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 Air Conditioning, Heat Pump & Refrigeration System Pressure Controls & Safety Switches
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InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.
This article explains where to find and how identify and adjust the refrigerant pressure operating and safety pressure controls for air conditioning and heat pump systems and similar equipment. These same controls are used on other refrigeration systems such as commercial coolers and freezers.
Green links show where you are. © Copyright 2013 InspectAPedia.com, All Rights Reserved. Author Daniel Friedman.
Air Conditioner or Heat Pump Operating Pressure Control Switch & Electrical Sensor Safety Switches
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 See A/C - HEAT PUMP CONTROLS & SWITCHES for our complete list of HVAC controls and switches. We include photographs to assist readers in
recognizing cooling system defects. Other articles at this website discuss certain of these controls in greater detail. See SYSTEM OPERATION for a discussion of thermostats, zone dampers, and circuit breakers on air conditioners and heat pumps. Also see THERMOSTATS and THERMOSTATIC EXPANSION VALVES.
If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS. See How to determine the cooling capacity of air conditioning equipment if the system seems to be working but is inadequate to cool your building. CONTACT us to add HVAC system switches or controls or diagnostic suggestions you do not find here.
We distinguish between operating control pressure switches and safety switches that monitor against too-low or too-high refrigerant pressures in a refrigeration system. Both are described here.
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Operating Pressure Control Switches for Air Conditioners, Heat Pumps, Refrigeration Equipment
Operating pressure control switches set the normal compressor cut-in and cut out pressures in commercial refrigeration systems including air conditioners, coolers, refrigerators freezers.
Commercial refrigeration equipment such as refrigerators (coolers) and freezers use a pressure control switch to set the cut-in and cut out pressures at which the compressor shall operate.
The pressure control switch and the thermostatic expansion valve may both need to be inspected, tested, and set to cooperate with one another, as I describe in an old field service call report described at REFRIGERANT METERING DEVICES TEVs
Shown at left is a Ranco™ single pressure control switch with an operating range of 12-50 psig and a differential range of 5-35 psig. Ranco produces a wide range of switches and controls including air conditioning controllers. This particular Ranco switch shown at left "opens" on low. Available from Grainger and other refrigeration equipment suppliers.
Among these refrigeration system pressure controllers, the Ranco Type "O" single function pressure controls are most common. These pressure control switches actually are designed to operate either as normal operating controls or as protection devices (see Safety Switches below). On these controls a "multi-capsule" pressure element operates a single or double pole electrical switch that typically will turn the compressor motor on or off.
Watch out: some pressure controls use a manual reset on their cut-out pressure feature. That means that your equipment may be shut down until you locate and press the reset bar on the equipment. Typically the reset bar is located on the top of the pressure control switch.
Pressure control switch sensor tubing warnings
Also for proper installation of one of these switches you should avoid sharp bends or kinks in the capillary tube sensor tubing, and don't let the tubing be exposed to vibration due to improper mounting or installation. Tubing that is too loose and vibrates can rub and wear through; tubing that is too tight can vibrate in what Ranco calls "violin string" vibration that can cause the tubing to break. And of course all refrigerant lines in the system will need to be purged when installing a new control.
Adjusting the refrigerant pressure control switch
You should not mess with the switch adjustment unless you are a qualified HVAC service technician since doing so risks damaging the equipment or causing an unsafe condition.
But FYI, in general, turning the RANGE adjustment screw inwards or "clockwise" (the right hand screw on the control top) will decrease the control pressure setting, and turning the screw out or counterclockwise will increase the pressure setting.
The DIFFERENTIAL setting screw (the left hand screw of the pair as you face the front of the control) turns in or clockwise to increase the differential and out or counterclockwise to decrease the pressure differential.
Note: you won't normally see this type of refrigeration pressure control switch on residential air conditioners, heat pumps, nor residential appliances.
Similar pressure control switches are used in many mechanical system operations including steam heat - see Pressure Switch, Steam Boiler and even on water pumps - see WATER PUMP PRESSURE CONTROL
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Refrigeration System Pressure Safety Switches: protect against over pressure or under pressure in air conditioning or heat pumps
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Some HVAC systems (air conditioners, heat pumps, refrigeration equipment) include other sensor switches that may include an electrical pressure or temperature transducer/sensor (photo at left) or an air conditioning or heat pump pressure sensing switch that detects improper (too high) or [in some systems including automotive air conditioning] too-low refrigerant pressures in the system.
 For safety the air conditioning or heat pump pressure switch can shut off the system. When pressures return to normal the pressure safety switch normally auto-resets and operation can continue.
Ranco also produces air conditioning safety controls: their G60 pressure controller (small photo at immediate left) is a cut-out switch that protects the refrigeration system compressor against abnormally low suction pressures that could otherwise cause liquid refrigerant to enter (and destroy) the compressor.
The Ranco G63 pressure controller is a high pressure cut-out switch that protects the refrigeration system against excessive compressor outlet or discharge pressure.
These air conditioner safety switches are offered in a range of models, depending on the cut-out and cut-in pressures desired. Cut out/in pressure ranges extend from 0.14 psi cut-out and 8 psi cut in up to 362 psi cut-out and <286 psi cut-in with variable differential settings.
Typically a low pressure safety switch to protect the compressor against liquid refrigerant will automatically reset when conditions return to normal. A high pressure safety switch may include an automatic reset and (for pressure decrease) a manual reset mode.
Watch out: As Ranco and others warn, both under pressure (that can damage the compressor) and overpressure (that can damage or eve blow something up) at an air conditioner or heat pump system - can be dangerous need to be guarded against.
