Commercial refrigeration equipment pressure control, RancoAir Conditioning, Heat Pump & Refrigeration System Pressure Controls & Safety Switches

  • PRESSURE CONTROLS & SAFETY SWITCHES - CONTENTS: Description of refrigeration pressure control switches - cut-in/cut-out controls for the compressor unit. Description of refrigeration system safety control switches that protect against over pressure or under-pressure on air conditioners, heat pumps, etc. Key switches and controls to check if your air conditioner or heat pump is not working
  • POST a QUESTION or READ FAQs about cooling system & heat pump system switches & controls
InspectAPedia tolerates no conflicts of interest. We have no relationship with advertisers, products, or services discussed at this website.

Air conditioning & heat pump pressure controls and switches:

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 2017, All Rights Reserved.

Air Conditioner or Heat Pump Operating Pressure Control Switch & Electrical Sensor Safety Switches

Electric sensor switch on commercial air conditioner (C) D Friedman Tomkiel

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.

[Click to enlarge any image]

If your air conditioning or heat pump system has lost its cooling capacity or won't start see REPAIR GUIDE for AIR CONDITIONERS.

See COOLING CAPACITY, RATED of air conditioning equipment if the system seems to be working but is inadequate to cool your building.

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 & EEVs


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.

Commercial refrigeration equipment pressure control, RancoAmong 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 CONTROL, STEAM BOILERS and even on water pumps - see WATER PUMP PRESSURE CONTROL

Refrigeration System Pressure Safety Switches: protect against over pressure or under pressure in air conditioning or heat pumps

Electric sensor switch on commercial air conditioner (C) D Friedman Tomkiel

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.

Ranco pressure safety switch

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.

Where to buy pressure control switches for refrigeration equipment

CONTACT us to add HVAC system switches or controls or diagnostic suggestions you do not find here.


Continue reading at REFRIGERANT METERING DEVICES TEVs & EEVs or select a topic from closely-related articles below, or see our complete INDEX to RELATED ARTICLES below.

Or 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.


Or see OPERATING CONTROLS, A/C & HEAT PUMP for a discussion of thermostats, zone dampers, and circuit breakers on air conditioners and heat pumps.


Or see these

Air Conditioning & Heat Pump Refrigerant Articles

Suggested citation for this web page

PRESSURE CONTROLS & SAFETY SWITCHES at - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.


Or use the SEARCH BOX found below to Ask a Question or Search InspectApedia


Frequently Asked Questions (FAQs)

Click to Show or Hide FAQs

Ask a Question or Search InspectApedia

Use the "Click to Show or Hide FAQs" link just above to see recently-posted questions, comments, replies, try the search box just below, or if you prefer, post a question or comment in the Comments box below and we will respond promptly.

Search the InspectApedia website

Comment Box is loading comments...

Technical Reviewers & References

Click to Show or Hide Citations & References

Publisher's Google+ Page by Daniel Friedman