Microchannel Unit Charging

As many of you know, we are using a condenser coil design called MICROCHANNEL in both commercial and residential. cooling products. With this technology, we have been able to decrease our equipment size while maximizing our SEER ratings on our equipment.  It is a great benefit to all.

One of the best features of our microchannel units is the smaller size of the unit, which is made possible by the size of the microchannel condenser coil used in each unit. This smaller sized condenser coil results in a refrigeration system that requires less refrigerant than a comparable unit with a tube-and-fin condenser coil. The amount of factory charge is up to 50% less than tube-and-fin units.

Because of the unique design of these coils and the fact that they use about half of the refrigerant needed for conventional “tube and fin” coils, charging of these units is critical.  It is very easy to overcharge a unit with a microchannel coil.  The flow through these coils is what is referred to as “parallel flow”, which means in the top portion of the coil, all the refrigerant flows in 1 direction to de-superheat  the refrigerant  and then enters into a header where it drops down to the bottom part of the coil where the refrigerant is subcooled providing a solid column of liquid refrigerant so the metering device can function properly.

The coil is made out of “tubes” that contain “microchannels”

and it is through these microchannels that the refrigerant flows.

So, now that you understand microchannel technology, you can see that the microchannels are quite small accounting for the lower refrigerant charge in these units. The significance of this information is that a microchannel condenser coil has less volume and cannot hold as much refrigerant as the old style tube and fin design.

The recommended procedures for charging a unit with a microchannel coil are:

1) On any NEW INSTALLATION, accurately measure the length of the correctly sized line set.

2) weigh in the charge based on coil and line set adders published in the Tabular Data sheet for the unit you are installing.

3) allow system to operate at least 15 to 20 minutes for charge to stabilize. Anytime you add or remove refrigerant, it is critical to allow this time for the refrigerant to circulate and stabilize in the system before adding or removing more refrigerant.

4) check head pressure per charging chart on unit. All residential units have this chart on the side of the unit near the data plate.

5) check superheat (for indoor orifice metering device) or subcooling (for indoor TXV metering device). This information is also on the side of the unit by the data plate.

6) When in doubt, verify operation of system per the information in the Service/Condenser Application Guide (438317-UAG-B-0409) available through your local branch.

If these procedures are followed, proper charging of a microchannel unit can be accomplished without overcharging a unit. 

One other thing of significance to note:

HVAC technicians are tempted to pump down a system that has a microchannel condenser coil. This practice can result in damage to the compressor or condenser coil. Therefore, THE PUMP DOWN OF REFRIGERANT INTO A MICROCHANNEL UNIT IS NOT APPROVED UNDER ANY CIRCUMSTANCE.

Hopefully, this information will be helpful to you and your service personnel.

One last thing, the microchannel coil can be repaired.  We have a kit for repairing a leak in the aluminum coil.  We also have a video showing how to do it.  Contact me and I’ll be glad to send you a copy of the video via email.