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.  

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.

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.

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.

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.