Here's a common scenario. You go on a service call, put your gauges on a condensing unit, and find that the suction pressure is low. What do you do? In too many cases, the answer is "add refrigerant." But doesn't it seem like a good idea to confirm that low refrigerant is the problem before you start adding refrigerant? That's why checking superheat and subcooling is so important. Let's go back to the beginning. You go on a service call and find low suction pressure. However, this time you consider the three main causes of low suction pressure, and check superheat and subcooling to make the correct diagnosis. CAUSE #1: Insufficient heat getting to evaporator. This can be caused by low air flow (dirty filter, slipping belt, undersized or restricted ductwork, dust and dirt buildup on blower wheel) or a dirty or plugged evaporator coil. Checking superheat will indicate if the low suction is caused by insufficient heat getting to the evaporator. To check superheat, attach a thermometer designed to take pipe temperature to the suction line.

Don't use an infrared thermometer for this task. Then take the suction pressure and convert it to temperature on a temperature/pressure chart. Subtract the two numbers to get superheat. For example, 68 psi suction pressure on a R-22 system converts to 40F. Let's say the suction line temperature is 50F. Subtracting the two numbers gives us 10F of superheat. Superheat for most systems should be approximately 10F measured at the evaporator; 20F to 25F near the compressor. If the suction pressure is 45 psi, (which converts to 22F) and the suction temp is 32F, the system still has 10F of superheat. The fact that these readings are normal indicates the low suction pressure is not caused by low refrigerant, but insufficient heat getting to the evaporator. CAUSE #2: Defective, plugged, or undersized metering device. Let's say a system has 45 psi suction pressure (converts to 22F) and 68F suction line temperature, the superheat is 46F (68 minus 22). This indicates low refrigerant in the evaporator.

However, before adding refrigerant, check the subcooling to be sure the problem isn't caused by a defective, plugged, or undersized metering device. While superheat indicates how much refrigerant is in the evaporator (high superheat indicates not enough, low superheat indicates too much), subcooling gives an indication of how much refrigerant is in the condenser. Subcooling on systems that use a thermostatic expansion valve (TXV) should be approximately 10F to 18F. Higher subcooling indicates excess refrigerant backing up in the condenser. On TXV systems with high superheat, be sure to check the subcooling as refrigerant is added. If the superheat doesn't change, and the subcooling increases, the problem is with the metering device. In the case of a TXV, it's likely that the powerhead needs to be replaced. To check subcooling, attach a thermometer to the liquid line near the condenser. Take the head pressure and convert it to temperature on a temperature/pressure chart. Subtract the two numbers to get the subcooling.

For example, 275 psi head pressure on an R-22 system converts to 124F. The liquid line temperature is 88F. Subtracting the two numbers gives 36F. High superheat and high subcooling indicates a problem with the metering device. Keep in mind that subcooling won't increase on systems with a liquid line receiver, as extra liquid will fill the receiver instead of backing up in the condenser. Receivers are rare on air conditioning systems, but very common on small refrigeration systems such as walk-in coolers and freezers. carrier ac parts arizonaIf a system with a receiver has high superheat and the liquid line sight glass is full of liquid (no bubbles), check the metering device. air conditioner units for rentIf the sight glass has bubbles, the system could be low on refrigerant, or the liquid line filter/dryer could be plugged. where to buy ac window units

Your clue here is that a noticeable temperature drop across a liquid line filter/dryer indicates it's plugged. There are indeed some cases where low suction pressure is going to be caused by low refrigerant. If the superheat is high and the subcooling is low, the refrigerant charge is probably low. Just keep in mind two things here: first, find and fix the leak. Second, monitor both superheat and subcooling as you add the refrigerant, to prevent overcharging. Skip Egner is a technician with CS Service Experts, Ft. Myers, FL. He has been in the HVAC industry for 30 years, and in 2006 won the North American Technician Excellence (NATE) Certified Technician Competition-at HVAC Comfortech. He can be reached at 239/768-2665. As a "Top Tech," here's what Egner says about NATE: "A service technician needs to have a high mechanical aptitude and the ability to understand complex mechanical systems. NATE certification is important to let the customer know that the technician working on their system has been trained and tested, and is competent to solve the problem."

