Guide to Refrigerant Charging Procedure Details
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Refrigerant charging procedures for air conditioners, heat pumps, refrigeration equipment using a test gauge set and charging cylinder or scale
Procedure for evacuating or "pulling a vacuum" on air conditioners & heat pumps or refrigeration equipment
Procedure for Charging the HVAC System or Appliance with Refrigerant Using a Gauge Set
Current refrigeration service standards including charging precision and refrigerant recovery
Procedure for filling & using a refrigerant charging cylinder, Robinair® example
Procedure for using a vaporizing connector for low-side refrigerant charging, Kwik-Charge™ example
Questions & Answers about refrigerant charging of air conditioners, heat pumps, refrigeration equipment

Adding or replacing the refrigerant: this article describes the procedures for charging an air conditioner, heat pump, refrigerator, freezer, or similar equipment - how does an HVAC service tech put the proper amount of refrigerant into the system? We describe use of a traditional charging cylinder, vaporizing connectors for low-side charging, and modern refrigerant recovery, charging, and vacuum equipment.

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Procedure for Charging the HVAC System or Appliance with Refrigerant Using a Gauge Set

Also see GAUGE, REFRIGERATION PRESSURE TEST and see REFRIGERANT PRESSURE READINGS. Readers whose air conditioners or heat pumps are not working properly should see LOST COOLING CAPACITY, also see REFRIGERANT LEAK REPAIR at our discussion of REFRIGERANTS under AIR CONDITIONING & HEAT PUMP SYSTEMS.

Evacuating The Refrigeration System Before Charging

As we've explained, charging an empty system will require evacuating it first. For a typical household equipment this takes about 15 minutes but for a larger commercial refrigeration system this process can take an hour.

On residential equipment we always leave our evacuator pump running for at least 1/2 hour to be sure we've evacuated as much moisture and contaminants as possible.

On commercial systems being installed or having major service it would be preferable to leave the evacuator pump running for 12 hours - the longer you evacuate the system the cleaner it will be. That's because as the system warms up moisture in the system will vaporize further and thus be removed.

R-22 refrigerant and air conditioning test gauges (C) Daniel Friedman

Low Side Refrigerant Charging

Low side charging is also referred to as vapor charging - that is we allow ONLY refrigerant vapor or gas to enter the system.

This is an easy but time consuming method of system charging. The canister supplying refrigerant is connected to the gauge service port and opened, and the HVAC equipment or appliance is run (which pumps refrigerant gas from the supply source in parallel with pumping from the outlet of the evaporator coil).

The refrigerant canister is kept upright so that only gas leaves the canister.

High Side Refrigerant Charging

When charging an air conditioner, heat pump, or refrigeration appliance from the high side, the system being serviced is turned OFF. The refrigerant gas canister is placed upside down so that only pure liquid refrigerant leaves the canister.

Note that once you start the system running you will not be able to charge on the high side because the head pressure out of the compressor will be higher than the evaporation pressure in the canister - it would push refrigerant back into the canister.

Methods for Measuring a Refrigerant Charge

With critically-charged HVAC or appliance refrigeration systems, such as a household refrigerator or air conditioner, you must measure the refrigerant entering the system. Typically the technician uses a scale that registers in ounces to measure a weighed charge, though we also used other devices such as a charging cylinder that actually shows the volume of liquid refrigerant in the cylinder on a temperature-compensating scale.

A charging board (or charging cylinder just mentioned) that is connected to the high side can accurately measure the liquid refrigerant charge going into the system. In this case the charging board (Dial-a-Charge charging cylinder produced by Robinaire, Montpelier OH) is loaded with the proper refrigerant charge from the gas cylinder, and the outlet from the charging board is then connected into the high side (perhaps through the gauge service port).

A Vaporizing Connector is an accessory you can add to a charging cylinder or charging board. The refrigerant vaporizing connector (such as Imperial's Kwik-Charge, assures that liquid refrigerant passing through the device will convert to gas as it exits the device. This will let you add a measured refrigerant charge to the low side of the system while still making an accurate measurement of the refrigerant measured in ounces.

