Saturday, July 4, 2015

Checking Thermal Expansion Valves

If you work on air conditioners you have heard about the thermostatic expansion valve problem be-deviling the industry right now. A relatively small detail in the manufacturing of a widely used compressor has caused massive problems throughout the industry. For many years the best advice regarding service on TXVs was to leave them alone. They very rarely gave problems, and messing with them was more likely to cause a problem than solve one. Unfortunately, TXV problems have become very common now.

Valves manufactured by all suppliers are sticking due to a chemical reaction to a rust inhibitor that was used on one part inside scroll compressors. Most of the time these valves will underfeed. A system with a valve that is clogged with goo will operate with a low suction pressure, a somewhat low high side pressure, and a high superheat. It can look like an undercharge. However, an undercharged system will have low or no subcooling while a properly charged system with a clogged valve will have a normal to high subcooling. The subcooling is really the key to telling the difference between an undercharged system and an underfeeding valve. If you suspect a clogged valve, be sure to check for other refrigerant restrictions – such as a clogged filter drier. Of course if you change the valve, you will also want to change the filter.

A valve that has lost its bulb charge will also underfeed, but these normally are drastic – with the low side pulling down close to 0 psig. Valves can lose their charge from improper installation. If the bulb is attached to the suction line near where the suction line is brazed in and you don’t protect it from heat, the bulb pressure can pop the bulb charge.

Overfeeding valves are normally due to misapplication or poor installation. A system with an overfeeding valve will have a high suction pressure, a low superheat, and a low subcooling. If you see this, check the bulb installation. Make sure it is making good contact with the suction line and is well insulated. Also, make sure the external equalizer comes off the top of the suction line, not the bottom.

Unfortunately it is no longer true that expansion valves rarely mess up. However, checking the valve installation and system subcooling may save you a bunch of time and trouble. It takes far less time to check system subcooling, superheat, and the valve installation than it does to change a valve.    

Monday, June 29, 2015

Stay Hydrated and Cool

When it gets really hot, evaporation of sweat is all that stands between you and heat exhaustion. That is really your ace in the hole. The body perspires and the sweat evaporates to cool you off. When you are working in a hot environment you sweat a great deal – and that is good. However, it is important to replace the water. That is why you should have lots of water available and drink water continually while working.

Weather conditions can play a big part as well. A relative humidity over 60% (pretty much all summer in Georgia) slows the evaporation process, increasing the likelihood of heat exhaustion. When the heat index exceeds 90, you need to be careful. When it exceeds 100, you need to be extra careful. Besides hydration, stay out of direct sun and seek cool shelter whenever possible. Time spent in attics should be limited and preferably only in the early morning or evening.
  
Failure to drink enough water can lead to dehydration. Failure to stay hydrated and cool can lead to heat exhaustion, which can be dangerous. If you continue to ignore your body’s warning signals, heat stroke can occur, which is a medical emergency. You are no help to anybody passed out somewhere. If you are thirsty and really tired – TAKE A BREAK AND DRINK SOME WATER! Finally, note that we are drinking water; NOT beer or caffeinated soft drinks. Symptoms of dehydration, heat exhaustion, and heat stroke are listed below.

Symptoms of dehydration include:
fatigue
loss of appetite
flushed skin
heat intolerance
light-headedness
dark-colored urine
dry cough  

Symptoms of heat exhaustion include:
Confusion
Dark-colored urine (a sign of dehydration)
Dizziness
Fainting
Fatigue
Headache
Muscle or abdominal cramps
Nausea, vomiting, or diarrhea
Pale skin
Profuse sweating
Rapid heartbeat

Symptoms of heat stroke include:
Throbbing headache
Dizziness and light-headedness
LACK OF SWEATING DESPITE THE HEAT
Red, hot, and dry skin
Muscle weakness or cramps
Nausea and vomiting
Rapid heartbeat, which may be either strong or weak
Rapid, shallow breathing
Confusion, disorientation, or staggering
SEIZURES
UNCONSCIOUSNESS

Friday, June 19, 2015

Grounded Compressor Behavior

Typically, a grounded compressor does not really do anything – that is the compressor does nothing. The breaker, or fuse does plenty. Normally the breaker trips and/or the fuse blows as soon as the compressor is energized. In the case of many units with single pole contactors, the breaker may trip and/or the fuse blow as soon as power is turned on to the unit – even if the contactor is not closed. This is because power from one leg feeds the compressor and condenser fan motor all the time. If that leg of power is grounded, the breaker will normally trip immediately.

Occasionally a grounded compressor can cause the condenser fan motor to run slowly all the time. The fan gets one leg of power all the time. If the leg of the compressor that is fed by the normally open pole of the contactor is grounded, that provides a path for the current, causing the fan motor to receive close to 120 volts. With these units, the breaker does not trip until the contactor closes. I have even seen compressors which had a high resistance ground operate, even though they were grounded. If the ground is hundreds, or thousands of ohms, the current passing through to ground will not be enough to blow fuses or trip breakers. This type of ground is most often caused by system contamination creating a path inside the compressor shell.

The other day I experienced a type of grounded compressor which I had not seen before. When I arrived, the compressor would try to start for several minutes, and then the breaker would trip. The fan would run and the compressor would hum. Immediately I thought “capacitor.” But the capacitor checked out. So did the wiring. I then decided to check the amp draw to the compressor. On L1 the amp draw was 0, yet I could hear the compressor humming. I looked at my meter to make sure I had it set correctly and that it was not on hold. Then I decided to check the amps on L2, and read 65 amps. This is a single phase motor. Where are the amps going? Finally, I checked the amp draw on the bonding ground wire and read 24 amps. Current was travelling from L2 to ground – indicating a grounded compressor. The fact that not all of the current was travelling through the bonding ground concerned me, so I turned off the breaker. I then verified that the compressor was grounded by ohming it out. I was there for a second opinion, and I verified that the compressor was dead. I also advised the owner against trying to operate the unit any more, explaining that current traveling through ground is dangerous.

