In this final installment, I’d like to offer some advice on how technicians can work safely with compressors, electrical systems, and walk-in freezers.

Compressor Startup

On starting a compressor, it is recommended to stand clear from a direct line of the compressor heads on a non-hermetic-type unit. Why? The piston valve plate clearance is measured in thousandths of an inch and is usually determined by the

valve plate to compressor body gasket thickness.

If you ever ran a compressor with the heads off at 1,725 rpm, the speed of the pistons creates a blur and should be respected. It’s rare, but compressor assembly errors have occurred. An object left above a piston cavity can be disastrous.

Many years ago I was starting a 75-hp open-type compressor and immediately noticed how quietly it ran. The pressures were equal on the high and low sides, and the amperage of the compressor motor was very low.

Upon removal of the compressor heads, however, it was found all the pistons were missing! (This is a true story and quite embarrassing, since I was the manufacturer’s representative.)

Disassembly of the compressor head, cover plates, and anything requiring bolt removal, requires careful disassembly. You always loosen the bolts and then gently pry the head, valve, or cover plate from its seat.

There are good reasons for this procedure:

  • There may be internal pressure existing within the system.

  • If the object being removed is heavy, it could slip off and cause injury.

The same procedure applies to heavy flywheel or pulley removal. Make sure the object is loosened from its seat before removing the nuts or bolts completely.


The most common error made by technicians in the field is to turn off the wrong disconnect switch. The higher the voltage, the more serious the results.

Always check the circuit you are about to work on with a volt meter to be certain the power is off!

The most serious mistake made would be to jumper the fuses and turn the power on. It is possible to black out an area for three square miles instantly. The reasons are complicated, but it has happened.

Don’t ever manually close a compressor contactor under any condition. I have seen a national service manager do just this in my presence. The results could be devastating. Furthermore, don’t close any contactor manually.

Say you arrive at a jobsite and are told two sets of fuses were replaced, and they didn’t know why; they just blew. The customers then ask if you wish to see a third set blow out to demonstrate what happened. Of course you say no, and find the short.

The damage caused, particularly to a compressor with a shorted motor winding within the system circuit, has created a compressor replacement and a lengthy chemical cleanup of the whole system.

A common occurrence of electrical shorts is due to vibration. All motors tend to have a high-frequency vibration which affects the wiring connections.

The problem area in the electrical circuit is loose screws, wire nuts, and wire lugs. It should be the technician’s job to check all electrical screws for tightness on every visit to the jobsite.

I had a habit of wrapping electrical tape around all wire nuts so they would not drop off from vibration. Another reason I do this is to see if others have worked in this area. Very few technicians take the time to complete this step.

Removing heavy unit panels should be done with a helper to avoid broken toes and other injuries. On certain jobs, gloves should be worn to prevent cuts or burns to the hands. A first aid kit should be in your vehicle with the usual items, such as Band-Aids, gauze, aspirin, burn ointment, and tweezers for splinters.

Any time you are working in a hot enclosure, provide fans for air circulation and take occasional breaks to prevent dehydration. Drink lots of water.

Suits are provided today with ice packs or actual air-cooled ones, similar to those worn by the astronauts for these most uncomfortable working conditions.

Low-Temperature Walk-In Freezers

Whenever you have the occasion to work on this type of equipment, it’s probably in the summer. Keep a winter jacket, wool hat, and gloves in your vehicle for this purpose.

Not all the cold storage installations have means of quickly exiting these quarters. I have seen telephones, buzzers, axes, and TV monitors placed within freezer compartments.

Regardless of the protection, nothing matches someone standing directly outside the door for any emergencies. I have been locked in a “safe” freezer, and will never have it repeated.

In your travels from job to job, you do encounter customers who will want you to break the rules in order to get them on-line as soon as possible.

In most cases, it is someone who does not have a maintenance contract, and waits until his unit fails.

He will tell you that if any damage is caused, he will be responsible. Don’t believe it! There have been thousands of lawsuits and the customer will win the case because of negligence by a technician.

Even if you have him put this in writing, your company will still lose the suit. Why? The technician is the expert and knows better, as the judge will state.

My motto is, “Take your time and do it right.” If you work for a company that allows you to “overlook” these discrepancies, consider working for another company.

From working with hundreds of hvacr contractors across the country, I have found 98% do follow the rules to the letter. Use your knowledge, stay alert — and be safe.

John C. Schaub is president of Schaub Consulting. He has been involved in hvacr as a field engineer and company owner for more than 40 years, and has worked on 35,000 jobsites. For more information, contact him at 609-654-2138; www.chillers. com (website).