Why Is My Air Conditioner Freezing Up?
You’ve probably already guessed this isn’t a
normal part of the operation of your air conditioning system and you would be
correct in that assumption. If you’ve never experienced this, the idea can seem
far fetched. After all, not many people are used to seeing a block of ice
surrounding their compressor on a 95-degree summer day. Air Conditioning and
Refrigeration systems freeze for different reasons depending on what is
impacting what part of the refrigeration cycle (see below) These reasons can be
listed under 4 different categories; airflow loss, refrigerant loss,
mechanical, and temperature.
The first
reason for you’re a/c system freezing is probably the most common. The freon
pressures in your system rely on the absorption of heat in the evaporator
section. This is typically transferred from air that is pulled in from your
house into the air handler unit and across the evaporator coil. With a loss of
air flow comes a drop in temperature below freezing at the evaporator section
causing the water molecules in the air to form frost on the indoor coil which
eventually builds into a layer of ice. The most common cause for airflow loss
are listed below.
1.
Dirty
filter at the return air duct on the system, or too restrictive of a filter (filters
have a MERV rating, the higher the rating the smaller the particle it will
filter)
2.
Burned
out Indoor Blower Motor, or Motor that has too weak a capacitor to start the
motor. Often times a humming noise can be heard at the air handler unit
3.
Bent,
or Broken Blower Wheel unable to turn and provide airflow. A dirty blower wheel
will often cause motors to fail prematurely and will not move enough airflow.
4.
A
dirty evaporator coil, usually caused by the lack of a filter at the return, or
too infrequent changing of the filter (very common) This requires the
evaporator to be pulled and cleaned professionally
5.
Improperly
sized duct work, crushed or collapsed duct, insulation blown loose in system
blocking air flow. Improperly installed duct work
6.
Blocking
of the return air grille either with furniture or other obstruction
7.
Too
many Vents or Registers closed
The second
category is refrigerant loss. This is another very common cause for a/c systems
freezing over. Each system is charged with an exact amount of refrigerant or
freon that is used to transfer heat from your home. Age of a system, improper installation,
acidity of refrigerant, or manufacturing flaws can cause systems to leak
refrigerant. The size and severity of the leak is situation dependent. Loss of
pressure in the system cause the temperature of the refrigerant to drop below
freezing temperatures and form ice on the evaporator coil and travel outside to
the condenser via the copper lineset. In rare cases overcharging a system may
result in no superheat and the air conditioning unit to freeze over.
Other causes
of an air conditioning system freezing are mechanical related and are listed
below.
1.
A
clogged liquid line filter drier. Which is typically a result of a poor quality
installation, and improper evacuation during installation of a central heating
and air system.
2.
A
kink in the liquid line, or restriction in the system at the TXV (thermostatic
expansion valve) near the entrance to the evaporator coil.
3.
Liquid
line valve not fully opened.
4.
A
restriction in the metering device (see picture below) which can either be a
fixed orifice, capillary tube system, or TXV with a faulty power head. This can
also be related to poor installation practices and lack of filtering device
installed in system.
The last cause for a air conditioning system freezing
over is temperature. When we are referring to temperature in this circumstance
we are typically talking about the outdoor ambient temperature. A low outdoor
ambient temp can cause the pressures in the system to drop below normal and
cause freezing of the air conditioner. This problem is typically resolved with
a lockout device installed on the air conditioning unit by the manufacturer. Not
all systems are equipped with this type of control though. Typically running you’re
A/C system in outdoor ambient of below 60 degrees is not reccomended. Freezing
can also occur when the indoor temperature at the thermostat is set too low. This
puts unnecessary wear and tear on the system. On a residential system the indoor
temperature should not be set below 68-70 degrees unless equipped with controls
that prevent a freezing over situation.
When the air conditioning system freezes over it can
cause the freon to return to the compressor in a liquid form and cause slugging
of the motor. Modern scroll compressors are better equipped to handle this
situation than older style units. However, it can still cause damage to the
system and should be assesed by a professional if it ever occurs.
The friendly
professionals at Top Gun Air can provid an honest assesment and leak detection
service if needed. For scheduling of appointments check us out online. If you have questions
regarding freezing of your system and would like to speak to one of our helpful,
friendly staff, give us a call at (682) 214-0431. We hope you find this
article informative and helpful.
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