by Larry Brewer and the HVACRedu.net Crew
“We can only see a short distance ahead, but we can see plenty there that needs to be done.” ― Alan Turing
Winter is upon us and as professional HVACR technicians, you will need to remember all of those different little bits of information you have stored away on all of the different types of heating equipment. Here are some of the most common symptoms you’re likely to encounter when servicing heating units.
Who’s that Knocking?
On some heat pump systems, when the unit shuts down there will be a loud knocking sound that will transmit from a check valve to the refrigerant lines, making it sound as if someone is beating on a door or wall.
There are two check valves in the heat pump system, and either one of these could be the one making the noise. To determine which check valve is making the noise, some technicians will use a wooden dowel, placing one end of the dowel near the check valve and the other end on their ear. The valve making the noise will be louder than the valve not making the noise.
This knocking problem in heat pumps can be caused by non-condensables in the system. Another cause can be that after the system has been shut down for a brief time, the high and low side pressures could be near equalization. If this is the case, the liquid surrounding the ball check valve can pulse back and forth rapidly causing the knocking noise
One fix for this is to replace the ball check valve with a magnetic check valve. Some will replace the ball check valve and the expansion valve with an expansion valve that has a check valve built in. Another fix is to install a bi-directional solenoid valve in the liquid line that cycles off with the compressor contactor.
The Sounds of Water (or Refrigerant)
Some heat pumps will have a tea kettle whistling noise on start up. Some will have a noise of running water through pipes. Refrigerant is a fluid and it is normal for it to make noises when moving through piping at high velocities the same as water does. When installing the copper lines for a heat pump system, pay close attention not to allow the copper lines to touch any sheetrock walls or wall studs as this will tend to amplify the noises being transmitted through the copper line set.
Low Airflow: What Not to Do
Be sure to check for proper airflow on a heat pump system. One of the common problems associated with residential systems is low airflow. The symptoms in the cooling mode will be low superheat and low suction pressure.
Some technicians will try to elevate the suction pressure by adding refrigerant to this system. This does not fix the problem, and in fact it will compound the issue. Now we have a system that has low airflow across the indoor coil and also is overcharged. When the system is switched over to the heat mode, the indoor coil is now the condenser coil, the indoor airflow will still be inadequate, and with the system being overcharged the compounded issues will cause the high pressure switch to trip, shutting the outdoor heat pump unit off. The fix for this problem is to resolve the indoor airflow problem. Then correct the refrigerant charge.
When working with a heat pump system that has a suction line accumulator in the outdoor unit, always watch the frost line or sweat line on the side of the accumulator. Allow the unit to run long enough for all the refrigerant to boil off from within this vessel and become active within the system. In mild weather the heat pump unit may run for 5 – 10 minutes, then cycle off because the indoor air temperature has been satisfied. When the temperature is colder the unit may run for 15 to 20 minutes. In the colder weather, the longer run time has allowed all of the refrigerant to become active within the refrigerant system, and if the system is overcharged this will cause the unit to trip on high head pressure.
When servicing a unit, some technicians will watch the refrigerant pressures for five minutes, then disconnect from the system thinking all is well with the charge. If they had waited a few more minutes they would have seen the head pressure climb to a point of tripping the high pressure safety switch.
Need More Heating System Information?
HVACRedu.net offers an excellent course on Heat Pumps. Designed as an introduction to reverse-cycle heat pumps used in residential and light commercial applications, the course covers the components and operational differences of a heat pump vs. a straight air conditioning system. You’ll study components, installation, troubleshooting, and solutions. You’ll want to have a strong working knowledge of basic HVACR fundamentals prior to taking this advanced course. When you complete it, you’ll have earned 21 hours of continuing education (CEHs) applicable to NATE re-certification, and/or 10.5 BPI continuing education units (CEUs). You can purchase the course in our HVACRedu.net Online Store.
What about Gas Heat?
Working on a lot of gas heating systems? For a thorough treatment of the knowledge and skills needed to become a highly skilled technician who will install, maintain, and repair residential and small commercial Gas Heat Systems, you can enroll in our 133 HVACR Gas Heat I course. The course explores all the mechanical, electrical, and accessory devices commonly found in modern Gas Heating systems, covers fuel gas composition, electronic ignition, high-efficiency furnaces and more. With this knowledge, you can build troubleshooting skills and identify applicable codes as they pertain to the installation and use of these systems. Also extremely important is the course’s focus on safety for the technician, the building, and its occupants. Completion of Gas Heat I earns 18 hours of CEH credit applicable to NATE re-certification, and 9 BPI CEUs.
Toughen up on Troubleshooting
For a focused refresher on combustion-related problems in gas and oil heating systems, take this Troubleshooting Combustion module. The function and proper use of tools used for effective combustion analysis is also discussed. Alternately, our Combustion Safety, Testing & Analysis module, covering the application of those concepts in modern HVAC systems and equipment might be just the information you need to level up your skills this winter.
Whatever you decide to learn, we encourage you to learn something heading into this winter season. And if we can help you buff up your skills, update your knowledge or answer any questions, please contact us and we’ll be happy to talk with you.
“If we let ourselves, we shall always be waiting for some distraction or other to end before we can really get down to our work. The only people who achieve much are those who want knowledge so badly that they seek it while the conditions are still unfavorable. Favorable conditions never come.”
― C.S. Lewis