Question? Just ask us!
Free Encyclopedia of Building & Environmental Inspection, Testing, Diagnosis, Repair
InspectAPedia ® Home
AIR CONDITIONING & HEAT PUMP SYSTEMS
A/C - HEAT PUMP CONTROLS & SWITCHES
AIR CONDITIONER COMPONENT PARTS
AIR CONDITIONER TYPES, ENERGY SOURCES
AIR FILTER EFFICIENCY
AIR FILTERS, FIBERGLASS PARTICLES
AIR FLOW MEASUREMENT CFM
APPLIANCE DIAGNOSIS & REPAIR
APPLIANCE EFFICIENCY RATINGS
BLOWER DOORS & AIR INFILTRATION
BLOWER FAN CONTINUOUS OPERATION
BLOWER FAN OPERATION & TESTING
BOOKSTORE - Air Conditioning "How To" Books
CAPACITORS for HARD STARTING MOTORS
CLEANING & Legionella BACTERIA
CHINESE DRYWALL HAZARDS
CONDENSATION or SWEATING PIPES, TANKS
DEFINITION of HEATING & COOLING TERMS
DEW POINT CALCULATION for WALLS
DEW POINT TABLE - CONDENSATION POINT GUIDE
DIAGNOSTIC GUIDES A/C / HEAT PUMP
DIAGNOSE & FIX HEATING PROBLEMS-BOILER
DIAGNOSE & FIX HEATING PROBLEMS-FURNACE
DUCTS - Asbestos
DUCT INSULATION, Asbestos Paper
DUCT INSULATION for SOUNDPROOFING
DUCT SYSTEM & DUCT DEFECTS
DUCT SYSTEM NOISES
DUCTS, Asbestos Transite Pipe
DUST, HVAC CONTAMINATION STUDY
ELECTRIC MOTOR OVERLOAD RESET SWITCH
EVAPORATIVE COOLING SYSTEMS
FAN LIMIT SWITCH
GAS EXPOSURE EFFECTS, TOXIC
GAS DETECTION INSTRUMENTS
HEAT LOSS (or GAIN) in buildings
HEAT LOSS (or GAIN) INDICATORS
HEAT LOSS R U & K VALUE CALCULATION
HEATING SMALL LOADS
INSPECTION CHECKLIST - OUTDOOR UNIT
INSPECTION LIMITATIONS, A/C SYSTEMS
LEED GREEN BUILDING CERTIFICATION
LOST COOLING CAPACITY
LOW VOLTAGE TRANSFORMER TEST
MOTOR OVERLOAD RESET SWITCH
MOLD in AIR HANDLERS & DUCT WORK
OPERATING COST, AIR CONDITIONER
OPERATING DEFECTS, AIR CONDITIONING
REPAIR GUIDES A/C / HEAT PUMP
REPAIR & DIAGNOSTIC FAQs for A/C
THERMOSTATS, HEATING / COOLING
THERMOSTATIC EXPANSION VALVES
WATER COOLED AIR CONDITIONERS
WINDOW / WALL AIR CONDITIONERS
WINDOW / WALL A/C SUPPORTS
Air conditioner & heat pump refrigerant test gauges: this article describes the connections, use, and reading of a refrigerant gas pressure test gauge set. We describe the procedure for using test gauges when adding or replacing refrigerant: charging an air conditioner, heat pump, refrigerator with refrigerant gas.
We explain how a refrigeration gauge set should be connected to HVAC equipment to avoid contamination damage and we review the refrigeration system evacuation and cleaning procedure.
Green links show where you are. © Copyright 2014 InspectApedia.com, All Rights Reserved.
Details on Proper Use of the Refrigeration Charging / Testing Gauge Set to Keep Moisture & Dirt out of an Air Conditioner, Heat Pump, Refrigerator, Freezer, etc.
To keep moisture out of a refrigeration system, in addition to finding and fixing leaks, we need to know how to properly use a refrigerant gauge set with charging lines, and how to use cap off plugs on the charging fittings.
To be clear, when connecting an HVAC refrigeration gauge set to test fittings on an air conditioner or heat pump we must:
Refrigeration Servicing Gauge Set Installation & Use
Reading the Gauges on a Refrigeration Gauge Set
We use (and illustrate) a traditional Imperial System Analyzer gauge set that provides three charging lines (refrigerant canister, high side, low side). This is a diaphragm type gauge but other methods of measuring and charging systems are available.
How to Read the Low Pressure Side Refrigerant Gauge
The compound gauge at left is used on the low pressure side of the system and shows pressure readings in black, from 0 to 300 psi gauge pressure. [Click any image to see an enlarged, detailed version.]
Temperature corresponding to pressure is shown in red on this gauge for R12 and R22, or for newer refrigerants on newer gauges.
Vacuum is also shown on this gauge on a scale from 0-30 in. Hg. in green..
