What happens when your filter clogs up with dust and debris? The effects of a clogged HVAC air filter in your air conditioner or heat pump can cause failure of the system operation that will result in a call for an air conditioner repair service.
An AC, heat pump, gas furnace, electric furnace, or even an oil furnace needs the proper amount air flow across the coil or heat exchanger to operate properly. When the filter clogs the air flow is minimized the blower works harder and harder to pull the proper amount of air across the coil or heat exchanger. What are the effects of a clogged filter in your HVAC system?
Serious Harmful HVAC Issues Caused by a Dirty Clogged Air Filter
- Cause your air conditioner to stop cooling
- Cause your air conditioner to freeze up and when it thaws the water from the melting ice can overwhelm your condensate drain and cause water damage
- Cause a serious mechanical issue with your compressor in your air conditioner or heat pump technically referred to as liquid slugging
- Cause your furnace and/or heat to stop heating
Effects of a Clogged HVAC Air Filter
- As the system airflow is reduced from a restricted and clogged filter your air conditioner or heat pump (in cooling mode) evaporator coil will begin freezing up resulting in less and less air flow from the supply vents. The refrigerant is still flowing through the coils but with no air-flow, there is no heat absorbed into the coils and refrigerant. The refrigerant falls below the freezing point and any moisture in the air around the coil begins freezing. It effectively turns the air conditioner or heat pump evaporator coil into a freezer. If the air filter is changed then you will still have problems until the evaporator coil is defrosted. With an air-conditioner, you turn it off for several hours to allow it to thaw. With a heat pump, you can simply turn it to heat mode and it will automatically defrost the evaporator coil. This problem can cause serious water damage to your home or business.
- Furnaces with clogged air filters will stop heating. As the air flow is restricted the heat in the heat exchanger gets higher and higher. Designed into every furnace are limit switches that will open when the temperature exceeds a designed temperature. When the high limits open the burners turn off and the heat stops. Many times these are automatic reset switches and will automatically reset when the temperature of the heat exchanger cools but if the clogged air filter is not corrected then the problem will recur and the furnace will not provide the proper amount of heat. Sometimes the limit switch will get stuck in the open position resulting in a service call from a contractor to replace the part.
Pressure in the System and Effects of a Clogged HVAC Air Filter
The pressure in the HVAC duct system and air handler are very important. If your system was designed correctly the designer designed the system for a specific amount of pressure as recommended by the manufacturer of the equipment. When your filter gets dirty you change the pressure inside the system and by doing so you change the amount of airflow flowing through the air handler and ductwork. There are other ways to change this pressure inside the ductwork such as closing off too many supply vents, a bad blower motor, or collapsed/restricted ductwork, but here we are focusing on dirty air filters. We have covered those other things in other articles if you want to browse our other articles for that information. Here is an example to illustrate the pressure in the system:
So you can see from the chart above the manufacturer recommends a design pressure of .05″ water column. If this was your system then it should be designed and balanced to achieve that pressure. At that pressure, we get the other variables listed and highlighted on the chart. CFM’s, and temperature rise. This is also the design pressure needed for the evaporator coil to function properly. When you have a dirty clogged air filter, you change all that including the pressure, the CFM’s, the temperature rise, and the proper functioning of the evaporator coil. That leads to problems that will affect your comfort.
Effects of a Clogged HVAC Air Filter
The effects of a clogged air filter in your HVAC system can end up causing damage to the air conditioner, heat pump, or furnace so make sure you keep the air filter clean and free of debris. One other big mistake that will have the same effect of closed off supply vents. Anything that reduces the air flow in your HVAC system is not good for it. Keep the supply vents open and filters clean and avoid costly repairs.
Effects of a Clogged HVAC Air Filter - HVAC
To learn more about heating systems and HVAC use this resource.
See the About the Author page for information about the author of this article.
Gas Furnaces Sequence of Operation | Electronic Ignition Gas Furnace Problems Troubleshooting | How To Light a Pilot Light | Heat Pump Breaker Trips | How Heat Pumps Work | Heat Pump Sequence of Operation | Condenser Fan Motor Repair | Air Conditioner Compressor Troubleshooting | Fuel-Gas Code Overview | SEER Definition | Air Conditioner Reviews | Boiler Reviews | Heat Pump Reviews | Heat Pump Problems | How to Wire a Thermostat | Goodman Heat Pump Reviews | Weil-McLain Boiler Reviews | Rheem Package Unit Reviews | Troubleshooting Broken Thermostats | Trane Versus Carrier Gas Furnaces | Carrier Heat Pump Reviews | Rheem Heat Pump Reviews | Trane Gas Furnace Reviews | Amana Gas Furnace Reviews
Share your HVAC Photos or ask a question about your HVAC System by uploading a photo of it.
