Cool runnings

By Steve Schaeber, MACS Technical Editor

The main purpose of a thermostat is to help the cooling system regulate engine operating temperatures to within the manufacturer’s specification. This is normally done by first remaining closed to allow engine coolant to warm up, and then gradually open all the way as temperatures near spec. But sometimes this doesn’t happen, as in the case of a fully or partially stuck open thermostat.

When a thermostat sticks open, engine coolant is allowed to circulate without much restriction throughout the cooling system. This sounds great, and it’s important for this to happen after the proper operating temperature is reached.  However, if it happens too soon the engine coolant may not be able to reach a high enough temperature. This problem occurs because modern cooling systems are actually quite efficient, and are able to transfer a lot of heat from a lot of liquid in a relatively short period of time. When the coolant is not allowed to warm up fully, it basically circulates from the engine to the radiator and back to the engine, losing so much heat with each pass that it stays relatively cool.

Problems attributed to a cold running engine include lower HVAC heater output, engine performance issues and increased tailpipe emissions. But it also prevents the evaporation of condensation that forms on the inside of the engine block. If this water doesn’t burn off it can oxidize the metal (producing rust) and cause an oil sludge buildup in the bottom of the pan.

Engine oil is also affected by the thermostat, and it’s important for it to reach an operating temperature of approximately 190°F. Oil that is cold is not quite as viscous as the substance when it’s warm. Transmission oil coolers are also affected because they are generally in direct contact with engine coolant.

An easy way to determine if a thermostat may be stuck open is to simply monitor coolant temperature. Some vehicles have a dashboard temperature gauge, but many technicians prefer to use a scan tool with graphing capabilities. Begin when the engine is cold and connect your scan tool before starting the engine. Graphing the coolant temperature sensor PID will allow you to watch the thermostat to see what happens over time. If the thermostat is only partially stuck open, you may notice a rise in value to a relatively warm number, perhaps around 150°F. But if it’s stuck open all the way, temperatures may not increase much past 120°F.

Many PCMs will also monitor thermostat operation, illuminate the check engine light and produce a trouble code if there’s a problem. Ford uses P0125, Insufficient Coolant Temperature for Closed Loop Fuel Control, along with P0128 Coolant Thermostat (Temperature Below Thermostat Regulating Temperature). Issues could be related to slow warm up times, low coolant level, or sensor output issues, as well. Sensor readings may be double checked by using a mechanical thermometer or a thermocouple connected to a digital meter.

Posted in ACtion Magazine, MACS Member, Mobile Air Conditioning, Training | Tagged , , , , , , , , | Leave a comment

Thermocycle leaks

Radiator leaks are nothing new, and some technicians may initially blame a faulty part, poor construction or shoddy workmanship during installation when a leaker shows up in their bay, particularly when it’s a later model vehicle that has failed. But sometimes the radiator may be the victim of rapid coolant temperature changes caused by a faulty or rapidly degrading thermostat that is opening and closing too often.

When this happens, hot, then cold, then hot, then cold, then hot, then cold (you get the idea) coolant is sent from the engine block to the radiator, effectively shocking it back and forth from hot to cold and then back again, over and over. This rapid change is called thermocycling, and it causes radiator tubes to quickly expand and contract so much that they disconnect from the radiator’s side tanks, allowing coolant to leak out. It’s a failure similar to those found in the solder joints of copper pipes or on electronic circuit boards.

GM has identified similar issues in vehicles including certain 2014-2015 Chevrolet Silverado, Suburban, and Tahoe models, as well as the GMC Sierra, Yukon and Denali, and the Cadillac Escalade with 4.3, 5.3, or 6.2L engine. In a series of Technical Service Bulletins, which include #PI1513B titled, “Coolant Smell and/or Slight Leak at Radiator,” issued on November 30, 2016, GM presents comments made by customers, such as smelling coolant while driving or when outside the truck. These complaints may or may not include a coolant leak under the front of the vehicle.

GM recommends that technicians begin their diagnostics by inspecting the radiator for any signs of leaks, such as those that may exist where the flat radiator tubes meet the side header tanks. Particular attention should be paid to the four corners of the radiator, areas which may experience the most fluctuations. The cause could be related to excessive thermocycling of the cooling system,  brought on by excessive cycling of the thermostat.


