Evaporator Coil Replacement Summary

Evaporator Coil Replacement Summary
One of the problems that we encounter in RAC is that the evaporator coil often leaks a lot
which is more than it should and there are many reasons why it happens. That’s why there are
appropriate steps needed to be followed when replacing an evaporator coil to avoid further
implications that may occur once you made a mistake. And here are the steps that are stated in
the video:
1. Make sure to know exactly where the leak is before you replace it. Because the evaporator
coil is prone to leakage and there are many types of it in the market that also have many
different systems, making the technicians often do not have the time to diagnose the entire
system. So, to efficiently confirm that the evaporator is leaking and to know where exactly the
part is leaking you can use a good quality leak detector like a heated diode electronic of an
ultrasonic. Now that you know where the leak is, make sure to leak check the entire system to
avoid missing any other leak if there is any before replacing it with a new one.
2. Get the refrigerant out. To do this, first, pump down the compressor to low pressure so that
you can only lose as little refrigerant as possible for cost-saving. Now then, you can take the
valve caps off by using a service wrench and closing the liquid line down. Then run the system
and watch the pressure on both sides of the suction and liquid line. And when the pressure
drops down to 10psi, that’s when you shut off the disconnect, while shutting down the suction
valve at the same time, just in case the compressor is also leaking. Then you can recover out the
last little bit but still keep slightly above the atmospheric pressure in the system when you open
it because you wouldn’t want it to suck air into the system.
3. Remove the evaporator. To do this, cut lines whenever possible and avoid unsweating
because refrigerant oil is flammable and can cause a fire. And if there is an old-line dryer, you
have to cut it out so you can easily place the new one. Now, when you pull the old evaporator
coil out, make sure that you keep anything from going in into the lines, and with this, flowing
nitrogen will be helpful.
4. You also need to keep some tapes or plugs. Because you need to plug up the ends of the lines
when you are not in the process of flowing nitrogen to prevent anything from getting into the
ends of copper. This is because leaving the copper open can make the Poe and PvE oil become
contaminated.
5. Put the new evaporative coil in, including a new metering device and drain pan. When you
put the new evaporative coil in, might as well put a new metering device and drain pan.
Because these two often break easily when you reinstall it. This will saves you time and effort as
well as money. Now, when you reinstall the new evaporator coil, make sure that its level and all
the retaining clips and the things you remove are properly placed back where you removed it.
After ensuring that everything is properly placed, that’s when you can braze back in your
evaporator coil with nitrogen flowing at 3 to 5 SCFH.
6. Once you get everything all brazed in properly. Make sure that everything is protected
because the brazing process is critical. After this, you need to do a pressure and bubble test on
all of the joints and ensure that the pressure is not dropping. You can monitor this by using
modern probes or digital gauges.
7. Pull a proper deep vacuum. Here, you can use the one hose or two hose method. But only do
this with the cores out and with large gauge hoses. And once it is all done, it holds your vacuum
with passing decay test then you can open your service valves, both the suction and liquid
service valves, and proceed to step 8.
8. Run the system. You need to run it in cooling for about 15 to 20 minutes. And it is a good
time to clean.
9. While the system is running, you can take advantage of that by cleaning the drain.
And once the 15-20mins is done, measure the suction pressure or the suction saturation
temperature, the liquid line, superheat and sub-cooling, delta t. And to be more thorough also
measure your delivered BTUs per hour and your static pressure.
These are the steps you need to follow when you are replacing an evaporator coil. And take
note that before replacing it with a new one, make sure to properly inspect and assess the
entire piece of equipment to avoid misdiagnosing and having an expensive repair that did not
actually fix the problem.
Why Does The Evaporator Coil Freeze (And How To Diagnose It) Summary
When you are working with air conditioning unit or refrigerator, it is normal that freezing takes
place in these units. And there many reasons why it happens. In these we are going to tackle
about freezing in an air conditioner specifically diagnosing and dealing with an evaporator. And
when diagnosing a freezing evaporator there are proper steps that you should follow. These
are:
Knowing where the ice in the system originates. Normally the ice if it exists start in that
evaporator coil and that is an undesired condition because you should not have ice on the coil
on an air conditioner running in cooling mode.
Step 1: If you find a frozen evaporator coil or any ice on an air conditioning system running in
cool mode, First you need to do is to fully defrost the system and the coil. Then check in the
order of air flow and look for the refrigerant restrictions then look for refrigerant issues. The
reason for this is because people rush to adjusting the refrigerant charge. This is not where you
start, start with the obvious signs of airflow then move forward from there. The first one to do
is to get the ice off, may it be allowing to defrost naturally or shut it off with just the blower
running in the case pf a fan coil with the blowers over the coil if it is a gas furnace and you have
a severely frozen evaporator coil, the you need to pull out the blower housing and try to
manage the ice as much as possible and as it melts use a shop vac. In some cases, you can use a
heat gun and don’t use any sort of sharp implement or any extreme heat to try to defrost. As
you try to get the ice off, try to do it as gently as possible.