Have a forced air furnace with a filter. Was wondering if additional filters in the duck system outlets would hurt the furnace.
Have been told any additional filters would harm the furnace. The extra filters are kept clean.
furnaces need a certain volume of airflow and filters will block the airflow or reduce it. Get an electronic air filter.
You mentioned that a clogged air filter can make it so that your AC stops cooling and your furnace stops heating. I think that is what is going on with our HVAC system. We have been thinking about calling in someone to take and look and see what is going on. We will have to see if changing the air filter makes a difference.
In our A/C system the filter was very clogged. We called technician and he told us that compressor has gone bad it needs to be changed. Did the compressor go bad because of clogged filter?
It is a possibility yes, however with any major repair I always advise a second opinion even though it will cost you to get the second opinion it will be cheaper if the second opinion reveals the compressor to not be bad. Condemning a compressor is difficult in some situations simply because most compressors are hermetically sealed and cannot be disassembled to see the broken parts.
I crawled under my double wide mobile home to instal a ice maker water line for my new fridge. I noticed my vapor barrier was dropping really bad in one spot. I punched a small hole in the barrier material and water started pouring out. Had the mobile home dealer in to locate the leak. They told me it’s the A/C. They called in the A/C man and he said the filters across the condenser were so clogged that water was dripping straight down into the heat exchange and this was causing the water to collect in the barrier. Does this sound like a correct diagnosis?
Yes, it is entirely possible that is what occurred. I would also check the drain for the evaporator coil pan to make sure it is not plugged and that it has a proper trap. It also needs a grade to drain. All these things I would check to make sure this does not occur again. I would also replace any ductwork that got wet if it is flex duct. If it is hard duct I would make sure it was dry inside and out and then re-insulate.
Hi,
I had my 22-year-old Trane XE80 furnace serviced and the repairman said to change out my filters to an electrostatic one. Since then, the pipe on the outside of the furnace has been freezing up during the cool mode. The repairman came back and said that the new filter is too dense and that is why it’s freezing up. While he was here I pointed out a cord coming from the furnace which was not plugged in and asked him if that could be the problem. He told me it was needed for the old filters but it doesn’t need to be plugged in for the new electrostatic filter. Does this sound right and can I plug in the cord and use it with the new filter?
Not enough information. I do not know what the cord is hooked to. Maybe an Electronic Air Cleaner? Maybe an Ultra Violet Air Cleaner? You can take a photo and easily upload it so I can see what you are talking about here. Either way, with a UAV or an EAC you still need a filter and to maintain proper air flow. Both the EAC and the UAV need maintenance from to time also.
Hi,
Thank you for getting back to me. The cord is hooked up to nothing. It’s coming from the side of the furnace and just hangs. The repairman said it’s used to force air through the filters but since I got an electrostatic filter it is not needed any more. You asked for pictures but there is no place on this form to submit them so I guess I will need your email address.
Thanks,
Debbie
I still do not know what you are talking about. The menu to the right – you will find “HVAC Document & Photo Uploads”. Click on that and it will take you to the page where you can upload photos.
Okay Debbie, I do not know what it goes to…………….off the top of my head there are three possible things it could be: 1) a plugged for an electronic air cleaner 2) a plug for an ultraviolet air cleaner 3) a plug for a condensation pump (least likely of the three). Either way this plug being unplugged is likely not your problem. You have a problem with air flow if its that critical that using an electrostatic air filter will cause the system to freeze up. The best way to solve the problem is to have a technician test the pressure differential from one side of the evaporator coil to the other. The pressure drop from the return to the supply side of the coil should be anywhere from .3 to .6 inches of water column. This is simply a ballpark but the pressure drop across the coil should be in the manufacturers literature somewhere…………hopefully you still have it.
If the pressure falls out of this range as recommended by the manufacturer then you have a problem with airflow that could the result of: 1) a dirty filter 2) a bad blower motor 3) improperly sized duct 4) damaged duct 5) a dirty evaporator coil. I have found, working as technician, all of these problems causing issues with air flow in HVAC systems. When you put in the electrostatic air filter you decreased the air flow across the coil. Electrostatic air filters are good filters but they load up faster than normal filters and cause the blower to work harder. I would start with the static pressure test first and then look at the other things I have explained to you here. If I was a betting man I would say your evaporator coil is dirty. In some cases the coil can be cleaned without disassembly of the duct work or the refrigeration system. There are some systems where I had to cut the coil out from where it was located and take it to a car wash and wash it with the high pressure nozzle (no kidding…the coil was that dirty).
In any case, then you can discover where that mysterious cord goes…..and once again, if I was a betting man I would bet it goes to an ultraviolet air cleaner. As far as the tech saying it is something to force more air…………….I have no clue what he is talking about…………..never heard of such a thing. What forces the air flow is the blower.