Checking the Refrigerant Charge in the Colder Months! Recently I received this message from one of my YouTube subscribers. This was a great question and I thought I would share.
Mr. Walker thank you for your great videos, I was wondering if you made any videos about checking subcool and super heat in the colder months, I live in Florida so the lowest temp here is about 30 degrees, so I guess my question is can it be done at low temps and get a accurate reading? If not what do you feel is the lowest temp you can be at to get an accurate reading? I hear many different things at my job, I would like hear you answer. I have been a field tech for 2 years an dedicate my spare time to always gain more knowledge, and your videos are by far the best for me to learn from.
Thank you for your time and support
J in Florida
J, thanks for the great question.
As a troubleshooting tool, subcooling can be checked when outdoor temps fall below the range of the manufacturer's subcooling charts. I routinely use subcooling to check the system charge because dirty coils, dirty filters, bad metering devices, outdoor temps don't have much of an impact on subcooling. In the summer months, I do check to superheat to verify proper metering device operation, airflow, and the overall evaporator performance.
Quick review:
- Subcooling levels are determined by the amount of refrigerant in the system.
- The length of time the refrigerant spends in the condenser determines the subcooling level.
- If there is too little refrigerant, it shoots through the condenser, spending very little time becoming subcooled. When this happens, there is little to no subcooling.
- Too much refrigerant causes a back-up of refrigerant in the condenser and the refrigerant spends too much time in the condenser getting subcooled. When this happens subcooling is higher than normal
Cold weather subcooling test.
- Crank the heat up in the home to produce some heat load for the evaporator. 75F to 76F or so.
- Switch the system into the cooling mode.
- Use cardboard or a tarp to block the airflow through the condensing unit.
- This raises the high side saturation temperature and pressure.
- Watch your high side gauge. When it reaches 105F to 110F, make sure it is holding steady- this takes a bit of adjustment of the tarp or cardboard but doesn't take too long.
- You can now check your subcooling levels as you normally would.
This procedure will give you a fairly accurate subcooling measurement in the colder months. Of course, accurately charging the system can only be accomplished by using the manufacturer's charging charts.
Here's a short video on how to check subcooling -
Watch the archived video on YouTube
by Ron Walker