Liquid refrigerant charging is always faster than low side vapor charging. On the low side you have to charge, then wait for the system pressures to balance, then reexamine the frost line etc.

An alternative to measuring the refrigerant charge when charging air conditioners or heat pumps

As an alternative to making refrigerant measurements by weight or temperature-corrected volume using a scale or charging cylinder, some HVAC service technicians may adjust the refrigerant charge by watching the low side pressure and the exact location of the frost line at the evaporator coil (blower fan not running).

Watch out: do not overcharge or extend the frost line to the compressor or you risk sending liquid refrigerant into the compressor motor - assuring its damage or destruction.

Guessing at Refrigerant Charge Level

On small refrigeration systems such as a home refrigerator or window air conditioner the refrigerant charge needs to be accurately measured or the system will not work properly. But on larger HVACR systems and on commercial units that use a liquid refrigerant receiver (a sort of buffer that stores extra liquid refrigerant), you might find a sight glass on the refrigerant piping downstream from the condensing coil.

Some techs add refrigerant while watching that sight glass, adding refrigerant untilt the gas bubbles just stop. If you see bubbles there either the system is badly contaminated or more likely the refrigerant charge is short. We warned just above - don't overcharge the system - you can damage the equipment.

Pulling a vacuum to evacuate refrigeration systems

Note that a reading of "zero" on these pressure gauges is not really zero, it's 14 psi or 1 atmosphere.

Also if you look closely at your gauges you 'll see that one permits pressure readings in the "negative" direction - used when pulling a vacuum on the system using an evacuator pump - a step necessary before charging a system that has been opened for service or repair.

To remove all moisture or refrigerant from an air conditioner, heat pump, refrigerator, or other refrigeration equipment your evacuator pump needs therefore to pump past "zero" on the gauge (14 psi) to absolute zero or 29.9" Hg vacuum.

The evacuator pump is attached to the center port or "service port" on the gauge set.

Using a Refrigerant Charging Cylinder - Robinair® examples

Current refrigeration service standards

SAE J-2788, requires that all service equipment manufactured after December 31, 2007, must recover 95% of the refrigerant and recharge to within 1/2 ounce.

Charging cylinders such as the 1980's vintage equipment described below are often supplanted now (2011) by refrigerant charging scales and by larger, more sophisticated refrigerant charging machines that combine refrigerant charge measurement, refrigerant evacuation and recovery/recycling, and other service functions.

Newer refrigeration service equipment can automatically recover refrigerant (such as R134A) from a system to be serviced, vacuum test and clean the system to prepare it for a charge, leak test the system, and insert the proper refrigerant charge, all automatically.

These improved refrigeration management functions were required by a combination of legislation and standards that stop the discharge of refrigerants into the environment, and by improvements in refrigeration system design that produced equipment that uses a smaller, but more precisely-measured charge of refrigerant.

Quoting from Robinair's description of their current refrigerant management equipment line:

Robinair 34988, 34788 & 34288 recover up to 20% more refrigerant, which means it will cost less to recharge the system. The best charge accuracy that could be claimed by older generation service machines was +/- 1 ounce, a 3% error on a two-pound system. That same charge accuracy on a 14-ounce system is over twice the error (7%). Early R-134a systems could still provide some cabin cooling when they were 4-6 ounces (12-18%) low on refrigerant. However, new designs are so efficient, they do not have reserve refrigerant, and charge accuracy is critical. The 34988, 34788 & 34288 will recharge the vehicle to within 1/2 ounce of the charge capacity, and you will avoid the dreaded “come back”. [1]

How traditional Charging Cylinder Worked to Put a Measured Refrigerant Charge into Refrigeration Equipment

While the new refrigeration system testing and charging equipment described above is fully automatic, to understand the problems that the newer equipment has to solve (and automate), it is useful to review how, traditionally, we inserted a precisely measured refrigerant charge into air conditioners and other refrigeration equipment.

We used the Robinair® Dial-a-Charge® charging cylinder for many years as a way to install an accurate charge of refrigerant into air conditioners, heat pumps, and refrigerators and freezers undergoing service or repair. As an aid to service technicians who may have lost their instruction sheet we include and comment on the charging cylinder instructions here, using the Robinaire® Dial-a-Charge charging cylinder system as an example.