Technicians’ initial conclusions are often an incorrectly constructed radiator , or a weak tube to header joint, which allows coolant to leak. In some cases, the technician may successfully replace the leaky radiator only to have the replacement fail after a period of time, ultimately causing the owner to bring the car back to the shop, The technician could assume the replacement radiator is also defective and  exchange it once more. But the actual root cause of the fault may be the thermostat, which if it cycles open and closed too often, can shock the radiator by sending out cool and hot coolant. Ideally the temperature of the cooling system should remain constant, or change slowly over time without rapid, frequent or excessively wide changes in temperature.

The final fix includes not only a thorough inspection and replacement of the radiator to solve the leak problem, but also changing out the thermostat, and of course, GM has an updated part number to address the overcycling.

Posted in MACS Member, Mobile Air Conditioning, Training, Uncategorized | Tagged , , , , , | Leave a comment

MACS mobile A/C diagnostics app is now available for download for MACS members

In response to MACS member needs and changing technology MACS has partnered with Shiftmobility to create the MACS mobile A/C diagnostics app for use on mobile devices. The app will include access to the MACS Service Reports and ACTION Magazine archives, checklists to aid system diagnosis, access to MACS member manufacturers and distributor suppliers and an extensive mobile A/C vehicle specifications library.

Vehicle reference specs will include:

A/C & Heater Service, A/C System Specifications, Component Location Diagrams – HVAC Systems Only, Cooling System Bleed, Diagnostic Trouble Codes – HVAC Systems Only, Miscellaneous Capacities – HVAC Systems Only, Radiator & Hose Replacement Procedures and Wiring Diagrams – HVAC Systems Only.

Only MACS members in good standing will have access to this APP. To access the MACS Mobile A/C Diagnostics app visit the Google play store for android devices or the iTunes store for Apple devices. One free download is included with MACS membership. Additional downloads are $60 each. For a larger overview and users guide click here.

After you choose the app, MACS will verify your membership and approve your use.

For more information email or call 215-631-7020 x 304.

Not a MACS member? Join here. 

Posted in #1234yf, Automotive, MACS Member, Mobile Air Conditioning, Training | Leave a comment

Today’s technicians need to be total climate control management forensic scientists  


MACS June ACTION Magazine is all about mobile A/C diagnostics!

By Peter Orlando, MACS Contributor

 Technicians need proper skills to work on today’s climate control systems. It is up to industry professionals to ensure they are service-ready and have all the necessary certifications and safety awareness training before they attempt any A/C service work on a vehicle.

We are required to perform a diagnostic system performance test to determine what diagnostic direction we will take on the problem based on the customer’s complaint. Many times, we need to determine up front if a problem is addressed by a Preliminary Inspection or TSB. If we don’t, we can waste many hours on a problem. Following proper OEM test procedures is essential for achieving a job well done, delivered on time and at the price agreed upon while making a profit. Read the rest of the story here.

Download the entire June 2017 MACS ACTION Magazine

Posted in #1234yf, ACtion Magazine, MACS Member, Mobile Air Conditioning, Refrigerants | Tagged , , , , , , , | Leave a comment

MACS Summer of Service Videos

Calling all MACS members! MACS is launching the summer of service videos!

Send us a short mobile A/C technical tip video less than 10 minutes that explains a service procedure or is educational and not overly commerical and we will post it on our website homepage for one week this summer.

You must send us an embed link and again not overly commercial it is fine to mention a product but we are looking for solid tech tips.

This is a great opportunity for MACS member companies to get more traffic for their service videos and help educate the industry.

Email your video embed link to

MACS reserves the right to refuse any video we deem not to be appropriate.

You must be a member of MACS to participate.

Posted in #1234yf, ACtion Magazine, Mobile Air Conditioning | Leave a comment

Honeywell opens new R-1234yf plant in Louisiana

Honeywell announced that it has started commercial operations at its new manufacturing plant in Geismar, La., to meet the growing global demand for its next-generation mobile air conditioning refrigerant. With this start-up, the plant has become the world’s largest site for producing HFO-1234yf, sold commercially as Solstice® yf.

Have you ever wondered what a refrigerant plant looks like? Here are some photos of their new operation courtesy of Honeywell.

Posted in #1234yf | Tagged , , , , | Leave a comment

Clinics, clinics and more mobile A/C clinics!

MACS has been busy training all around North America. Here are a few photos from the clinics…

MACS Mobile A/C Update Class in Bethlehem, PA with MACS Steve Schaeber

MACS heavy-duty mobile A/C class at Arctic Traveler with MACS Mike Bailey

MACS Mobile A/C Update Class in Waxahachie, TX at Tubes ‘n Hoses wit Jerry Lemon

Posted in Automotive training, MACS Member, MACS Training Event, Mobile Air Conditioning, Uncategorized | Tagged , , , , , , | Leave a comment

Do you have the right tools to repair mobile A/C systems?

