How to Determine and Overcharged Unit with a TXV

This quarter’s Tech Tip is brought to you by Allied Air.

When a unit is slightly overcharged with a TXV metering device, both suction and superheat may appear normal but the performance and efficiency are diminished. These conditions are caused by the TXV as it meters refrigerant flow into the evaporator and excess charge is stored in the condenser. If excess charge levels are extremely high, this elevates the head pressure and liquid sub-cooling levels. If the charge is high enough, the suction pressure may be high with low superheat present.
When charging R-410A systems, always charge as a liquid and follow the procedure below:
•  Operate unit a minimum of 10 minutes before checking charge..
•  Measure liquid service valve pressure by attaching an accurate gage to service port.
•  
Measure liquid line temperature by attaching an accurate thermistor type or electronic thermometer to liquid line near outdoor coil.
•  Calculate subcooling (saturation temperature—measured temperature) and compare to table on back of control box cover
.
•  Add refrigerant if subcooling is lower than range shown in table. Recover refrigerant to decrease subcooling.
• 
 If ambient temperature is lower than 65°F, weigh refrigerant according to the nameplate data.

As always, if you need assistance with charging please feel free to contact the Famous Supply Technical Services Department.

Jeff Rosenblum
Technical Support
19 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

How safe is the home that you’re entering

Hello all! I have a question. How safe is the home you are entering and how safe is that home when you leave? Do you know?

So, what exactly am I taking about? Carbon monoxide. We are in the heating season now and unfortunately we are going to hear stories on the news about CO poisoning. This is an ongoing issue and we hear about it every year. There are too many stories of families, businesses and daycares having CO issues. One story that comes to mind was from a few years ago. There was a daycare in the basement of a church. The boiler was having issues and was causing CO levels around 400ppm in the air. The teachers noticed a problem when all 20 kids were getting sick and so were the adults. Was the CO level of this boiler ever checked?

Now we all know that CO is a product of incomplete combustion. But how do we know if it’s incomplete? We’ve all probably heard that if the flames are blue then it’s burning clean. That is a pure myth. We cannot judge the safety of the equipment based on the color of the flame. We must test it!

In order to test it you need to use a combustion analyzer. There are several on the market right now. By utilizing a combustion analyzer we can determine CO, O2, CO2, flue temp and efficiency and much more. In this day and age we simply cannot guess. We must test! By testing the equipment, we can determine if there are any potential safety concerns. Now you can feel better that at the time you leave, the equipment is running correctly.

So what is correct? We like to see CO levels no higher than 100ppm undiluted and stable. Lower levels are always better but we need to make sure it is stable. This is just the beginning of combustion testing but a good starting point. As a note: CO should be tested in the equipment, undiluted, not in the air. Testing for CO in the air has its merits but often leaves potential issues unseen.

So going forward lets make sure we are well equipped this winter and we test everything.

If you need any additional info please don’t hesitate to call the Famous Supply HVAC Tech Dept. Have a safe winter!

Jeff Rosenblum
Technical Support
19 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

Air Conditioner Terminology

Hello all! It seems that the air conditioning season is upon us (finally)! As such, I figured this would be a good time to review some AC terminology. As always, if you need
any help please feel free to call the Famous Supply Tech Support Department at 330.475.8230.

  • Superheat: The amount of heat added to a substance above its boiling point. Superheat happens in the evaporator. Once the refrigerant boils o , it continues to absorb heat.
  • Subcooling: The amount of heat removed from a substance below its dew point. Subcooling takes place in the condenser. As the refrigerant condenses, it continues to be cooled o below its dew point.
  • Metering Device: This causes a drop in refrigerant pressure. When we drop the pressure of refrigerant, the temperature also drops. We use this idea in order to absorb heat from the house. Typical metering devices include the TXV, piston (fixed bore), capillary tube, and LEV.
  • Compressor: This is what raises the pressure of the refrigerant. When we raise the pressure, we also raise the temperature. We raise it above the outdoor ambient temperature so we can use the outdoor air to cool the refrigerant and provide subcooling.
  • Temperature Drop: This is the return air temperature minus the supply temperature.
  • Accumulator: This is sometimes used in air conditioners to capture any liquid refrigerant that may make its way back to the compressor. Liquid can cause damage to the compressor.
  • Crankcase Heater: This is sometimes added to an air conditioner. The purpose of this is to keep the compressor warm to avoid refrigerant migration in the oil. When refrigerant
migrates into the oil and the compressor starts, it causes the coil to foam. This provides inadequate lubrication for the compressor.

