the capacitor went bad, when you look at it the top will be bubbled up. Most likely it's the capacitor. Change your filters: a dirty filter is what an AC mechanic loves;

it's money in the bank for him.Browse other questions tagged repair hvac air-conditioning or ask your own question.Is the thermostat the problem? When we have our central air fan set to "on," it runs fine, but when we set it to "auto," the fan does not come on even though the AC compressor kicks in.  (The AC unit is working fine...It comes on and produces cool air). This means that we have to keep the fan on constantly when we want the AC on.  Do we need to replace the thermostat? It didn't seem to have this problem throughout the winter when we had the heat on and the fan set to "auto." Not what you were looking for ? Ultimately, you may have to replace the thermostat. But before you do, try these steps: 1) Thermostat switches make electrical contact across two very small conductors that carry a very low energy signal. This means a low-energy battery, without enough energy to create the required signal, can result in problems like you're experiencing. First step ... purchase a fresh battery and replace the old one. 

Move the temperature and fan switches to the "Off" position and then return to your preferred settings. Allow several minutes for the thermostat to "cycle." Then determine if the compressor and fan have come on; 2) Because the thermostat conductors are very small, if the switches are slightly out of position and they will not conduct the required energy to transmit a signal to the fan and compressor. Try simply wiggling the switch back and forth gently across the "Auto" position and allow it to stop as you feel it click into the "Auto" position. Allow several minutes for the thermostat to "cycle" and determine if the compressor and fan have come on. These are two easy steps that may allow your system to work. Since you report the thermostat working fine in the "Heat" position, I would expect it to work just as well in the "Cool" position. I hope one of these simple fixes works! However, if these steps do not work, thermostats are relatively inexpensive and the included instructions make it fairly easy to install.

Make certain you purchase a thermostat for the type system you have (ex. heat pumps often take a different thermostat that compressor systems). Then, pay attention as you remove the old thermostat and reinstall the new thermostat following the color codes on the instructions. Finally, if none of these steps work, have a reputable licensed AC contractor service the unit. Most units that are serviced regularly provide efficient service for many years. I have taken these steps many times in the transition between heating and cooling seasons, and I'm always pleased that I didn't turn a small repair into an unnecessary, much larger repair bill. NOTE: This is a great time to change your air filter. Check the size and purchase a replacement while you're at The Home Depot. A Plumbing Associate will be happy to discuss your options. Relays/capacitors are commonly damaged by power surge ... lightning is a common enemy of this part! The visible indicator is the canister swells like it wants to burst.

Relays are beyond most DIYer's desire or ability, so I didn't include it in my earlier list. If you were able to identify the item, a local A/C supply house would likely stock the part and may or may not sell it to you ... some require licensure to sell any of their parts while others will sell non-regulated supplies to anyone. Unless you are particularly handy with electrical, I would save my resources for that reputable, licensed repair shop. You may find the solution another way, but having your annual service and including this repair is likely a good idea. I really like to "Fix It" when I can, but there are times when you just have to let go and call a pro! This may be one of those times. A Quick Warning: "Start Relays/capacitors" build up energy and discharge that energy to help start electric motors. This discharge can give you a very real shock!!! Be very cautious if you decide to proceed on your own. You are soo welcome, Jennie! When you resolve the problem, take time to come back and explain what you found and how you resolved the problem.