MO99

I was wondering about you guys experiences with MO99. I am going to have to start this season using it and have no experience with it.

Awesome question, particularly with the cost of R-22 continuing to go through the roof.

The most important part of any of the retrofit refrigerants (a refrigerant used in place of the OEM system desired refrigerant) is that they should be charged properly. This means they are to be added using one of 3 methods: Using either Superheat, Subcool or the Weigh in method of determining the correct amount of refrigerant. This includes the need to clean the coils and verify proper airflow before installing it, or any refrigerant for that matter into a system.

Since MO99 (R438) and many other refrigerants are not a complete blends they must leave the jug in a liquid state meaning the jug must be upside down. A charging adapter should then be used to ensure it is a vapor before getting to the compressor.

Operationally, I've seen it both increase and decrease capacity in a system. (Although to be honest that probably has more to do with how well the coil was cleaned and accurate the charge is than the specific refrigerant in use.) It is best to stick with a refrigerant once started as an alternate on a community as they are not to be mixed. (NEVER MIX ANY REFRIGERANT IN A SYSTEM.) This can be dangerous. In other words, if your community is going to stick with the R22 equipment, don't have some on your property be MO99, others R421, still more R407c etc... That situation can turn into a logistical and bookkeeping nightmare!

What type of charging adapter? Also is it always necessary to install a filter/dryer? My concern is that I have a 8 year old property that is 99.9 %R22 and a simple job that would take 30 minutes turns into 2 hours now.

The charging adapter I have is sold through various suppliers and is called an "Insta Charge" fitting. Essentially it's a metering device that is threaded (1/4inch flair) to fit between the manifold and low side hose in line to allow the refrigerant to change state. Alternatively it can be installed directly on the refrigerant tank. (I have a problem remembering to remove it from there and have lost a couple that way...)

In truth the refrigerant should require no extra time to use as all of the procedures are the same as proper use of R22. The only difference is the exception of flipping the jug. This means that as long as R22 is currently being used correctly, it's the same time frame for repairs.

Filter dryers are a strong recommendation on all systems now. I want them on all the one's that I service as new compressors contain POE oil that doesn't give up all of the moisture they collect during service, even in a deep vacuum. When changing a system from R22 to MO99, manufacturer recommendation is to replace any filter dryer, and charge as needed. (According to them, flushing a system is not required unless the system is contaminated due to burn out.)

I have used MO99 on several of our units and have had great results. Everything I have read says no substitute for R22 will measure up but so far I am not seeing that. I have noticed that MO99 has gone up around the North West Arkansas about $100 from this time last year.

Paul -- You are mostly correct in your comment that there are normally three methods for determining if a unit is charged properly: superheat, sub-cooling, and the weigh-in method. However, a tech must remember that the thermal expansion valve (TXV) used as a metering device on the indoor coil of most heat pump systems makes charging a system using the superheat method impossible. The TXV valve is designed to "adjust" the amount of refrigerant that passes through it to maintain the superheat within its operating range. If we use it as our measure of what will be the correct charge, we will be unsuccessful because it will continue to adjust for the amount of refrigerant charge regardless of whether too much or too little refrigerant is being used. In this case, the thing that makes a TXV a good metering device for refrigerant (its ability to self adjust for a slight over or undercharge of refrigerant), is also the thing that makes it an unsuitable choice for heat pumps using a TXV on the indoor AHU.

Happy afternoon David,

You are correct in the method of determining proper amount is specific to the system design:

---Superheat is used for fixed orifice metering device systems
---Subcool charging is used for systems that have a variable metering device (TXV or TEV)
---Weigh in charging is the most accurate and is used in systems that the line-set is a known distance (Hermetic systems such as room units, water source heat pumps or PTAC).

The reason for my comment saying that the only 3 acceptable methods is intended as an attempt to battle the most common mistakes made when using any refrigerant. These wrong ways are commonly referred to as "adding it till the low side is Beer Can Cold", or "charge it to a specific psi".

When using a refrigerant, like MO99, on a system that was designed for a different refrigerant (R22) the system is already changing from what the manufacturer intended. If it's charged incorrectly it makes the situation even more challenging.

Have fun!