Global Service Horizons


2017 MACS Worldwide Trade Show puts the future in plain sight

May I share something with you? Of all the automotive industry events I cover each year, it is the annual Mobile Air Conditioning Society Worldwide (MACS) Training Event and Trade Show that I most enjoy attending. Now let me tell you why.   Read the whole article

Download the May 2017 Issue


Posted in #1234yf, ACtion Magazine, MACS Member, Mobile Air Conditioning, Training | Tagged , , , , , | Leave a comment

What happened at the 2017 MACS Training Event?

The April 2017 issue of award-winning MACS ACTION magazine is now available with a comprehensive wrap-up of all the training classes presented at MACS 2017 Training Event and Trade Show. View what’s inside

Posted in #1234yf, ACtion Magazine, MACS Member, MACS Training Event, Mobile Air Conditioning, Refrigerants, Training | Leave a comment

Robinair and MACS Worldwide to provide free Section 609 test prep webinar and online test on May 9


Robinair and MACS Worldwide to provide free
Section 609 test prep webinar and online test on May 9

Robinair is partnering with the Mobile Air Conditioning Society (MACS) Worldwide to provide a free Section 609 test prep webinar for training and certification for up to 125 technicians on Tuesday, May 9 at 4 p.m. EDT. The webinar will be broadcast on a private YouTube channel. Registrants will receive the link to the webinar in advance of the webinar and a link for the test after the webinar.

The webinar will take approximately 90 minutes and at the end technicians can become Section 609 certified to work on vehicles using R-12, R-134a and R-1234yf refrigerant when they take the online test provided and successfully pass the test.

Interested technicians can register by calling 215-631-7020 x 0 or by registering online at under the EVENTS TAB.

When technicians register for the webinar, they will receive a link to the webinar in advance of the event free of charge and courtesy of Robinair. Technicians should take the online test immediately after viewing the webinar on May 9. If they pass the test, Section 609 credentials will be sent to them. Should a technician fail the test, one online re-test will be issued.

R-1234yf refrigerant is gaining popularity among vehicle manufacturers because it reduces the environmental impact of A/C systems in vehicles, helping manufacturers meet stringent vehicle emissions standards. Automakers can receive emissions credits for using environmentally friendly refrigerants, meaning aftermarket technicians will begin to see an increase in vehicles using R-1234yf.  The number of vehicles using

R-1234yf is expected to increase exponentially in the coming years as the refrigerant replaces the current industry-standard R134a.

The MACS refrigerant recovery and recycling program was developed to meet the requirements under Section 609 of the Clean Air Act and was formally approved by the U.S. Environmental Protection Agency (EPA), effective Aug. 13, 1992.  Since then, more than one million technicians have achieved Section 609 certification through its program. Throughout the years, MACS has continually expanded its certification program to reflect industry changes in technology, service equipment, procedures, tools, alternative refrigerants and changing government regulatory requirements.

“It’s a very natural fit for Robinair to partner with the MACS certification program to educate, train and certify today’s technicians on the latest breakthroughs and advancements in the mobile air conditioning industry,” said Tim Wagaman, senior product manager, air conditioning & fluid products, Robinair. “As R-1234yf becomes more prevalent in vehicles on the road, technicians and shop owners need training to recognize which refrigerant is being used, how to handle it safely and how to make sure they are properly equipped with the right machines and tools to service them.”

Since 1981, the Mobile Air Conditioning Society (MACS) Worldwide has been the advocate for service and repair owners, distributors, manufacturers and educators making their living in the total vehicle climate and thermal management industry.

MACS Worldwide empowers members to grow their businesses and delivers tangible member benefits through industry advocacy with government regulators and by providing accurate, unbiased training information, training products, training curriculum and money-saving affinity member services. MACS has assisted more than 1-million technicians to comply with the 1990 Clean Air Act requirements for certification in refrigerant recovery and recycling to protect the environment.

To learn more about MACS Worldwide visit our website at The MACS 2018 Training Event and Trade Show, A/Ccess will take place February 14-17 at the Caribe Royale Hotel and Convention Center in Orlando, FL. A current calendar of regional training can be found on the training page of MACS website.

Posted in #1234yf, Mobile Air Conditioning, Refrigerants, Training | Tagged , , , , , , , , , | Leave a comment