In this column, Jim Johnson, director of training for Technical Training Associates, presents a specific HVACR equipment problem and invites readers to submit their diagnosis. From those who submit the correct answer by the stated deadline, there will be a prize drawing. The answer, and the prize winner, will be announced in the next column, along with another problem for you to solve.

SOLUTION TO OUR LAST PROBLEM

Enlarge this picture Figure A. (Click on the diagram for an enlarged view.)

We begin this edition with the answer to our “An Older Gas Furnace That’s Blowing Cool Air” problem presented in the Oct. 8, 2007 issue.

The failed component was the transformer. A reading of 120 VAC at the PR-1 and PR-2 connections and a 0-VAC reading (which should have been 24 VAC) at SEC-1 and SEC-2 proved the component failure.

Enlarge this picture Figure B. (Click on the diagram for an enlarged view.)

In regard to the second part of our troubleshooting question, the reason the fan motor was running constantly was due to the loss of 24-VAC applied to the 2A coil (shown in the partial diagram of the control circuit in Figure A), which allowed the normally closed 2A contact (shown in the partial diagram of the operating voltage segment of the schematic in Figure B) to remain closed constantly. In an off cycle, the 24-VAC control system constantly complete to the 2A coil will keep the N.C. contacts open until a call for heat, which along with the time delay system breaks the 2A coil circuit, de-energizing the coil, and allowing the contacts to close and create the complete circuit to the low speed winding of the blower motor.

From those readers who sent in the correct diagnosis, the prize drawing winner is Ed Herget.

And, now on to this issue’s problem.

AN ELECTRIC HEATING SYSTEM THAT’S NOT HEATING ENOUGH

Enlarge this picture Figure 1. (Click on the diagram for an enlarged view.)

In this troubleshooting scenario we’re dealing with a resistance heating system, and the customer has called to say that the unit is no longer keeping them warm “like it used to.” This particular unit, which can be used in conjunction with a heat pump, or only as an electric furnace, is not paired with a refrigeration system. It has been in service for several years with no previous service calls.

When you arrive, you note that the temperature in the building is mildly chilly, and that the air handler motor is operating on low speed. The thermostat is set to call for heat, but the temperature rise is insufficient. Removing the access panel of the unit, you locate the schematic diagram (shown in Figure 1) and begin your troubleshooting process with a voltmeter.

Noting that the three heating elements (HE1, HE2, and HE3) are controlled by two relays (HR1 and HR2), and that a limit control (LC1, LC2, and LC3) is wired in series with each element, you get the following readings:

1. 240 VAC at the terminal connections for HE1.

2. 240 VAC at the terminal connections for HE2.

3. 240 VAC at the terminal connections for HE3.

When testing the circuits with a clamp-on ammeter, you note:

1. 0 Amps on the wiring connection to HE2.

2. 0 Amps on the wiring connection to HE1.

3. The manufacturer’s listed current draw on the wiring to HE3.

And your troubleshooting question is: What needs to be done in order to get this unit operating normally again?

If you have the answer to this question, click on www.technicaltrainingassoc.com and submit your diagnosis via The NEWS link. All correct answers received by the deadline of Dec. 28, 2007 will be entered into a prize drawing for a Fieldpiece SC46 Clamp-on Digital Meter. The correct answer to this question, along with the results of the drawing, will be published in the Feb. 4, 2008 issue.

Publication date: 12/03/2007

The first Copeland Scroll® rolled off the production line in 1987, and the cooling industry was changed in a way that would benefit contractors and their customers in many, many ways. The prime benefits have been efficiency and product reliability.

Many features of the Scroll focus on preventing compressor failures, but the Scroll’s primary design also improves efficiency and reliability thanks to its classic, concentric compression scroll, in which one spiral-shaped part fits into another; the space between the two parts contains crescent-shaped gas pockets.

CLASSIC SCROLL OPERATION

In operation, one Scroll is fixed in place while the other orbits within the first. The refrigerant gas is drawn in by the movement and forced toward the center of the scroll through successively smaller pockets, thereby increasing the gas pressure until it reaches its maximum pressure. Then it’s released through a discharge port in the fixed scroll.

Copeland Scroll compressors are unique in the industry because they feature both axial and radial compliance in their design, whereas other scroll models utilize a mechanically fixed design and scroll tip seals.

Axial compliance refers to the ability of the scrolls to separate in the axial — or vertical — direction remaining in continuous contact around an axis, in all normal operating conditions, ensuring minimal leakage without the use of tip seals. Radial compliance refers to the ability of the scroll flanks to separate. These features of the Scroll design allow the compressor to be more tolerant of liquid refrigerant or debris than other technologies, making for a compressor that is extremely durable and reliable.

The combination of axial and radial compliance means that Scroll compressors actually “wear in” rather than wearing out. Continuous flank contact, maintained by centrifugal force, also minimizes gas leakage and maximizes efficiency of the compressor.

Next month: Tech Tips will begin examining the Scroll’s improved reliability through its oil control system.

For more information, click on the Emerson Climate Technologies logo above.