Reminder: as we discuss at REFRIGERANT PRESSURE READINGS if you use pressure test gauges (GAUGE, REFRIGERATION PRESSURE TEST) to measure the refrigerant pressure in the static or equalized air conditioning or heat pump system, the gauges only tell you the refrigerant pressure, not the quantity of refrigerant that is present in the system.
For example at 70F ambient temperature and with R12 refrigerant, the static system pressure would be at 70 psi as long as there is enough refrigerant in the system to have at least some in liquid state.
Reading the High Pressure Side Refrigerant / HVAC Test Gauge
The compound gauge on the right of this gauge set is used on the high pressure side of the refrigeration system and shows refrigerant pressures, typically from 0 - 500 psi on the black scale or 0 - 35 KG/CM3 on the outermost red scale.
In the center of the refrigerant gauge the red scales give temperature readings for three older refrigerants (this is an old gauge): R502, R12, and R22.
Attaching the Refrigeration Gauge Set to the Air Conditioner, Heat Pump, or other refrigeration equipment
Find the service ports
Central air conditioning systems, heat pumps, and split systems typically have service ports installed specifically for the attachment of test gauges for system inspection, evacuation, and charging.
Residential refrigerators, freezers, and window or portable air conditioners typically will not have these service ports. To service one of those latter devices you'll need to cut the refrigerant line and install (solder in place) a tee and a service port.
Our photo (left) shows four covered service ports on this split system compressor/condenser unit. That's because this unit supports two indoor wall-mounted cooling units.
If its not obvious to you that the larger diameter line is the low pressure or suction side and the smaller diameter refrigerant line is the high pressure side, then really you should not be messing with this equipment before taking a refresher class in HVAC servicing and repair.
Using Temporary Access Valves for HVAC or Refrigeration Testing & Diagnosis
Tapaline® and other piercing valves are available in various sizes to allow the HVAC technician to tap into the refrigerant lines on a system in order to perform diagnosis where there are not already service valves installed. Smaller bullet-type valves are installed using an allen wrench.
Use these valves as a temporary service tool, preferably attached on the process tube. [See Types of air conditioner or heat pump compressors & compressor designs if you don't know what a process tube is.]
Watch out: do not leave these temporary test valves on the refrigerant piping - you're asking for a future leak. These valves are suitable to aid diagnosis of a refrigeration system by avoiding disturbing the troubled state of the system (as you'd do if you had to cut lines and solder in service valves just to do a test).
After using a temporary tap-in valve on the process tube at a compressor unit, you should solder off the line puncture and add a permanent service valve fitting - the type that uses a schrader valve and cap - also referred to as an access valve or line valve.
Connect the Test Gauges to the Air Conditioner, Heat Pump, etc
In the shop we connect both high and low pressure gauges to the equipment being tested. In the field technicians often use only the low pressure side of the HVAC test gauge set, since high side problems also show up on the low side.
On test gauge sets such as ours shown here, the service lines always open or close a connection between the HVAC equipment refrigeration test ports and the gauges. The end-valves (silver handles) on either side of the gauge set then open or close a further connection between that valve and either high or low side connection and the yellow hose that will in turn connect to a refrigerant source.
You'll notice in our photo that both ends of the refrigerant hoses are attached to the gauge set. On the front of this gauge (and more easily seen in the photograph) are three blind connector plugs to which we connect the hoses when the gauge is not in use - this step is to help keep the gauge hoses clean of debris.
In the photo at left, the "live" hose connection ports are somewhat hidden behind the gang of hoses and the "blind" connectors used to keep the hoses and their end connectors clean when not in use.
The gauge set has stop valve handles that you see on either side of the gauge. These controls open or close the high or low side service lines once they have been properly connected to the high or low side service port.
As we've mentioned before, we would not normally connect our gauge set to the service ports without first attaching a can of the proper refrigerant to the gauge set service port and then using that refrigerant to purge any air that may be in the refrigerant hoses. That's to avoid blowing air and contaminants into the HVAC system.
On our air conditioner or heat pump test gauges we use a
Depending on which valves you open or close, this gauge set permits charging the refrigerant system on either the high side or the low side.
Refrigerant Test Gauge Hose Hookup Details
Watch out: not all HVAC test gauge sets may have their high pressure and low pressure gauges in the same left and right positions.
What is critical is that the low pressure gauge is connected to the low pressure port (by convention using a blue hose) and the high pressure gauge is connected to the high pressure port (by convention using a red hose).
Watch out: Valves (D) and (E) are used to isolate their sides from the service port.
Open only one control valve at a time, then close it before opening the other.
Watch out: as we warn at many places in this article series, do not send liquid refrigerant into the low side of a refrigeration system. Liquid refrigerant will enter the bottom of the compressor motor and can damage the compressor, or even if the compressor tolerates and passes the refrigerant through its pumping system, the refrigerant can carry away the lubricating oil from the compressor, and/or cause an air trap in the system.