Robinair offered the following explanation of charging cylinder use along with our 1980's vintage equipment.

With an increase in temperature in any cylinder filled with refrigerant, there is a corresponding increase in pressure and a change in the volume of liquid refrigerant in the cylinder. To measure out an accurate charge by weight from a cylinder using the liquid level in a sight glass as a point of measurement, it is absolutely necessary to compensate for liquid volume variations caused by temperature variations. These temperature variations are directly related to pressure variations and accurate measurements by weight can be calibrated in relation to pressure.

The Dial-a-Charge Charging Cylinder is designed to meter out a desired amount of a specific refrigerant by weight. Compensation for temperature variations is accomplished by reading the pressure on the gauge of the cylinder and dialing the plastic shroud, with the calibrated chart, to the corresponding pressure reading for the refrigerant being used.

When charging a refrigeration or air-conditioning system with refrigerant, often the pressure in the system reaches a point where it is equal to the pressure in the [charging] cylinder from which the system is being charged. In order to get more refrigerant into the system to complete the charge, heat must be applied to the cylinder.

Robinair's Heated Dial-a-Charge Charging Cylinder eliminates the problem caused by equalization of pressure between the cylinder and the system being charged. The [Robinaire] charging cylinder has a heating element installed in the base of the cylinder. The male plug of the heating element can be plugged into any 110-115 volt AC outlet. [Note that if you want to charge the system on the low side using vapor only, you can safely do so using a refrigerant vaporizer attachment instead of heat to assure that no liquid goes where it's not wanted.]

Due to the variety of 220V. receptacles throughout the world, a male plug must be field-added to the 220V heating element in order to fit the particular style in your area [outside the U.S., Canada, Mexico]. Either voltage heating element will work on 50 or 60 Hz power.

Watch out: CAUTION: Heating elements can be destroyed if plugged into an electrical outlet when the [charging] cylinder is empty [of refrigerant].

The heating element is of the correct wattage to increase [refrigerant] pressure sufficiently in a relatively short time, to a level that is above the equalization pressure between the cylinder and the system [being charged]. The higher the pressure in the cylinder, the less time it takes to force the refrigerant into the system.

The heating element should be turned off before the pressure is above the highest pressure on the Dial-a-Charge® shroud of the refrigerant being used. EXAMPLE: Refrigerant R22 is being used - the pressure at no time should exceed 230 psi.

The Robinair Dial-a-Charge® has a relief valve, for added protection, set to relieve the refrigerant at approximately 320 psi.

- [1]

Procedure for Filling & Using a Refrigerant Charging Cylinder

Watch out: CAUTION: When working with refrigerants, goggles should always be worn. Contact with refrigerants may cause injury.

Connect the charging hose from valve at bottom of charging cylinder to valve on refrigerant supply tank. Invert refrigerant tank so the valve is down. IN this position, liquid refrigerant will flow from the tank [into the charging cylinder when the valves are opened].
Open the bottom valve on the charging cylinder and the valve on the refrigerant tank. When the liquid refrigerant appears in the sight glass, observe the pressure on the gauge at the top of the cylinder. Dial plastic shroud to column where its pressure heading for the refrigerant being used corresponds with the gauge pressure and is in line with the sight glass.

EXAMPLE: if the pressure on the gauge at the top of the [charging] cylinder reads 70 psi, find the column with the pressure heading of "70" and line this column up with the sight glass.

NOTE: On models which are calibrated for various types of refrigerants, be certain that the pressure heading corresponds to the refrigerant being used. Located at the bottom of the plastic shroud are the listings of types of refrigerant.
When the pressure in the cylinder equalizes with the pressure in the tank [of refrigerant], th refrigerant will stop rising in the sight glass. At this point, intermittently, open the valve at the top of the cylinder to relieve head pressure. This will allow refrigerant to continue filling the cylinder.
When refrigerant reaches the desired level in the sight glass [ this is the precise measured refrigerant quantity with which you want to charge the system], close the valve on the refrigerant tank and then the valve on the charging cylinder. Be certain that the valve at the top of the cylinder is fully closed.
Connect the heating element to the proper voltage source to allow the refrigerant to heat and build up pressure. This pressure build-up will allow the pressure of the cylinder to be higher than that of the [refrigeration] system [being charged] and force the refrigerant into the system. [Note that when charging a refrigeration system on the low side it will be easier to insert the refrigerant charge because you're not fighting head pressure].
Re-dial the plastic shroud to match the [charging cylinder] gauge pressure whenever a pressure change occurs.