Sources of pressure switches for refrigeration equipment include the
- Behr A/C pressure Switch (less than$30). and other automotive switches.
- Micro Pneumatic Logic pressure switches (wide range of applications).
- Ranco and Grainger - pressure control switches and pressure safety switches for air conditioning and refrigeration systems, protecting against overpressure and under pressure
- Sensata automotive air conditioning (A/C) pressure switches [dual function pressure switch provides high pressure cut-out (HPCO) with fan function or high side low pressure (HSLP) cutout functions
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Frequently Asked Questions (FAQs)
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Technical Reviewers & References
Related Topics, found near the top of this page suggest articles closely related to this one.
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- Thanks to AAlan Carson and Bob Dunlop, Carson Dunlop, Associates, Toronto, for permission to use illustrations from their publication, The Illustrated Home which illustrates construction details and building components. Carson Dunlop provides home inspection education, publications, report writing materials, and home inspection services. Alan Carson is a past president of ASHI, the American Society of Home Inspectors.
 Carson, Dunlop & Associates Ltd., 120 Carlton Street Suite 407, Toronto ON M5A 4K2. (416) 964-9415 1-800-268-7070 info@carsondunlop.com. The firm provides professional home inspection services & home inspection education & publications. Alan Carson is a past president of ASHI, the American Society of Home Inspectors. Thanks to Alan Carson and Bob Dunlop, for permission for InspectAPedia to use text excerpts from The Home Reference Book & illustrations from The Illustrated Home. Carson Dunlop Associates' provides:
- Commercial Building Inspection Courses - protocol ASTM Standard E 2018-08 for Property Condition Assessments
- Home Inspection Education Courses including home study & live classes at eleven colleges & universities.
- Home Inspection Education Home Study Courses - ASHI@Home Training 10-course program.
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on these courses: Enter INSPECTAHITP in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference Book, a reference & inspection report product for building owners & inspectors.
Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
- The Home Reference eBook, an electronic version for PCs, the iPad, iPhone, & Android smart phones.
Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter inspectaehrb in the order payment page "Promo/Redemption" space.
- The Illustrated Home illustrates construction details and building components, a reference for owners & inspectors.
Special Offer: For a 5% discount on any number of copies of the Illustrated Home purchased as a single order Enter INSPECTAILL in the order payment page "Promo/Redemption" space.
- The Horizon Software System manages business operations,scheduling, & inspection report writing using Carson Dunlop's knowledge base & color images. The Horizon system runs on always-available cloud-based software for office computers, laptops, tablets, iPad, Android, & other smartphones.
- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
- Thanks to Lester Richer, a professional home inspector, for the reminder that a bad air conditioner condensate drip tray switch can shut the whole system down.
- Behr Hella Service A/C pressure switches,
- Grainger, http://www.grainger.com/
- Ranco Corporation, http://www.invensyscontrolseurope.com/ranco/ Tel (Europe)
+44 (0)845 130 5522
- Sensata Technologies, 529 Pleasant Street, B41
Attleboro, MA 02703-2964
Phone: 1-248-692-5600
Fax: 1-248-692-5630
Email: auto-mktg@sensata.com
Web: www.sensata.com, pressure switches for automotive air conditioning systems
- Micro Pneumatic Logic, Inc., Pompano Beach, Florida Tel. (954) 973-6166 - pressure switches
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.
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
- 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
- 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
 The Home Reference Book - the Encyclopedia of Homes, Carson Dunlop & Associates, Toronto, Ontario, 25th Ed., 2012, is a bound volume of more than 450 illustrated pages that assist home inspectors and home owners in the inspection and detection of problems on buildings. The text is intended as a reference guide to help building owners operate and maintain their home effectively. Field inspection worksheets are included at the back of the volume. Special Offer: For a 10% discount on any number of copies of the Home Reference Book purchased as a single order. Enter INSPECTAHRB in the order payment page "Promo/Redemption" space. InspectAPedia.com editor Daniel Friedman is a contributing author.
Or choose the The Home Reference eBook for PCs, Macs, Kindle, iPad, iPhone, or Android Smart Phones. Special Offer: For a 5% discount on any number of copies of the Home Reference eBook purchased as a single order. Enter INSPECTAEHRB in the order payment page "Promo/Redemption" space.
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- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
- Modern Refrigeration and Air Conditioning, A. D. Althouse, C.H. Turnquist, A. Bracciano, Goodheart-Willcox Co., 1982
- Principles of Refrigeration, R. Warren Marsh, C. Thomas Olivo, Delmar Publishers, 1979
- "Air Conditioning & Refrigeration I & II", BOCES Education, Warren Hilliard (instructor), Poughkeepsie, New York, May - July 1982, [classroom notes from air conditioning and refrigeration maintenance and repair course attended by the website author]
- Refrigeration and Air Conditioning Technology, 5th Ed., William C. Whitman, William M. Johnson, John Tomczyk, Cengage Learning, 2005, ISBN 1401837654, 9781401837655 1324 pages
- Carson Dunlop, Associates, Toronto, have provided us with (and we recommend) Carson Dunlop Weldon & Associates' Technical Reference Guide to manufacturer's model and serial number information for heating and cooling equipment
Special Offer: Carson Dunlop Associates offers InspectAPedia readers in the U.S.A. a 5% discount on any number of copies of the Technical Reference Guide purchased as a single order. Just enter INSPECTATRG in the order payment page "Promo/Redemption" space.
 Air Conditioning SEER - New DOE Air Conditioner and Heat Pump Efficiency Standard- Asbestos HVAC Ducts and Flues field identification photos and guide
- Fiberglass: Indoor Air Quality Investigations: Fiberglass in Indoor Air, HVAC ducts, and Building Insulation
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