Step 2: Check for a dirty air filter and don’t just check in one spot because in some cases you get
situations where people jammed a filter into a return or they’ve double filtered, so look
everywhere that a filter could before you check anything else.
Step 3: Check the evaporator coil cleanliness on both sides. In some systems, this is going to be
very difficult to do, and if it is very difficult to do, you can jump forward and do a static pressure
drop test across the evaporator coil if thats easier and look for the manufacturer’s
specifications in order to see if it’s out of range. But for most of us though, its just going to be as
easy to take a look at the evaporator coil and see if its visibly dirty.
Step 4: Check your blower wheel for cleanliness. Both of these cases, it they are dirty, you are
going to need to clean them. It is great if you can clean them in place but in many cases you will
have to pull them outside especially with the blower wheel, you can pull the entire assembly
outside and wash it out in the yard but always remember to remove the blower motor from the
blower wheel before you attempt to clean it.
Step 5: Make sure the airflow settings are correct. Always check your blower performance
charts for the particular piece of equipment you are working on. And make sure that the dip
switches or pins or thermostat controls are set up to produce the designed airflow needed for
the particular piece of equipment that you have. There are a lot of rules of thumb out there and
some of them can be helpful for a particular market but ultimately you need to know what is
the design airflow for the system that you are working on, what target are you trying to hit
because people may throw around 350 CFM per ton or 400 CFM per ton or 500 CMF per ton
but you need to know the design of your particular piece of equipment to know what target
you are trying to hit. Once you established that then you can do a total external static pressure
test on the system to make sure that you don’t have undue resistance in duct work and this is
only valid on a system that is already clean. Once you know that the system is set up for proper
settings, measure the total external static, supply static on positive side and the return static on
the negative side. And whichever one has higher number , is the side you need to look at, like
looking for kinked ductwork or improperly strapped ductwork or undersized ductwork. There
are a lot of things that can go wrong with the ductwork. Once you were done with this proceed
to step 6.
Step 6: Check the refrigerant pressures and temperatures. There is a wide range of pressures
and temperatures but the is not the video about but you want to check your sub cooling,
superheat, suction saturation, liquid saturation. Tip, you can use an app called measureQuick to
make it easy for you and see of you are in range.
Step 7: Confirm that you don’t have any restrictions like temperature drop, across liquid line
filter dryer, those are the types of things you need to ensure that you do not have and also
check if the metering device is operating properly that its not underfeeding the evaporator coil.
A lot of people say that the Charge problem or restriction in liquid line won’t cause freezing
but it depends on run time, the market and the amount of moisture is in the air. But there are
certain cases where restrictions whether its underfeeding metering device or restrictive liquid
line dryer or a system that is undercharged can cause freeze-ups on an evaporative coil so pay
attention to that. In terms of liquid line filter dryers, you may want to use the same clamp on
either side of the liquid line filter dryer and make sure that you do not have pressure drop
across that liquid line filter dryer. Anything that is measurable over 1 degree is an indication of
a restriction in most applications.
Step 8: Confirm all refrigeration cycle components and the processes are functioning properly.
Because there are a lot of things that can go wrong depending on the type of system you’re
working on and anything that causes the evaporator temperature to drop below 32 degrees,
thats what causes a freezing evaporator coil. So you have to understand about suction
saturation and know that your system is properly matched. Because if the size of evaporator
coil does not matched up the condensing unit, it can cause a problem. There are lot of reasons
that can cause it, so you have to make sure that everything is what its supposed to be. Again
When you start earlier in the process and just go with most obvious things, many times you’ll
fond obvious problem early.
Step 9: Lastly, make sure that you have the proper refrigerant charge. This is where you check
the superheat, sub cool, suction saturation, liquid saturation, condensing temperature over
ambient, design temperature differences on evaporator coil.
Before starting with anything, always start first with the airflow. Because it is one of the largest
cause of coil freezing, especially consistent coil freezing getting the airflow settings wrong,
having a mismatched system, ductwork is too small, dirty blower wheel, dirty filter, these things
are the things you need to pay attention first. Because if you don’t have proper airflow over the
evaporator coil then the evaporator coil is going to run colder and it will be prone to freezing.
But before doing anything, read the manual first of the equipment you are going to work on
and you have to have proper knowledge of what the proper airflow should be in order to know
whether or not you hit that target.
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