- [1]

Using a Refrigerant Vaporizing Connector for Low-Side Refrigerant Charging: Imperial Kwik-Charge as example

As we introduced above at Measuring the Refrigerant Charge, a vaporizing connector is an accessory connected to the refrigerant canister, refrigerant gauge set, to a charging cylinder or charging board to provide a safe, fast way of low-side refrigerant charging without any risk of slugging the air conditioning compressor with liquid refrigerant - an event likely to damage the compressor.

The refrigerant vaporizing connector (such as Imperial's Kwik-Charge illustrated here), converts liquid refrigerant to a gas as the refrigerant flows through the vaporizing device, thus making sure that liquid refrigerant passing through the device will convert to gas as it exits the device. This will let you add a measured refrigerant charge to the low side of the system while still making an accurate measurement of the refrigerant measured in ounces.

Vaporizing Connector Description

[Quoting and paraphrasing][3], Using the Kwik-Charge™ vaporizing connector provides a safest, faster method of charging fluorinated hydrocarbon refrigerants into the low pressure side of a refrigeration system.

Vapor charging is also within the capacity of this unit, although it is primarily intended for liquid charging - that is, liquid refrigerant is fed into the vaporizing connector, and only refrigerant vapor exits the device.

The Kwik-Charge™ vaporizing connector may remain attached to the low-side port of the charging manifold while performing the usual refrigeration equipment service and diagnostic operations involved in maintaining a refrigeration system, such as pulling a vacuum to clean the system and test it for leaks.

An automatic bypass valve inside of the vaporizing connector permits full flow during any reverse-cycle operation such as pulling a vacuum or removing refrigerant that is already in the system.

As an example for technicians unfamiliar with vaporizing connectors we quote from the Kwik Charge instructions for the device we illustrate here. [3]

Advantages of using a vaporizing connector for low-side charging of air conditioning, heat pump, and other refrigeration systems

[Quoting and paraphrasing][3],

This device provides fast, safe refrigerant charging when using tracing dye [or not] with these properties:

Up to eight times faster refrigerant charge insertion than when using unassisted vapor charging
No pressure drop in the charging cylinder (avoids chilling and speeds the charging process)
No need to heat the refrigerant charging cylinder
One charger services both large and small HVAC systems and refrigeration equipment
Built-in check valve opens for drawing unrestricted vacuum - this means you don't need to remove the vaporizer to pull a test vacuum on the equipment
Can be used with all fluorinated hydrocarbon refrigerant systems

Instructions for using the Kwik Charge liquid low-side charger for air conditioning and refrigeration systems

The Kwik-Charge may be used with a charging manifold, a calibrated charging cylinder, or with any other charging equipment. Installation can be made by any of the methods illustrated [see sketch above]. After installing the vaporizing attachment, connect all hoses as usual
When pulling a vacuum, do so in the normal manner. The vacuum will activate the automatic bypass inside the Kwik-Charge and provide a full flow path for rapid evacuation of the HVAC system or refrigeration appliance
Isolate the refrigeration unit from the vacuum pump after the desired degree of evacuation has been reached. Then slightly pressurize the system with refrigerant vapor (approximately to 5 psi).
Put the refrigeration system into operation - this means the compressor should begin running.
With the system running, proceed to charge the refrigeration unit - by opening the refrigerant supply valve to meter refrigerant out of the measured charge device, passing refrigerant through the vaporizing attachment and into the low-side of the air conditioner, heat pump, refrigerator or other appliance being charged.
Charge each system according to the system manufacturer's recommendation

Watch out: CAUTION: a minimum hose length of three feet should be maintained between the Kwik-Charge and the low side charging port on the refrigeration system. Be sure to observe all safety practices regarding handling of refrigerants, including the wearing of eye protection.

