Updated: Feb 23
EPA 608 Core Chapter 35(Take full course for free)
In this module, we will take a look at the term dehydration and its affects the HVAC systems.
1. Dehydration Definition
Recall from our module on Refrigerant Oils that oils can react with water to create toxic and corrosive acids. This will cause major system failures. So we do not want water or water vapor in the system.
Dehydration is the process of removing water and water vapor from the system. We dehydrate the system by evacuating it.
The recommended method to dehydrate a system is to evacuate it. Evacuation is when we remove all water vapor and air from the system.
A system is considered dehydrated when you have reached and held a vacuum of 500 microns or less.
If the system contains a hermetic compressor, you need to make sure it is not operating when you pull a dehydration vacuum. If the hermetic compressor is operating, it will prevent you from pulling a deep vacuum.
So basically, in addition to removing all the water vapor from a system, evacuation includes removing all the air from the system as well.
So to reiterate, evacuation is the best method for dehydrating a system. We also need to evacuate a system before any major system repairs.
To remove all the air and water vapor from the system, we need to use a vacuum pump to pull a vacuum on our system.
To pull a vacuum, we need to make sure that the vacuum pump is capable of pulling a deep vacuum. We define a deep vacuum to be 500 microns.
Vacuum lines or hoses need to be equal to or larger than the pump intake connection. If the mouth of the hose is smaller, you would not be able to pull a vacuum.
The piping connection to the vacuum pump should be:
As short in length as possible, and
As large in diameter as possible
To measure the final system vacuum,
Isolate the system,
Turn off the vacuum pump, then
Measure the final system vacuum
To measure correctly, we need to attach the
Vacuum Gauge to the high side, and
Vacuum Pump to the low side
Over-evacuation of a system does not occur. Recall that the purpose of evacuation is to remove all air and water from the system.
You cannot remove too much air and water from the system because you want all of it to be gone. If you evacuate past the point that is necessary, this will not damage refrigeration line sets. This is because they are made of metal such as copper, aluminum, or steel.
You have reached dehydration when the vacuum indicator shows you have reached and held a vacuum of 500 microns or less.
3. Factors Affecting Dehydration Time
Dehydrating time is the time it takes to remove all water and water vapor from a system. Recall that dehydrating is done by evacuating a system, which involves removing air and water from the system.
We generally want to minimize the amount of time spend dehydrating a system. The longer we spend dehydrating, the larger the risk of any component failing in the system. Your time as a technician is also valuable.
That being said, we need to make sure we are taking safe measures to decrease our dehydration time. Safety is always number one.
The following factors contribute to a system’s dehydration time:
Amount of Moisture
Vacuum Capacity, and
Suction Line Size
The larger the equipment, the longer it will take to dehydrate it. This is simply because there is more work to do. Imagine mowing a lawn. The bigger the lawn, the more time it takes to get the job done.
The ambient temperature is the temperature of the system. The colder it is or the lower the ambient temperature, the more time it’s going to take to dehydrate.
That’s why we want to heat up the system to decrease the dehydration time. The higher the temperature, the less time it will take to dehydrate. We can use a heat blanket to heat the system safely.
Recall that we never use a flame to heat up the system. We are working with possibly flammable materials that operate on high pressure. Using an open flame can lead to explosions.
The more moisture there is in the system, the longer it will take the dehydrate the system. Going back to the lawn mowing scenario, the mount of moisture would be like the amount of overgrown grass in your lawn. The more grass you have, the longer it will take to mow.
And lastly, the vacuum capacity is the rate at which your vacuum can pull out moisture and air. The smaller your vacuum capacity, the longer it will take to dehydrate the system. The smaller your lawn mower, the longer it takes to mow the lawn.
The longer the suction line, the longer it will take a dehydrate a system. That’s why we want to keep the suction line as short as possible.
In this module, we defined the term dehydration and discussed the factors affecting dehydration time.