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There are many reasons why your AC could stop working, or stop being as effective as it once was. You won’t be surprised to hear that many of these reasons require an expert repair person to fix. However, some air conditioning problems can be solved at home, with few or even no tools and no special training.

So, this article will achieve 3 things:

  1. Help you troubleshoot the nature of your AC problems
  2. Help you identify those problems you really need an expert to fix, and
  3. Help you solve some problems yourself, without the expense of having an AC specialist in.


Part 1: Troubleshooting

Why Won’t My Air Conditioner Turn On?

(or “No AC in house”, “No air conditioning I house”, “AC not working in house”, etc.)

This could be something quite serious, but it could also be something very simple. We handle a lot of complaints like this every year, and we’ve developed a simply troubleshooting system to get to the bottom of most common problems quickly. Let’s start at the beginning.

1. Is your AC unit receiving electrical power?

This is where practically every type of electrical troubleshooting starts.

  • Central AC units

For a central air conditioner you can skip right to checking the circuit breakers and fuses. Only try resetting the circuit breaker or replacing the fuse ONCE. If it trips again either immediately or after a short amount of time, you may have a serious electrical or mechanical problem with your AC.

2. Reset all the switches and settings on your AC, and try it again.

Assuming you’ve determined that there is electricity flowing to the AC, the next step is to reset it completely. The procedure varies from unit to unit, but should be outlined in your instruction manual.

  • If you’ve lost your instruction manual

This is very common. Most manufacturers will have .pdfs of their manuals and documentation available on their websites. If you don’t like computers, or simply prefer a paper copy, we can usually find one for you.

If you’ve reset the unit, and it still doesn’t start working, move on to step 3.

3. Check the setting on your thermostat.

All AC units have thermostats. Make sure yours is set to a temperature lower than the actual temperature in the house. I know you almost certainly have already done this and you’ll feel silly doing it again, but you’ll feel a lot sillier paying a repair person for a service call just to turn one dial and leave.

Assuming the thermostat is set correctly, move on to step 4.

4. Check your air handling unit.

Turn your AC ‘on’ and set the thermostat very low. Now, go to your air handler. Can you hear the motor running?

  • I hear the fan motor running, but no air is flowing

In this case, you may have to replace the blower’s belt. We’ll detail that below.

  • I don’t even hear the motor running

Check if the motor itself has a fuse which can be replaced, or if something else is preventing power from getting to the motor. Otherwise, you may need a new motor, or even a whole new air handler. Best have a repair person in the check before doing something expensive, though.

  • The motor is audibly humming (and / or heating up) but not turning

This usually indicates a serious problem with the motor. Shut it down, and call a repair person.

5. Check the ‘float switch’

This is also called a ‘drain switch’ and a ‘condensate overflow switch’. This is a small electrical unit that serves the same purpose as the float on a toilet reservoir. If your condensation drain is stopped up, blocked, or not working correctly for any other reason, the water level in the pipe or drain will rise, and lift the float. This will turn your AC off to prevent additional condensation form forming, and prevents water damage to your home.

This is one of the very few tests it is advisable to make with your AC unit on. Simply lift the switch unit out of the condensation drain pipe (it is not generally secured, and should lift out easily). If necessary, manually place the float in the ‘down’ position.

Does your AC turn on? Is the pipe full of water?

  • If the pipe is full of water and depressing the float turns your AC on, you’ll need to sort out the blockage in your drain pipe. That might or might not require a plumber, and is beyond the scope of this article.
  • If the pipe is full of water but depressing the float does NOT turn your AC on, you need to sort out the blockage AND you may need a new float switch.
  • If the pipe is empty and depressing the float switch does nothing, you probably need to call in a repair and maintenance specialist.

Why Is My Air Conditioner Blowing Hot Air?

What it comes down to is that your air handling unit (fan, blower, etc.) is running, but something is wrong with the cooling parts of the system. There are several things which can cause this, ad this troubleshooting guide helps you determine what the trouble might be.

1. Turn the power off to the AC unit.

You really don’t want to perform any kind of maintenance on an air conditioner with it powered on, for your own safety, and to prevent expensive damage to the unit.

2. Remove the air filter

Look at the filter, and determine if it is clogged, even a little bit. If it is, then either clean the filter, or replace it with a new one, depending on the requirements of your unit. Again, check the instructions if you are unsure how to do this.

If the filter is I good condition and isn’t clogged or blocked, go on to number 3 below.

3. Is there ice on the evaporator coils?

The ‘evaporator’ is the indoor section of your cooling system.