Questions & Answers about refrigerant charging of air conditioners, heat pumps, refrigeration equipment

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GAS DETECTION & MEASUREMENT
  Use of a Drager pump
  GAUGE, REFRIGERATION PRESSURE TEST
  How Colorimetric gas detection tubes work
  Using the TIF 5000 Gas Detector
  Warnings re instruments for detection of gases
  Warning: choose the right tube for gas detection
REFRIGERANTS
  GAUGE, REFRIGERATION PRESSURE TEST
  REFRIGERANT CHARGING PROCEDURE
  REFRIGERANT DRIERS & FILTERS
  REFRIGERANT LEAK DETECTION
  REFRIGERANT LEAK REPAIR
  REFRIGERANT METERING DEVICES TEVs
  REFRIGERANT METERING CAPILLARY TUBES
  REFRIGERANT PIPING & DISTANCES
  REFRIGERANT PRESSURE READINGS

TIF Instruments, Inc., 9101 NW 7th Avenue, Miami, Florida 33150 (This is where we've sent our TIF 8800 and TIF 5000 for repairs).
Jennifer Moore, Sales Administrator, Nextteq, LLC, Tampa FL, www.nextteq.com 813-249-5888. Nextteq is the master Distributor for Gastec in the United States. According to the company's website, Gastec Gas Sampling Pumps are the industry’s first and only pumps to provide on-the-spot measurement of ambient temperature. [Private email, JM to DF 5/23/08]
Air Conditioning, Heating, & Refrigeration Institute, [industry association], Air-Conditioning, Heating, and Refrigeration Institute (AHRI) 2111 Wilson Blvd, Suite 500 Arlington, VA 22201 USA, Tel: 703-524-8800, Email: ahri@ahrinet.org,
[1] Robinair® Robinair Manufacturing Corporation, Robinair Way, Montpelier OH 43543-9990 or more currently: OTC/SPX 655 Eisenhower Drive Owatonna, MN 55060 USA Phone (507) 455-7000 Fax (507) 455-8354. Customer service Tel: 800-628-6496. Technical support: 800-822-5561. Robinair provides a wide range of refrigerant charging equipment including gauges, hoses, automatic charging scales, and refrigerant recovery/recycling equipment.
[2] Robinair® Dial-a-charge charging cylinder description and instructions, Kent-Moore Robinair Manufacturing Corporation, Robinair Way, Montpelier OH 43543-9990 or more currently: OTC/SPX 655 Eisenhower Drive Owatonna, MN 55060 USA Phone (507) 455-7000 Fax (507) 455-8354. Customer service Tel: 800-628-6496. Technical support: 800-822-5561. Robinair provides a wide range of refrigerant charging equipment including gauges, hoses, automatic charging scales, and refrigerant recovery/recycling equipment.
[3] "Instructions for Kwik-Charge" ™ provided by Imperial Clevite, Inc., Fluid Components Division, 6300 West Howard St., Chicago IL 60468 (July 1982 device instructions)

How to diagnose and fix an air conditioning system that is not working

Since the failure of an air conditioner to turn on, loss of air conditioner cooling capacity, reduced air conditioning output temperatures, loss of cool air supply, or even loss of air flow entirely can be due to a variety of problems with one or more components of an air conditioner or air conditioning system, after reviewing the lost air conditioner cooling diagnosis procedures described in this article, be sure to also review the diagnostic procedures at each of the individual air conditioning diagnosis and repair major topics listed just below. To return to our air conditioning and refrigeration home page go to AIR CONDITIONING & HEAT PUMP SYSTEMS.

If your air conditioning or heat pump system has lost its cooling capacity or won't start select one or more of the diagnostic articles listed below.

