Fundamentals: After the Storm

The diagnosis and repair sequence:

The manager at a sales outlet advises the contractor that everything was working great until the last storm.

“We’ll get right on it,” the technician tells the manager.

The technician tells the apprentice, “Now listen, we have to go up on the roof. Bring the truck around back and set up the ladder. I have to check the circuit breaker inside.”

When the technician comes outside, he asks the apprentice a series of questions as a means of starting his training in the hvacr industry. He starts off with the proper safety setting of an extension ladder.

Technician:

“How many feet do you think the top of the ladder should be extended above the roof?”

a) The top doesn’t need to extend above the roof.

b) The top should be even with the roof edge.

c) The top should extend 2 rungs above the roof edge.

d) The top should extend 3 feet above the roof edge.

Answer:

d The top should extend 3 feet above the roof edge.

Technician

“That’s correct. It’s a good practice to make sure that you always set it that way for your safety. By having it that high, you will have a firm handhold for when you get off the ladder onto the roof.”

Technician:

“Let’s head up and look at the system.” The recruit picks up the toolbox and heads for the ladder.

Technician:

“Hold it. How are you going to climb the ladder with the toolbox in your hand?”

a) I’ll put it on my shoulder and use one hand.

b) I’ll carry it by the handle and use one hand.

c) I’ll move it up one step at a time while I hold on with the other hand.

d) We’ll pull it up with a rope.

Answer:

d) We'll put it up with a rope.

Technician:

“Correct. We have to work safely and it is important to keep both hands on the ladder. I’ll climb up with a rope tied to my tool belt. Then I’ll drop it to you and you can tie on the toolbox. After I pull the toolbox to the roof, you climb the ladder. Make sure you watch how I climb so you can do the same thing.”

Technician:

“Come on over to the unit and we’ll start checking it out.”

Apprentice:

“If this equipment is anything like electronic equipment, then the storm last night might have blown a fuse.”

Technician:

“Good analysis. I found the circuit breaker tripped while you were setting up the ladder. I reset the breaker so let’s see if the unit is operating properly. Well, the blower is operating but not the compressor. Any ideas?”

Apprentice:

“Let me look at the nametag before I say anything. This is a three-phase system, but only the compressor shows to be three phase. I think I know. The problem is:

a) Nothing, power is properly applied.

b) At least two fuses are blown.

c) At least one fuse is blown.

d) The circuit breaker isn’t supplying the full voltage.

Answer:

c) At least one fuse is blown.

Technician:

“Let’s check the fuses and make sure. You’re right. One fuse was blown. We’ll replace it and make sure everything is running the way it should.”

Apprentice:

“Looks like we have more of a problem. The compressor is still not running.”

Technician:

“What are we going to look at next?”

Apprentice:

“Well, I know the unit is turned on and calling for cooling. I also know that the fuses are good. I think I would see that we had:

a) Voltage at the compressor terminals.

b) Resistance at the compressor terminals.

c) Continuity at the compressor terminals.

d) Ohms at the compressor terminals.

Answer:

a) Voltage at the compressor terminals

Technician:

“As a novice in the hvacr industry, your previous experience in electronics is going to be very helpful. That is just what I would do. We have the proper voltage at the compressor terminals.

What test should we do next?”

a) Shut the unit down at the disconnect, and check for full power at the compressor terminals with the wires properly connected.

b) Shut the unit down at the disconnect, remove the power wires from the compressor terminals, and check for equal resistance readings across the windings.

c) Shut the unit down at the disconnect, remove the power wires from the compressor terminals, and check for unequal resistance readings across the windings.

d) Shut the unit down at the disconnect, leave the power wires connected to the compressor terminals, and check for unequal resistance readings across the windings.

Answer:

b) Shut the unit down at the disconnect, remove the power wires from the compressor terminals, and check for equal resistance readings across the windings.

Apprentice:

“That type of check will tell us if the compressor windings may still be good, but only after we wait until the compressor cools off. The internal safety is probably open due to the compressor not having the proper power on all three power lines.”

Technician:

“The compressor is cool enough. Turn on the power. Great, the compressor is running. Let’s check out the rest of the system operation to make sure everything is working, and then we’ll let the manager know.”