HVAC KNOW IT ALL | May 05, 2018 | Categories: Refrigerant , Refrigerant Recovery
I often see new techs asking how to recover or experienced techs asking how to recover faster, so let’s take a look at both. If looking to connect with a strong culture of HVAC technicians, check out the subscription-based HVAC Know It All app.
This all originated from some personal trial and error when an air conditioning manufacturer I worked for had a recall, a missing Schrader core at the receiver service valve (king valve) of all things. This was a possible disaster for an unsuspecting tech. Remove the cap expecting a valve core, and well... Not fun. So it was time to install a single valve core in 50 operational units in critical spaces, each holding between 50 and 100 pounds of R-410A.
I had a reasonably repeatable situation on my hands, and I had the opportunity to try all sorts of things: recovery cylinder size, hose size, hose type, etc. I’ll cover all this at the bottom of this article, but we’ve got to start with the basics!
How do we recover?
There are two typical methods, direct recovery and push/pull. You should always familiarize yourself with the equipment you are working with, but I’ve included a simple diagram of how to connect the required equipment and a “step-by-step” guide for the newer techs.
Direct Recovery
This is our typical recovery method, which will be how every recovery task will finish.
1. Start with all valves closed (recovery cylinder, recovery machine, manifold, hoses.)
2. Setup hoses as shown in the diagram.
3. ZERO/TARE the refrigerant scale.
4. Open hose valves, core removal tool valves or service valves.
1. ---The below steps will vary with your recovery machine---
5. Set the refrigerant recovery machine to recover.
6. Open the high side of the manifold for liquid recovery.
7. PURGE THE HOSES OF AIR, loosen and unseat the hose connected to the recovery tank until the refrigerant is present, and then retighten.
8. Fully open the vapor valve on the recovery cylinder.
9. Turn on the recovery machine.
2. ---The below steps should be standard for most recovery machines---
10. The manifold high side valve may need to be adjusted to throttle refrigerant flow into the refrigerant recovery machine to avoid liquid slugging.
11. When the liquid recovery is complete, fully open both the high side and low side manifold valves.
12. Many recovery machines will turn off once the system reaches a vacuum.
13. PURGE THE RECOVERY MACHINE – this one can be pretty specific – so check your manual if you’re unsure.
14. Close all valves and recovery is complete!
Push/Pull
This will be your faster option if the system has 15 or more pounds of refrigerant. The more refrigerant the system holds, the more time you’ll save. Tip: Using an inline sight glass during push-pull recovery will allow you to visually determine when the liquid flow has stopped.
1. Start with all valves closed (recovery cylinder, recovery machine, manifold, hoses.)
2. Setup hoses as shown in the diagram.
3. ZERO/TARE the refrigerant scale.
4. Set the recovery machine to recover.
5. PURGE THE HOSES OF AIR (this is done slightly differently than in direct recovery.)
a. Open the liquid line service valve or core tool and then loosen and unseat the hose connected to the liquid port on the recovery tank until the refrigerant is present and then retighten.
b. Open the vapor line service valve or core tool and then loosen and unseat the hose connected to the vapor port on the recovery tank until the refrigerant is present and then retighten.
6. Turn on the recovery machine.
7. When liquid recovery is complete, switch to Direct Vapor Recovery.
Now, let’s speed it up...
Valve Core Removal Tools
• If you were only going to change one thing – this is it! If you’re stuck pulling through valve cores, get two of these. They’ll even help speed up your evacuation.
Recovery Cylinder
• Make sure the cylinder is clean and has been evacuated to 500 microns or less. And NEVER fill beyond 80%. This allows for the expansion of the refrigerant.
• If it’s practical, use a larger cylinder; this will make the recovery go quicker.
Hoses
• Avoid hoses with “anti-blowback” or “low loss” style fittings. • Standard hoses are ¼” – using larger diameter hoses will get you faster recovery. They’re often marketed as “heavy duty,” “charging,” or “vacuum” hoses.
• Use hoses that are as short as possible.
Temperature
• Cool down the recovery cylinder– this will drop the pressure of the recovery cylinder. • With many recovery machines, you can use the fan to draw air over the recovery tank.
• Water will work even better, but you’ll need water flow.
• Cool down the refrigerant! This one tends to be your best bet if you’re dealing with large volumes of refrigerant – there are heat exchangers available for just for this purpose.
