The problem:A service call for a second opinion about replacing the condensing unit.

The apprentice: Graduate of a vocational school.

The technician: Highly qualified with 10 years of experience.

The diagnosis and repair sequence:

The technician has completed discussing the cooling system with the customer. His conversation came up with the following facts:

  • Another company checked the system about a week ago.
  • The customer described the other company’s technician as very young looking.
  • The customer said the previous technician stated that the unit needed to be replaced because it was old and the blower fan on the outdoor unit was running slow.

    • The technician and the apprentice examine the existing unit.



    Technician:

    “So, the previous technician said that the unit was too old. Is there a way to accurately determine the age of a unit?”

    Apprentice:

    “Yes, by…”

    a) Seeing how much rust falls off the unit.

    b) Counting the number of fan blades on the condenser fan.

    c) Determining number of fins per inch on the condenser.

    d) Checking the model and serial numbers with the manufacturer’s rep.

    Answer:

    d) Checking the model and serial numbers with the manufacturer's rep.

    Technician:

    “Now let’s look at what is too old. Do you think there is a way to figure out if this equipment is too old?”

    Apprentice:

    “Sure, I would look at the SEER rating.”

    Technician:

    “What is SEER?”

    a) Seasonal Energy Efficiency Ratio

    b) Sectional Energy Efficiency Ratio

    c) Semi-annual Energy Efficiency Ratio

    d) System Energy Efficiency Ration

    Answer:

    a) Seasonal Energy Efficiency Ratio



    Technician:

    “What would the SEER rating tell you?”

    a) Energy used per year compared to the energy used per minute.

    b) Total cooling capacity per year compared to energy used per year.

    c) Total heat capacity per year compared to total cooling capacity per year.

    d) Cooling capacity per year compared to the unit size.

    Answer: b) Total cooling capacity per year round compared to energy used per year.

    Apprentice:

    “And the comparison gives you a ratio number that you can use to compare equipment, so if I know the SEER of an existing unit and compare it to a newer unit, I would be able to start to determine if it is too old. In class, we had to read about the changes that are being proposed about the SEER of equipment. New units in the future may be required to have a minimum SEER of 12. The older unit standard was 10 SEER, and previous minimum standards were as low as 6 or 8.”



    Technician:

    “Your instructor really keeps his students up to speed on current trends in the industry. So, is this unit too old?”

    Apprentice:

    “I can’t determine that until I obtain all the equipment information and call the distributor.”

    Technician:

    “Unfortunately, we don’t have time to do that. Let’s start the system up and check out the operation. Look at the operation and tell me what you think.”

    Apprentice:

    “From what I can see, and what I was taught, on a day like today with the temperature around 65°F the head pressure for R-22 should be around…”

    a) 200 psig

    b) 165 psig

    c) 235 psig

    d) 65 psig

    Answer:

    b) 165 psig

    Technician:

    “Good observation. Then can you tell me why it is running higher than expected?”

    Apprentice:

    “Sure, the condenser fan is running slow. That was the reason the previous guy gave for saying the unit needed to be replaced.”

    Technician:

    “Is the fan motor really bad?”

    Apprentice:

    “I’m not sure. I think I should check the system to see if it is possibly a multi-speed motor.”

    Technician:

    “Check away.”

    Apprentice:

    “The wiring diagram (below) shows that there is a control in the circuit of the condenser fan and it shows that the motor is at least two speed.”

    Technician:

    “What operates the control?”

    a) Time of day

    b) Temperature

    c) Season

    d) Degree days

    Answer: b) Temperature



    Technician:

    “Is that the only thing that can control the fan speed?”

    Apprentice:

    “Absolutely not. Pressure can be used also to control the speed. By controlling the speed of the fan, the system can raise and/or lower the head pressure depending on the outside ambient temperature. This helps to make the system more efficient.”

    Technician:

    “Well, let’s finish checking out the system. You take down the model and serial numbers. Call the supply house and determine the age and SEER of the system so we can properly advise the customer. I’ll check to see if raising the temperature of the condenser fan control will have the fan run at a different speed. Maybe this unit isn’t as old or inefficient as the other guy thought.”

    Publication date: 05/28/2001