Jeff Rosenblum
Technical Support
17 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

Why Do Evaporator Coils Fail?

We have all seen or diagnosed a bad or poorly performing evaporator coil. Over my years in the eld, I have diagnosed bad coils and the reasons why they fail can be surprising. So why do they fail? Here are a few things we have seen.

Coil plugging. When filters are neglected, the dirt can bypass the filter and plug up the evaporator coil. This will restrict the airflow and cause poor heat transfer. How do you combat this problem? Maintenance and proper filter design will usually solve this. Change the filter often, make sure it is sized correctly and the static pressure drop is not excessive, and verify there is not air bypassing the filter.

Vibration. If the coil is sitting on top of an air handler and the blower is out of balance, the vibration can cause the coils to crack and fail. Make sure there is not excessive vibration being transmitted through the system.

Corrosion. This has been a big one lately. We all hear about corrosion of coils. This
 is a big reason why they fail. Sometimes, if the coil is in a corrosive environment, a coated coil may be needed to resolve this. Look at where this system will be installed and take the necessary precautions.

Freeze ups. Allowing the coil to freeze and thaw and freeze and thaw several times can cause failures with the coil. I always tell people that if ice can move a mountain it can crack a coil. Make sure the refrigerant charge is correct and most importantly, the airflow is right.

System Design. If the system was never properly designed right in the first place, or the wrong coil was chosen for the application, you can expect the coil to fail well before its time comes.

So these are 5 reasons why a coil can fail. As always,
if you have any questions please feel free to contact the Famous Supply HVAC Tech department.

Jeff Rosenblum
Technical Support
17 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

Test in-Test out

When I started in the HVAC industry, I was taught a method of testing that has served me well for several years. It’s called “Test in-Test out”.

What exactly is Test in-Test out? When diagnosing an issue with the equipment, many times we make changes and head on to the next job. How do we know
if the changes we made actually made a difference? Use the procedure of Test in-Test out. When you originally diagnosed the equipment you had a certain set of readings (pressure, voltage, etc.). Once you perform the needed changes, retest everything and compare your readings. Did anything change? If not, then the problem may not be completely resolved.

Here’s an example: If you check a pressure switch because it is not closing, you may find out that the inducer is only pulling .3”
wc, and the switch needs .9” wc to close. You look
deeper into the system and realize that there is a dip in the exhaust pipe that is collecting water. Once the repairs are made and the system is back in operation, retest to verify that the repairs you made have significantly changed your readings.

Using this procedure will give you and your client peace of mind that you did everything to resolve their issue.

Jeff Rosenblum
Technical Support
17 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

Combustion Testing and Why It’s Important

As you may have noticed, there has been a slight chill in the air. Sorry to be the bearer of bad news, but you all know what that means… furnace season is upon us. With the furnaces starting to be put into service, we need to be certain that they are operating safely. The annual tune up just isn’t complete without a combustion test.

Why is it so important to test the combustion of the equipment? Well, without testing, we cannot tell the homeowner that the furnace is safe at the time of service. Above anything, we want to be sure that the homeowner feels comfortable that their equipment is safe and efficient.

There is no better tool than a Combustion Analyzer. With the analyzer, we can test CO, CO2, O2 flue temperature, draft and several others. The tests can also help in diagnosing a bad
heat exchanger. The homeowner trusts us as technicians to be able to detect whether their furnace is functioning correctly and that it is safe to operate, and based on the readings taken with the combustion analyzer, we can do our part in making a homeowner feel safe, which is one of the best things we can do.

Jeff Rosenblum
Technical Support
16 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

How to Improve Your Mitsubishi Troubleshooting

Hello Everyone! Mitsubishi makes some of the most efficient and comfortable systems available. If you have ever installed a Mitsubishi unit, then you know it is a pretty easy task. However, it seems that when it comes to diagnosing a problem with the units, many techs shy away from them. So, how do you go about diagnosing a system that you are not familiar with?

Have you heard of Mitsubishi’s website, www.mylinkdrive.com? With this site, you can find specs on the equipment, advertising info, product matchups, and service manuals. There is also an incredibly helpful tab called ‘M&P Troubleshooter’, which provides you with a step-by-step diagnosis for the exact system you are working on. All you have to do is follow the instructions step-by-step, and it will give you the necessary information to properly diagnose the system.

