Sorry for the illegible characters at start of sentences (done from iPhone Notes App). Here is the repost (preview look ok):

I moved to my current home about 11 years ago. The air conditioner unit Carrier model 48kha, kla was already installed on the roof; I have no ideas when it was installed. Since moving in I only have it serviced/repaired one time, that was about 7 years ago when I heard kind of a banging noise and then the unit blows out hot/warm air when it supposed to be cooling. If I recall correctly, the problem was a loose compressor and the service guy repaired. Since then it been running OK although I do notice the cooling air is not as cool as before over the years and becoming noisier. Now since yesterday, the air conditioner cannot cool down the house any more (the temperature remain the same after running it for more than 1 hour). I noticed when I turned on the air blowing out seems cool but after a few minutes it became basically neither cool nor warm. I also noticed that it does not discharge water (dehumidifying?) since. What is the likely problem and what is the general cost for this service? Please advice, thanks!

This seems like a really common problem for air conditioners. Having an air conditioner blow out everything but cold air is definitely something that is counterproductive. I would definitely suggest having a professional come out to look at your HVAC system as soon as possible. I am sure that it would be really nice to get it fixed before it starts getting too hot outside.

http://quickservant.com/cooling-baltimore-residential-air-conditioning-cooling-installation-services-howard-county-md.php

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Common Problems With Air Conditioning.

Open Windows

One of the most common problems with the cooling system in your home is occurs when doors and windows are left open. You might be surprised at how often just being vigilant about doors and windows can significantly improve the cooling process for your home.

Low Refrigerant

Refrigerant is the chemical that cools the air within your AC system. Low levels of refrigerant could mean there is a leak, or an actual problem with the refrigerant system. If your AC system needs to be recharged, most of the time that suggests there is a leak.

Leaky Ducts, Bad Air Flow

Leaky ducts or improper air flow are another very common culprit for why your AC is not cooling properly. Inconsistent temperatures often are an indicator that this is the problem. If there is a leak somewhere in the line then the cool air that is moving from your unit through your home is not making it all the way to where it needs to go.

Filters and Coils

Check your filters and coils. A dirty filter or coil will restrict your air flow and keep your machine from running at peak efficiency.

Clogged Drain

A clogged condensate drain on your unit can cause loss of efficiency and cooling. It is best to get a certified HVAC technician to check this for you, it is bit more technical and it is better to be safe than sorry. If you break something it could cause a much more expensive repair later on.

Outside Fan

The outside fan is responsible for conveying the heat from your home to the outside air. If the fan on the outside isn’t performing correctly, the proper heat transfer cannot take place, the air conditioning compressor may overhead and trip the safety overload.

Solution

The best and most effective way to prevent these problems is by participating in a preventive maintenance program. If you would like help with your air conditioner from a professional.

Mistakes you Can’t Afford to Make With Your Air Conditioner.

https://www.heatair.org/

1. Size Requirement Issues

Air conditioning systems work by cooling a specific number of cubic feet per unit. When choosing the unit that is right for your home, make sure that you find one that is rated specifically for the area that it will need to tackle. If you buy one that is too small, it will have to work overtime and that will decrease its efficiency and lead to breakdowns. If you choose one that is too big, it won’t run enough, which will not help reduce the humidity levels in your home for a more comfortable environment.

2. Dirty Cleaning Coils and Fins

Cleaning both the coils and fins is essential for your ac unit to work optimally. The coils and fins are responsible for its operation, but if they are caked with dirt and debris, then they can’t work as they should. And over time, that will lead to a decrease in energy efficiency and higher monthly bills for you. It can also result in the need for an ac repair call.

3. Air Filter Exchanges

The air filter is responsible for removing dirt and debris from the system. They should be changed every six months or less to ensure good air flow and to increase the air quality within your home. If you don’t change them frequently, it reduces your air conditioner’s efficiency by as much as 5 to 15%, which can really add up over the long, hot summer!