Wednesday, May 20, 2015

Rees Scholarship Deadline Approaching

I have mentioned the Rees Scholarship in the past. Now is the time to encourage deserving students to apply. Copied below is a letter from Misha Adams of AHRI explaining a bit about the scholarship and how to apply.

Our July 1 fall scholarship deadline is approaching quickly!
The Rees Scholarship Foundation has awarded nearly $335,000 to 195 students enrolled in HVACR programs nationwide since 2003 – and we would like to expand our reach.
The Clifford H. “Ted” Rees, Jr. Scholarship Foundation was established to assist with the recruitment and competency of future HVACR and water heating technicians by awarding up to $2,000 to qualified students enrolled in an accredited school. The Foundation awards motivated students with a genuine interest in the HVACR and water heating field, helping some of the most promising candidates to successfully enter the industry.
This year, the Rees Scholarship Foundation would like to award more scholarships than the 43 scholarships we provided last year, and we need your help.
We truly believe instructors and staff play an essential role in not only educating and motivating students, but assisting them in finding opportunities to help them complete their education successfully. The numbers support this: Over 70 percent of our past applicants learned about Rees from their instructors. With that in mind, we would like to provide you and/or your school’s HVACR department with resources about Rees you can give to your students. These include brochures, flyers, and posters for the classroom. 

Brochures and flyers are also available for download at  http://reesscholarship.org/site/311/Schools/Resources

To learn more about the Rees Scholarship and the submission process, review our FAQ  at  http://reesscholarship.org/site/314/Apply/Frequently-Asked-Questions

Download an application at

Please encourage your students to apply!
Feel free to reach out to me directly as well should you or your students have any additional questions. Also, please feel free to forward this message to your HVAC department colleagues and/or related staff members.

Sincerely,

Misha Adams
Rees Program Specialist
Air-Conditioning, Heating, and Refrigeration Institute
2111 Wilson Blvd, Suite 500
Arlington, VA 22201
Phone: 703-293-4839
E-mail: MAdams@ahrinet.org


Monday, May 18, 2015

Cleaning Condensate Lines















In the southeast, it is a given that the evaporator condensate line will get clogged with slime. The only questions are how long will it take and how messy will it be to clean up? What we often did in the past was to cut out the section of drain near the coil, blow out the drain line, and rebuild the drain with new PVC ells and pipe. However, that means the owner is constantly paying for you to rebuild something that should be cleanable. That is why every evaporator condensate line should have a way to open the drain to facilitate cleaning. In fact, this is now required in the most mechanical codes. You can add cleanout spots by replacing ells with tees, or by using a manufactured product made just for that purpose. Rectorseal and MSD Research both market drain cleanout devices which make complying with the mechanical code and cleaning the drain easier. Ideally, you should be able to clean out the line in both directions – from your cleanout to the evaporator and from your cleanout to the outside.

A Gallo gun using CO2 charges works well for blowing out the drain line. Nitrogen does a good job too, but getting a nitrogen cylinder to the cleanout spot can be difficult. Another option is a sludge sucker. It uses nitrogen to create a vortex, which sucks the condensate and goo out of the drain line. The sludge sucker typically connects to the drain outlet. Some techs use wet vacs and connect to the drain outlet, or to points on the condensate cleanout. Even if the drain is not stopped up, clearing the evaporator condensate line should be part of normal service. Don’t make the customer call you back later because the condensate line plugged up.






Sunday, May 10, 2015

Pot Use Cuts Career Short

There is lot of press these days about marijuana becoming more widely accepted. However, you should be aware that marijuana use can have a very negative impact on your career. Employers can legally refuse to hire people who test positive for marijuana use. Many employers require drug tests for prospective employees, some use random drug tests on current employees. Since these tests can detect marijuana in your system for up to a month after using it, you basically need to not use it – even on your own time. I am writing about this topic because it has recently cut short the career of a promising student. He graduated and got a job in the field working with a good company. He was excited to get the job, and the company was happy to have him. He seemed to be working out – everyone was happy. Then he failed the drug test. End of job. The student really needed the job. The company was disappointed because they needed the help. However, they can’t afford to keep him. Their insurance won’t allow it. This is not just about someone’s idea of morals or right and wrong, it is about common sense. People who are not in full command of all their mental faculties should not be working around high voltages, driving, using torches, or any number of other potentially dangerous things air conditioning techs must do. There may be some companies that are OK with drug use – generally speaking these are not good places to work. First, they know you can’t get a job elsewhere, so the pay is low. Second, do you really want to work in a potentially dangerous field around a bunch of people who may not be fully conscious? Even if you don’t blow yourself up while you are high, the guy next to you might. If you want a full, productive career – stay clean.

Saturday, May 2, 2015

Mission HVAC


Shuretape has launched an initiative to follow three students at Athens Technical College through their studies in the Air Conditioning Technology Program. To support the students, Shurtape is challenging them each to a series of missions. They complete the mission and report their findings on the Shurtape blog. They have chosen three students with different backgrounds and different ages: Matt Morris, Daniel Buth, and Josue Treo. By following these three students’ blog postings, you can gain some perspective on what it is like to be an HVAC student preparing to enter this profession. They receive a new mission every month. The best way to find out more about these three outstanding students and their mission is look at the Shurtape blog http://www.shurtape.com/blog