The next thing to do is check your evaporator coils for ice. If there is a build-up of frost or ice, your system will not cool properly. This prevents heat from the air delivered by the air handling unit from getting into the coolant – the ice itself acts as an insulator or blanket, cooling the air very slightly, but not enough for you to feel the benefit of.

Note that if this happens often, it might indicate problems with your air handling unit, a clogged capillary tube in the coli itself, or other, more complex problems. This is another indication that you should have a maintenance person inspect your system sooner rather than later.

However, it can be fixed in the short term (see below).

If there is no ice on the coils, move on to step 4.

4. Check your condensation drain and float switch.

See #4 above for details. It is possible (even likely) that your float switch will not turn off your air handling unit, but only the cooling features of your AC system. Basically, do everything we suggest for that entry, and if it proves fruitless, move on to umber 5. (This number 5, not the one above.)

5. Check over your compressor (the outdoor unit).

Your compressor has the job of literally squeezing the heat out of your coolant gas (compressing it back into a liquid) and dumping that heat into the air outside. If something is preventing that from happening, your AC will stop cooling your home.

  • Is your compressor working?

You might need a partner for this test. With everything plugged in and powered on, se the thermostat to well ABOVE the temperature inside your home. Wait 5 minutes. Now, stand beside the outside compressor, and turn the thermostat down to well below the current inside temperature.

If the compressor is working, you’ll hear it start, and see the fan start to move. If not, you may have a serious problem.

6. Check your refrigerant (Freon) levels, and look for refrigerant leaks.

You have reason to suspect a refrigerant leak if you notice:

  • Ice or frost building up on the refrigerant line or the outdoor (compressor) unit itself. (Note, if ice is forming on your INDOOR coils, it is more likely something else. See #3 above.)
  • A hissing or bubbling noise. (Note, this indicated a fairly rapid leak, and won’t continue for long. It is not a particularly good thing when the hissing noise stops.)

You might suspect you have low refrigerant levels (but not a particularly fast leak) if your air conditioner can keep your home cool on warm days, but can’t keep up during very hot days or the hottest part of the day.

Split AC Not Cooling Enough / Split AC Not Cooling Reasons why your split AC might not be cooling properly could include almost any of the reasons for central AC units mentioned above.

In addition, you may be using a unit that is far too small for the room, or can’t compete with insolation from skylights or large windows.

So, by this point you have either found one or more problems, or you haven’t. If you haven’t found the problem, you definitely need to have an expert come in. If you have found issues, the next question is, can you fix any or all of the problems yourself?

Part 2: AC problems you need to call in an expert to fix

If you’ve determined that any of these are probably (or definitely) the problem, then I’m afraid you really will need to have a professional come out and take a look.

1. Your compressor unit is malfunctioning

Your compressor is probably the most important part of your AC system. If t had a ‘heart’, that heart would be your outdoor compressor. It keeps the vital fluids moving throughout your system, and if it stops ‘beating’ your system is effectively ‘dead’.

Unfortunately, the compressor is probably the single most expensive component of your air conditioning system as well. If it is still under warranty, you’ll definitely want to let a professional handle it.

If it isn’t… You’ll probably have to replace it entirely. It isn’t really something an untrained handy-person can deal with safely or effectively.

2. Your condenser fan motor either doesn’t work or doesn’t work correctly

If the motor on your outdoor unit is bad, your AC won’t be able to dump heat into the air properly. Replacing a fan motor is a fairly big deal, and you should not really try to do it yourself. It may void any warranty you have if you try, and you could easily get hurt.

Still, here’s what to look for, and what it might mean:

  • Your compressor is audibly buzzing, and the motor isn’t turning

This could be a sign of a faulty capacitor. If so, the motor will not be able to turn, but power will continue to flow through one of its electromagnets. This causes the motor to overheat and (usually) switch itself off.

  • Your compressor is humming gently

A humming from the compressor – but no movement form the motor – indicates a possible fault in the low voltage transformer. This is difficult to tell from a buzzing motor, but the result is the same – call a professional.

  • Your compressor runs, but makes a grinding noise

This can be the result of worn bearings in the compressor motor. This will cause the motor to overheat eventually, and it will shut down. If you can hear a grinding sound, you’ll need a professional to replace the motor very soon.

3. Your air handler motor doesn’t work, or doesn’t work properly

Again, this isn’t something you should attempt unless you have proper safety training. Listen for buzzing, humming or grinding, but expect to have a professional replace the motor.

4. You have a refrigerant leak, or low refrigerant levels

If you already know how (or look it up elsewhere) and determine that you have a leak or low coolant levels, you really will need to call in an expert to top it up and mend any leaks.

Please do not operate your AC with low coolant levels, as this can damage your system beyond repair!