LADWP is delivering two (2) light-emitting diode (LED) bulbs to all residential customers to help Save Energy LA. Switch from incandescent and compact fluorescent lamps (CFLs) to LEDs and save $238 in electric costs over the lifetime of each bulb. LEDs last longer and save money and electricity. Deliveries began in September and will continue through end of 2016. Be on the lookout for your LED bulbs, they will arrive in a great-looking, reusable bag – ideal for toting groceries or your work lunch – and a Save Energy LA brochure that lists our many programs and rebates for saving electricity. Let’s put our energy in to saving it! Residential customers can receive a $50 rebate, along with free pick-up, when they turn-in older refrigerators and freezers. The old appliance will be recycled in an environmentally responsible manner which meets the Environmental Protection Agency’s criteria. Eligible units must be fully operational and satisfy certain age and size requirements.

LADWP’s contractor, Appliance Recycling Centers of America (ARCA), will work with the customer in scheduling an appointment to pick up the old appliance. The Certified Pool Pump Replacement (CPPR) Program offers, for a limited time, up to a $1,000 rebate to LADWP residential customers who have in-ground swimming pools filtered with a single-speed pool pump.   LADWP offers the Consumer Rebate Program (CRP) to our residential customers to promote the use of energy-efficient products. This program is designed to both educate and encourage LADWP residential customers to purchase and install qualifying products in their home. Rebates are offered for various measures such as pool pump motors, high-efficiency windows, heating ventilation and air condition (HVAC) systems, refrigerator/freezer recycling, whole house fans, and others. This program offers incentives to both residential and non-residential customers who lease or purchase solar systems for installation on their property.

The current incentive level for the residential SIP is $0.40/watt and $.70/watt for the non-residential SIP. In addition, the programs allows for an higher incentive for non-profit agencies as well as educational institutions. The resulting incentive is calculated based upon the estimated annual production of the installed system.  For a limited time, the Efficient Product Marketplace (EPM) provides customers an opportunity to research, locate, and purchase energy efficient products from a single website. The EPM is a convenient, one-stop web based solution that provides a selection of popular energy efficient brands available at numerous stores and online retailers, pricing and available rebate information on eligible products, and quick rebate turnaround. All submissions are made electronically, with no paperwork to mail. Rebates are provided via a prepaid LADWP gift card that can be used anywhere where Visa credit cards are accepted. LADWP’s AC Optimization Program provides services by certified HVAC technicians to analyze your cooling systems and provide basic maintenance and efficiency services to keep your AC running optimally.

This service is free for all eligible residential and commercial LADWP customers with qualifying central AC units sized 1-10 tons. Services include system performance diagnostic tests, air filter replacement, and cleaning of the outside condenser coils. provides rebates to offset your out-of-pocket costs for the purchase of a qualifying electric vehicle (EV) charger to encourage the installation of a qualifying EV charger at residential and commercial locations. This program benefits the environment and helps EV drivers save fuel costs at the same time. The rebate is offered to residential customers who purchase or lease a qualifying EV and install a Level 2 charger at their home. It is also available to commercial customers who seek to install EV chargers for their employees and/or customers.  The Energy Upgrade California™ Program is a collaborative effort among California counties, cities, non-profit organizations, the state’s investor-owned utilities, and publicly owned utilities to deliver a California statewide “whole house” residential retrofit energy efficiency program, in which LADWP partners with Southern California Gas Company (SoCalGas®).

EUCA offers incentives to homeowners who complete selected energy-saving home improvements on single-family residences or 2-4 unit buildings, such as townhouses, condominiums, etc. The City Plants Program provides free shade trees for residents and property owners in Los Angeles to promote the planting of trees to improve building energy efficiency.  This is a joint program implemented by LA Department of Public Works and supported by LADWP. Through this partnership, CP is able to provide free shade trees for residents and property owners in the City of Los Angeles along with information on where to plant the trees for maximum energy efficiency benefits. CP currently focuses on providing trees for residential customers but will also provide trees to commercial customers. This program is a partnership with the Metropolitan Water District to offer numerous rebates for residential customers who purchase and install water conservation equipment. Rebates are offered for various measures such as rain barrels and cisterns, high-efficiency clothes washers, high-efficiency toilets, weather-based irrigation controllers and others.