We use the same procedure for attaching the gauges to the high side of the system.
Restating a bit:
For the gauge set shown above, turn the valves all the way out to attach the gauges, since service ports are stopped OFF.
To Remove the Service Test Gauges on Refrigeration Equipment
Back-seat (all the way out) the equipment service valve to close off the service port, then remove the gauge and cap both the service port and the test gauge hose ends.
Green link shows where you are in this article series.
Frequently Asked Questions (FAQs) About Refrigeration & Air Conditioning or Heat Pump Refrigerant Gas Pressure Test Gauge Use
No FAQs have been posted for this page. Try the search box below or CONTACT US by email if you cannot find the answer you need at InspectApedia.
Question: what is a good R14 refrigeration pressure ? What should the refrigerant pressure be in my unit?
model cxa6 keeprite unit r14 refrigeration what psi pressure it should be good. - Litt 7/26/2011
what are the low and high readings for a 7.5 ton, 220 three phase compressor with two cooling coils and serves two inside units, mod BTA090C300H0, SER W01 195521 - firstname.lastname@example.org 8/2/11
I add that for R14, its Latent heat of vaporization (1.013 bar at boiling point) is 135.7 kJ/kg
You need to consul the manufacturer's technical literature for the refrigerant gas in use and the compressor model in use, and then you'll need to use a table of gases that provides temperature and pressure data in one place, as ambient temperature affects the answer. In sum there is no single precise right number. There are typical operating ranges of refrigerant pressures, as you can see a REFRIGERANT PRESSURE READINGS. Also take a look at our answer to Mr. Litt, just above.
Question: what causes excessive refrigerant pressure?
what cause to much high pressure - Anonymouse
Anon: among the reasons for excessively high pressure on the HIGH Side or output side of the compressor/condenser section of an air conditioner or heat pump are a plugged or debris blocked condensing coil, plugged refrigerant line, plugged dryer/filter on the line, or a stuck refrigerant metering device such as a capillary tube or thermostatic expansion valve. There may be other causes of high refrigerant pressure that other readers can add.
Question: High pressure readings on the low side of my heat pump
I am getting very high pressure readings on the low side of my heat pump. The discharge and return line to the air handler are cool and equal in temp.(showing no refrigerant movement), But my suction line and discharge line leading in to and out of my compressor are very hot. Have open the lines and checked the orifices and they are clear as is the lines to the air handler. Is it possible that the condensing alone can be clogged? I did have a compressor burn out last year. - D. Nix 8/7/11
High pressure on the low side sounds to me as if a metering device is stuck wide open; perhaps when your compressor burned up last year it left some debris in the refrigerant lines that has found its way to the TEV and has jammed it. Ask your HVAC tech to check the system again, check the TEV adjustment, and also consider installing a (new) filter/drier on both ends of the refrigerant piping system.
Question: can a refrigerant gas leak be fixed or does the whole compressor need replacement?
I need to know whether a leak form one of the compressor tubes is fixable or not. My technician said that the whole compressor would need to be replaced. - Ehab 8/176/11
Ehab refrigerant leaks can be repaired by various patch methods. But if the leak is discovered to be a symptom of more extensive corrosion, such as at a cooling coil, it's a much bigger repair than just a patch. I'm not sure why, if the compressor was working normally, you'd need to replace all the equipment- perhaps the tech is referring to the issue that s/he cannot any longer recharge with R12 or R22 - used in older compressors, but there are alternative refrigerants that can often work with some adjustments.
Question: Comment on hose color coding; How do I know if the HVAC Tech Put In Enough Refrigerant?
Blue line goes to bigger line in compressor and red on little line
Hello, For a typical home split air conditioner, how to make sure that the technician has filled in enough gas in the out door compressor unit? - Sanjay 7/21/2012
Sanjay, without evacuating the air conditioner completely and putting in a precisely measured charge using gauges and metering equipment, you cannot know yourself exactly how much refrigerant is in the system. But there are indications of the refrigerant charge being too much or too little that can show up without sophisticated instruments. For example:
- if you hear a bubbling sound in the liquid line the charge may be low
- if you see bubbles in the sight glass (usually only found on commercial refrigeration equipment and on some residential air conditioner or heat pump systems) the charge may be low
- if the cooling coil is frosting over one of the causes is low refrigerant charge
- if the compressor makes a horrible clanking sound and then stops dead, one of the possible causes is overcharging or another problem (such as a failed TEV or other refrigerant metering control) that has caused liquid slugging of the compressor on the suction side.
Beyond these observations, you need to be able to trust your HVAC technician. While mistakes are of course possible, no service tech any credible motive for placing an improper refrigerant charge into the system. Doing so just makes more work and trouble for everyone.
Try the search box just below or if you prefer, post a question or a comment in the Comments box below and we will respond promptly.
Search the InspectApedia website
HTML Comment Box is loading comments...
Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
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.