Part 3: AC problems that you usually can solve on your own

1. Thermostat issues

Again, I know you’ve already checked this, but when a service call could cost you as much as $100 the second the engineer steps through your door, it’s worth going over the basics.

  • Is the thermostat set too high?
  • If your thermostat is set to a temperature higher than the actual temperature in your home, it isn’t broken, it’s just doing what you told it to. Turn it down to 70 or so (depending on your tastes) and see if t starts working.
  • Is the thermostat set to “ON” rather than “AUTO”?

If so, the fan (air handling unit) will blow 24 hours a day, whether the actual AC is engaged or not. This will result in the AC ‘blowing warm air’ most of the time. Set the fan to ‘AUTO’ or the equivalent for that unit, as set out in your instruction manual. That should make it only blow when the unit is producing cool air.

2. Air filter issues

If your air filter is dirty or clogged, it won’t allow air to pass through your vents properly. Not only can this prevent proper cooling, it can be very bad for your AC system.

  • It can result in a unit that can’t cool your house enough, even they it does blow some cool air
  • It can cause your evaporator coil to freeze up entirely, further reducing the ACs ability to cool the air
  • It can fail to catch the dust, mildew and allergens that the filter was pu in place to block, reducing your overall air quality, and causing dust and contaminants to build up in your ducts.

So, follow the instructions in your manual to remove they air filter, inspect it, and clean or rel=place it, depending on the type of filter used.

Solution: Check the air filter and change it if it looks like the filter on the right

3. Your condenser (outside unit) needs cleaning

The condenser is the counterpart to the evaporator. It needs to be clean and free of debris to work. As it is located outside the home, it is more prone to getting dirty, and should be cleaned often, especially during the summer and just before you turn it on for the first time in spring.

  • Your compressor unit has a separate power system than the indoor parts of your AC. Turn it off either at the outdoor shutoff switch, or at your fuse box / circuit breaker panel. If you’re not sure how to proceed, check the manual that came with your unit.
  • Spray the unit down with a garden hose (it should be completely waterproof – it has to work even in the rain). Make sure to use a gentle flow of water, not a high-powered nozzle. Too much pressure could bend the heat exchanger fins flat, making it much less effective!
  • Cut any weeds or plants growing within a foot or so of the compressor. Tahy can slow airflow to the unit as well. For the same reason, cut back any trees or shrubs growing nearby.
4. Your air handler makes a rattling noise, which is conducted through your ducts

This may be because one or more of the air handler’s or furnace’s panels, access doors, or other parts are not secured properly.

Make sure all screws on the housing are tight, and that any doors or panels are secured appropriately.

If it still makes a lot of noise when it runs after that, you may have to call in an expert.

5. Your air handler belt needs replacing

Your air handler (blower, fan, etc.) may need a new belt if the old one has come away, or if it screeches often when starting, or whenever it is in use. Here are the steps to follow:

  • Disconnect all electrical power form the air handler before attempting to service it in any way. You could literally lose fingers by ignoring this advice!
  • If your air handler is part of your gas furnace, also turn off the gas at the valve that serves the unit.
  • Follow any other safety instructions listed in your owner’s manual! If you need a replacement manual, we can help.
  • Open up the air handler. Depending on the exact model, this might be a door which opens or slides, a panel that can be removed, or even a kind of drawer. Check your owner’s manual to be certain.
  • The belt should have a number stamped on it. Write this down, and order an exact replacement. Again, we can help with this, or with finding you a compatible belt if the original part is not available.
  • Slip the new belt over the motor pulley first. This is usually the smaller of the 2 by far, and won’t be difficult to identify.
  • Attach the belt to the blower pulley by getting it as close to ‘in place’ as you can, then turn the pulley by hand in such a way as to ‘drag’ the belt fully into place. Think of it like changing gear on a bicycle.
  • If this proves too difficult (buy you know for certain that you have the right size belt), you can provide a little slack by adjusting the motor’s mounting. There should be a screw or similar device specifically for that.
  • Make a note of the mount’s original setting, and return it to that same tightness after you’ve fit the belt.
  • If your owner’s manual lists a specific tension then you should reset the mount to supply the recommended tension. If you do not know the recommended tension, set the mount so that the belt will deflect no more than 1 inch when pressed firmly at the midpoint between the 2 pulleys.
6. Lubricating your blower motor

First, not all blower motors need lubrication. Check your manual to be sure. In general, if your motor has sealed bearings (many newer models do), then you should never attempt to lubricate the motor. If your motor does require it, follow the instruction in the manual.

Once again, though, many of these tasks require a bit of familiarity with electrical systems. If you don’t feel up to it, DON’T RISK IT! Call an expert and have your system diagnosed and repaired professionally.

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