The Air Conditioning will not cool the 2nd floor

In a two level home, hot air will rise to the highest point making the upper floors warmer in the summer than the rest of the house. The upper rooms are the often the furthest point away from the air supply which requires larger ducts to compensate for the distance and if the duct work is not properly sealed, any air loss if noticed first at the point farthest away from the fan.  In some cases, the builder in trying to avoid having bulkheads on the 1st floor will squeeze the duct work into a wall cavity which can choke of the air supply.

Image of a AC system used in residential housing
Typical split AC system

If there is access to the main duct work, have a look at the joints and branch connections for duct sealant or foil tape to reduce air loss. Sealing up these connections can really improve air flow at the end of the long duct runs.   If the duct work is new, then it is fairly easy to tape the joints with aluminum foil tape or apply a duct sealant. If it is an existing system then you need to clean the duct of the joints first before apply sealant.   Cloth duct tape work too, but does not stand up well when used on heating systems.

There may be balancing dampers on the branch line of the ducts which can be used to reduce air flow to the lower floors and force more air to the upper floors. Be careful not to close off too much air or the AC will freeze up. The supply air grill is the rooms can be used to adjust the air as well. The cheap plastic floor registers have little slider to control the air flow that slide open or close. These can be difficult to try and balance air flow with but will work as an On/Off control.   A better floor grill will have an opposed blade damper below the diffuser that can be used to reduce air flow.

Poor return air flow is another common problem.   Make sure the is a clean pleated style air filter installed and do not use 1” wide high efficiency filters, these just choke off the air supply.  A 4” wide high efficiency filter works great by having a much larger surface area that cleans the air and still allows proper air flow.

image of a partially frozen AC evaporator
Partially Frozen

If you can remove the filter while the fan is running, try to slide the filter out a few inches and let go. If it gets sucked back into the filter rack it can indicate a strong negative pressure in the return air duct.

Another common is issue freezing of the evaporator coil. A partially frozen coil will choke of the air flow. Leave the AC off for a few hours with just the fan running and then turn the AC on. Let it run for 15 minutes and check the temperature of the air supply. It should be above 50°F or 10°C, any lower and the evaporator coil can form ice. The ice can slowly build up and reduce air flow.

These are a few of simple steps that DIYer can do but never attempt to modify the control, electrical, piping, sheet metal or refrigerant of any AC system, call a qualified technician for service.

Dirty Condenser Coils

The condenser coil shown here, was completely covered with seedlings from cotton wood trees. Every spring, these seedlings can quickly cover a condenser coil. If you cleaned the coil early enough, using a brush, it will just peel off the face of the coil.

Cotton Woods Trouble
Cotton Wood Troubles

The next image shows a small window AC with the outer cover removed. The back side of the condenser coil is very dirty. Dirt that has been baked on will need to be cleaned using coil cleaner and a pressure washer. A pressure washer must be used carefully, as it can very quickly bend over the aluminum fins on the condenser coil.

Dirty Condenser
Dirty Condenser

Keep the spray parallel to the fins and do not get too close. Hitting the coil with high pressure water at an angle will quickly flatten the fins. Where possible, try not to push the dirt further into the coil. Use a soft bristled brush to clean off the surface of the coil, then, spray the water in the opposite direction of the air flow, to push the dirt out.

In most cases, this is not easy to do. However, spraying in a counter flow direction will prevent the large dirt particles from becoming lodged deep in the coil.

“I have seen many units that look clean on the surface, but when you look closely between the fins, there is dirt packed in tight.  The dirt is very difficult to remove and also causes the unit to shut down on hot day.“

After spraying in a counter flow direction, switch to the opposite side and then try to work the rest of the dirt down and through coil.

Coil cleaners can be used to loosen dirt but be sure to completely rinse the cleaners off. Residual cleaning fluids left behind, can deteriorate the aluminum fins. If the coil is relatively clean, then just use water, it works well and is environmentally safe.

An air conditioning system works by absorbing heat from inside the building and rejecting that heat to the outside. If the heat cannot be rejected efficiently, the cooling process will slow down or even stop. Larger air conditioning systems, have a pressure safety device, that will shut down the compressor, if the pressure is high. Then, it may need to be manually reset, by cycling the power or pushing the reset button. Smaller systems, will use an internal pressure relief which is built into the compressor. The compressor operation will become very loud if this occurs or the compressor will shut off, on an internal thermal overload which should reset after several hours.

[Widget_Twitter id=”2″]