As always, if you need any assistance, please feel free to contact the Famous Supply HVAC Tech Department at 330-434-5194.

High Head Pressure on Heat Pumps

Diagnosing a heat pump that is tripping on high head pressure in heating mode can be a challenge. With three service ports to choose from and many different “valves” and metering devices, it can be difficult to narrow down what exactly is causing the system to trip.

  1. Verify that the system is listed through AHRI as a viable match. This is especially important on newly installed equipment. An undersized indoor coil can cause the system to run high head pressure.
  2. Check airflow at the indoor unit. This can be verified by measuring the static pressure on the duct. Restricted airflow/a dirty coil will cause high head pressure, the same way that a dirty outdoor coil will cause high head pressure in cooling mode. Be sure to also check filters and make sure that register grilles have not been closed off in certain rooms.
  3. Take pressure readings at all three ports on the outdoor unit. If this is a split system, the outdoor unit will have a third port that sits above the two service ports. This is called the true suction port. When measuring pressures in heating mode, the big pipe will show your discharge pressure, the little pipe will show your liquid pressure, and the true suction port will show your suction pressure back to the compressor. If there is a restriction at the indoor coil, or in the line sets, you may see a significant drop in pressure between the discharge and liquid lines.
  4. The last item on the list is charging. Charging a heat pump correctly is critical, especially when in heating mode. If you are forced to charge a system in heating mode, weigh the charge in per the manufacturers’ specifications. An over-charged system will cause efficiency problems and can cause component damage, but the most obvious sign of an over-charge in heating mode, is that it will trip on high head pressure.

Isolating a Furnace, Bypassing the Thermostat

Every day we receive many calls from frustrated technicians who are dealing with error codes on furnaces that, seemingly, can only be explained by a faulty control board. These codes may vary, but the consistent description is that the board is giving a code that “cannot exist”. One such example would be a pressure switch code when the pressure switch is clearly closed to the board.

One of the first tests that we will have technicians run is simply disconnecting all of the thermostat wires from the control board and jumping “R” to “W”. This may seem overly simple or elementary, but it is amazing the number of furnaces that are made to run correctly simply by removing the thermostat and thermostat wires from the system.

Keep in mind, the thermostat may be “functioning” properly; it may be calling for heating, cooling, or fan as commanded. But there are cases where the thermostat is found to be directly interfering with the boards’ performance. In these cases, the thermostats will need to be replaced.

We recommend that, if jumping “R” and “W” seems to allow the furnace to run correctly, you cycle the furnace multiple times before replacing the thermostat. This will ensure that the furnace itself is actually consistently working correctly.

Jeff Rosenblum
Technical Support
16 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

Testing a Single or Two Stage Gas Valve

Gas valves are an integral part of any furnace. They supply fuel to the burners, which enables ignition to take place. Gas valves have many integrated safeties in place to prevent dangerous failures. This can sometimes make them difficult to diagnose. Keep in mind that there are two key factors that need to be checked when diagnosing a valve.

  • Gas Pressure – Many technicians make the assumption that because the furnace has been running for many years, the gas pressure to the appliance must be sufficient. Both low and high inlet gas pressures can wreak havoc on a furnace. If the gas pressure is too low, the heat exchanger may soot up. If the pressure is too high (over 14iwc), the gas valve will lock out and will not open. Be sure to check the inlet gas pressure and adjust as necessary.
  • Voltage – Voltage to a single and two-stage gas valve should only be present with a call for heat. On most gas furnaces, this is a 24v signal from the ignition control. Some gas valves have resistance ratings through the coils, meaning that one can measure resistance through the two low voltage terminals (the coil of the valve) and find a potential failure. A good way to check for proper voltage/a failed valve coil is to connect the two low voltage wires from the gas valve to a 24v coil (such as a contactor coil) and attempt to fire the furnace. If the contactor pulls in, the ignition control is energizing correctly and has not failed.

The final thing to consider when dealing with gas valves is the “on” and “off” switch which is located on most valves. Be sure that this switch is turned “on” when attempting to light the furnace. Many technicians have wasted many hours and good gas valves due to overlooking this simple switch.

Jeff Rosenblum
Technical Support
16 Years Industry Experience
Cell (330) 962-2491
jrosenblum@famous-supply.com

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