A/C - HEAT PUMP CONTROLS & SWITCHES: air conditioner controls and switches - begin here if your A/C won't start. Here's an important tip: most refrigeration problems, in air conditioners, refrigerators, or freezers, are electrical, not mechanical. In air conditioning school, we used to drive out and collect abandoned refrigerators that people were tossing out during our community's spring cleanup week. Taking these appliances back into the shop we found that almost always the problem that had caused the owner to dispose of their air conditioner or freezer was in an electrical connection or electrical control. So it's worth checking out switches and controls on an air conditioner before replacing more costly components.
OPERATING DEFECTS: major air conditioning problem symptoms and how to get the air conditioning system working again,e.g. compressor or fan noises, failure to start, and inadequate cool air volume
LOST COOLING CAPACITY: what to do when not enough cool air comes out of the system
- What to check first if there is no cool air or not enough cool air
- Compressor failure diagnosis: basic checks of the air conditioner compressor
- Ducts & Air Handler diagnosis: basic checks of the indoor air handler (blower), air ducts, and filter systems
COMPRESSOR CONDENSER: problems with air conditioner compressor/condenser units
AIR HANDLER UNIT: problems with the air handler, air filters, and the cooling coil itself
DUCT SYSTEM DEFECTS: problems with the air duct system, air filters, supply registers, return air registers
A/C REFRIGERANT LEAK DETECTION: how to use a TIF5000 to detect air conditioning refrigerant gas leak
REFRIGERANT LEAK REPAIR - how to repair refrigerant leaks in piping, evaporator coils, condenser coils
A/C DIAGNOSTIC FAQs: air conditioning system diagnostic FAQs: Q&A about air conditioner repair - a detailed air conditioning system diagnostic checklist

Books & Articles on Building & Environmental Inspection, Testing, Diagnosis, & Repair

Our recommended books about building & mechanical systems design, inspection, problem diagnosis, and repair, and about indoor environment and IAQ testing, diagnosis, and cleanup are at the InspectAPedia Bookstore. Also see our Book Reviews - InspectAPedia.
GAS EXPOSURE EFFECTS, TOXIC Toxic Gas Exposure effects, including links to toxic gas exposure screening and gas testing protocols.
Gases: Toxic gases, indoor exposure levels, testing, identification

A Toxic Gas Testing Plan: A Gas Sampling Plan for Residential and Commercial buildings lists some of the toxic indoor gases for which we test, depending on the building complaint and building conditions
Gas Exposure Hazard Levels: for Toxic Gas Exposure to Ammonia, Arsine, Arsenic, Bromine, Carbon Dioxide, Carbon Monoxide, Hydride, Ozone - allowable exposure levels and hazard levels
Carbon Dioxide Gas Toxicity hazard level, poisoning symptoms, & testing
Carbon Monoxide Gas Toxicity hazard levels, poisoning symptoms, & testing
Formaldehyde: US EPA. UFFI (Urea Formaldehyde Foam Insulation) was previously considered a hazard (formaldehyde outgassing). Subsequent research virtually closed concern regarding this material; however formaldehyde appears to remain a health concern for sensitive individuals.
Ozone Warnings - Use of Ozone as a "mold" remedy is ineffective and may be dangerous.
Sampling for gases in air such as VOC's, MVOC's, toxic chemicals, and combustion products.
Unfortunately no single test or tool can detect all possible building contaminants. We use methods and equipment which can test for common contaminants. If the identity of a specific contaminant is known in advance we can also test for a very large number of specific contaminant gases in buildings.
We use gas sampling equipment provided by the two most reliable companies in the world, Draeger-Safety's detector-tubes and Drager accuro bellows pump, the Gastec cylinder pump and detector-tube system produced by Gastec. We also have used gas detection tubes by Gastec previously marketed for use with Sensidyne pumps but Sensidyne pumps now use Kitagawa gas detection tubes. We also use Sensidyne's Gilian air pump. For broad screening for combustibles and a number of other toxic gases and for leak tracing we also use Amprobe's Tif8850 and 8800, and the TIF 5000 automatic halogen leak detector (for air conditioning and cooling system refrigerant leak detection). All of these instruments, their applications, and sensitivities (minimum detectable limits) for specific gases are described in our Gas Sampling Plan online document.
Radon Gas U.S. EPA Radon level maps


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