Filter It!
• If you suspect the system refrigerant to be dirty, use an inline filter drier at the inlet to the recovery machine.
With methods ranging from nothing new required to a whole new rig for recovery, you’ve got choices to speed up your recovery in just about all applications. Give some of these a try and see how they work for you.
Dan Reggi
Humber College Professor
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Testing with soap bubbles is used:
to pinpoint refrigerant leaks
Many refrigeration units use an open compressor. Which part of the compressor is most likely to leak if a unit is not used for several months?
When a new system has been assembled (built-up), and is ready for testing, the first thing to do is:
Pressureize with an inert gas and leak check
EPA regulations require that all appliances containing more than 50 pounds of refrigerant, except commercial and industrial process refrigeration, be repaired when the leak rate exceed what percent of the charge per year?
When using recovery and recycling equipment manufactured AFTER 11/15/1993, techs must evacuate an appliance component containing more than 200 pounds of CFC-12 to the following level before making a major repair:
Appliances containing CFC refrigerants can be evacuated to atmospheric pressure when:
Leaks in the appliance make evacuation to the prescribed level unattainable
When using recovery and recycling equipment manufactured BEFORE 11/15/1993, techs must evacuate an appliance component containing 10 pounds of CFC-500 to the following level before disposing of the appliance:
What repairs are designated as major repairs under EPA regulations?
Replacement of the compressor, condenser, evaporator, or the auxillary heat transfer coils
System-dependent recovery equipment CANNOT be used when?
The appliance contains over 15 pounds of refrigerant
You are changing out the compressor of a system containing 40 pounds CFC-502. Your recycling equipment was manufactured AFTER 11/15/1993. In addition to isolating the compressor as much as possible, what else should you do?
Evacuate the isolated section of the system to 10 inches of vacuum hold. If system pressure does not rise, remove the compressor
Refrigerant has been recovered from an AC system and held in a refillable cylinder, in order to replace the condenser coil. The refrigerant can:
likely be charged back into the system
What else can recovered refrigerant contain?
Recovering refrigerant from a system in vapor phase will minimize loss of:
With an air-cooled condenser on the roof of a building and the evaporator on the first floor, recovery should first occur:
From the liquid line entering the evaporator
In general, what is one routine maintenance task which must be performed on most refrigerant recycling machines?
After refrigerant liquid has been recovered from the appliance, any remaining vapor is:
Condensed by the recovery system
Refrigerant should be removed from the condenser outlet when:
The condenser is below the receiver
What should be done before transferring refrigerant to an empty cylinder?
Cylinder should be evacuated
During evacuation with large amounts of moisture it may be necessary to increase pressure to counteract freezing with gas such as:
Liquid charging of a CFC-12 refrigeration system with risk of freezing is begun with vapor from a vacuum level to a pressure of approximately:
Noncondensibles in a refrigerant system result in:
Higher discharge pressure (head pressure)
The component directly following the evaporator of a refrigeration system is the:
A moisture-indicating sight glass is useful for:
Checking the refrigerant's moisture content
Dry nitrogen should be used to break the first vacuum when dehydrating by the double evacuation method. However, the cylinder must use:
What should be used to leak in an HFC-134a system for leak checking?
A refrigerant oil that is hygroscopic:
The term used to describe the fact that a refrigerant blend has a range of boiling or condensing points at a constant pressure is:
When recovering refrigerant, what should be done to the High-pressure system before recovery?
System must be turned off and remain so, and as much as is possible, all solenoid valves should be open.
What side is the receiver on in a High-pressure system?
High-pressure systems have a tendency to "load up" on moisture when opened. What must be done every time these systems are opened?
Change the filter-drier on the liquid line.
What are the 3 positions of a King Valve?
1. Refrigerant flow through main line and service gauge. 2. Refrigerant flow through the main line only (backseated). 3. All ports closed.
What is the result of an undercharged system due to leaks?
What is one benefit each of recovering in the liquid phase and recovering in the vapor phase?
Liquid: faster recovery. Vapor: minimize loss of oil.
When using a recovery machine for a different refrigerant, what steps should be performed first?
1. Oil must be drained and replaced with new oil for refrigerant. 2. All filters must be replaced. 3. Unit must be evacuated with another recovery machine or a "pump-out" cycle.
What should be done to the recovery tank during recovery?
What state must the appliance be in for recovery?