Thursday, July 30, 2015

Send Superman Over to Fix my Unit

I have noticed something that is happening now in many companies - employees are often asked to be superhuman because of the amount of work to be done and the chronic short handed situation many companies find themselves in. This can lead to looking the other way as employees do things they should not do while trying to do the impossible. I had a recent graduate complain that the company he worked for scheduled him to do an installation by himself which he did not complete until 11:30 PM. He did not even get to the job until after his normal scheduled quitting time. He had a company meeting at 7:00 AM the next morning, which he made. However, in the 7.5 hours between completing the job and returning to work he had to get home, sleep, and return to work. His truck still had the old equipment in it from the night before. He was reprimanded for having a messy truck - a violation of company policy. In my mind, the problem started when he was scheduled to do the impossible. I have heard more than one story like this. Another student told me his wife went from asking when he was going to get a job to asking when he was coming home. Upon graduating, he had responsibility for the large rack refrigeration systems in 15 grocery stores spread across 2 states. He was not left entirely on his own – they gave him a cell phone. Trying to service these far flung, complicated systems which he was just learning about had led to 60 and 70 hour weeks. Students are glad to have the job, but they are often covered up in work before they even have a year in the field. When they demonstrate that they can perform, they are rewarded with more work. I believe as an industry we need to allow new techs a bit of breathing room and time to develop into the techs we want them to be. That means we have to still provide time for education and training, time to sleep, and time to de-compress a bit. The fact that so much responsibility is being shouldered by brand new techs shows our great need. This provides opportunity for people who are looking for a rewarding career which provides the income needed for a good standard of living.  The danger we face in pushing the most promising too hard is that we could literally run our best new prospects out of the trade.  

Saturday, July 25, 2015

How Does an Air Conditioner Cabinet Become Energized?

The last two weeks I have been talking about electrical safety. Specifically, discussing the electrical hazard of an energized system cabinet. This week I would like to discuss ways that the cabinet of a system can become energized. First, for a cabinet to have a voltage other than ground, the cabinet is either not grounded, or the ground has failed. Failure to properly ground a metal cabinet is the first condition that sets up the electrical hazard. But another mistake or failed component is required to actually energize the cabinet. Some are obvious – such as a loose energized wire touching the cabinet. Others are less obvious, such as a grounded electric motor. If a motor is grounded (not shorted or open) and the equipment cabinet in which the motor is mounted is not grounded, when the motor is energized the cabinet will also become energized. Motors can sometimes be grounded and still operate. So you touch an operating unit and get shocked. Another failure that can energize a cabinet is a broken or missing insulator on heat strips. Most heat strips have one side that is wired hot all the time. If the ceramic insulators break and allow the strips to contact the frame holding them, the cabinet can become energized.

A sneaky way for a cabinet to be energized is to wire a 110 volt device into a 230 volt unit using one leg and ground. Basically, current will be going through ground anytime the 110 volt device operates. This alone won’t cause an energized case. But if the ground between the unit and the panel breaks or just gets a bad connection, now there will be a voltage between the case and the actual ground – and the case will be energized. To avoid this, don’t wire 110 volt devices this way. You either need a separate neutral AND a cabinet ground (4 wires), or you need a 230 – 110 transformer. This is why newer electric dryers have 4 prong plugs: two for the 230 volt hot legs, one for neutral for the motor, and one for a cabinet ground.

So here are a few simple rules to help you avoid creating an electrical hazard:

1. All metal cabinets and pipes should be grounded
2. Ground wires should never be used as part of an operating circuit.
3. When equipment has both 230 volt and 110 volt loads, the equipment either requires a neutral wire AND a separate ground wire, or a 230 volt to 110 volt transformer.

Thursday, July 16, 2015

Basic Electrical Safety Tips

In light of the tragic story I posted last week, I thought an article on electrical safety would be appropriate. Here are a few things we ALL should do while working on units:

Assume all units you work on are dangerous
When you inspect hundreds of units and most are safe, it is easy to assume the equipment you will be working on is safe. Don’t assume units are safe, assume the opposite. When approaching a unit, particularly one that you don’t know anything about, assume it is dangerous.

Test BEFORE you Touch
Carry a non-contact voltage detector with you at all times. Test all disconnects and units with the non-contact voltage detector BEFORE touching ANYTHING. While you may go your entire career without ever seeing an energized case or disconnect, they do occur and it only takes a few seconds to test.

All Units and Power tools SHOULD BE GROUNDED
Everything that operates on electricity should have a ground wire. The purpose of the safety ground is to provide a good path for power should electricity contact the exterior metal parts. The idea is for the ground wire to be a better path then you are. The only exceptions are double insulated tools with non-conductive cases.

You should NOT be grounded
Try to avoid grounding yourself. If at all possible, don’t lean on grounded equipment and don’t sit or stand on wet ground or pavement. The idea is to make yourself a poor path. Wearing shoes with thick rubber soles helps.

If possible, turn the power off before working on a unit
Don’t do any more live work than necessary. If you can perform the service or maintenance with the power turned off to the unit, turn the power off. Obviously this is not always possible. For example, the power must be on and operating to check the system charge.

Use only Category III or IV electric meters on HVAC Systems
That “free” meter from El Cheapo Freight is not safe to use on an air conditioning system. You have no assurance that it can withstand voltage surges. Remember, when using an electrical meter the meter quality is what separates you from the electricity you are testing – that includes the leads. They should also be rated as Category III or IV.

Always Use a Fuse Puller to Change Cartridge Fuses
Channellocks, Vise grips, and pliers are NOT fuse pullers. That bit of rubber on the grip is NOT a very good electrical insulator.

NEVER change a fuse with the circuit still energized
Removing or inserting a fuse with the circuit energized can create an arc flash. An arc flash is an electrical fireball which can hurt you even if you are not touching any energized surface.

Friday, July 10, 2015

Tech Electrocuted Changing an Air Filter

Last week I received this heart wrenching e-mail from a friend and colleague.

“Carter, I am writing you this in hope that you will pass this on to everyone.  Last week I lost a great student and a friend. He was a student that every Instructor dreams of. He was smart and eager to work hard and make a career in our field of HVAC/R.  He was only 22 years old with a wife and an 8 month old little girl. His death has really hit me hard as his instructor.  He worked for an A/C company nearby.  While working on a heat pump service call, he had been in the attic and outside to check the equipment, then he headed under the house to change the air filter for the customer. Upon touching the air handler cabinet he became locked and grounded by a wire that was shorted to the air handler’s metal cabinet.  He was wet from sweat, from being in the attic as well as outside in our hot humid air. He was LOCKED to the air handler. After some 15 minutes the home owner called him. When he did not answer, the owner went under and found him and was able to knock him off the unit and freed him. The owner then dragged him out and started CPR. EMS arrived and continued CPR on the way to the Medical Center, where medical staff also continued CPR, but a doctor pronounced him dead. Funeral services will be held tomorrow.

 I believe every class needs to tell every student and warn them of this. He was just changing an air filter, not working on the electric wiring. I know he never would have thought of being shocked by just touching the cabinet. We have all done this thousands of times, not thinking about getting shocked. TURN OFF ALL POWER before doing anything on any unit.”

How many times have you touched a unit before checking to see if the case was energized? I cannot count how many times I have done this. THIS TECH WAS JUST CHANGING A FILTER. Before touching any electrical disconnect or unit ALWAYS check with a non-contact voltage detector to make sure the cabinet is not energized. And when you work on a unit for any reason, check to make sure that it is properly grounded before you leave. Properly grounding a unit can save someone's life. It is rare for a unit cabinet to be energized – but it does happen and the results can be tragic.

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.