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

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

Why Use a Start Assist Device On Your Compressor

Many times we receive questions as to why someone would want to install a start capacitor (5-2-1). There are several reasons why this would be beneficial. As a compressor ages it may become more di cult to start. The windings may be ne, and once it’s running it operates properly, however, sometimes it just doesn’t want to get going. Oftentimes, adding a start assist device can give the compressor a bit of a boost.

This same theory applies to new units where the compressor may have a di cult time starting. Many times technicians think the compressor needs replaced, so why would a new unit need a start cap? Oftentimes, with long line sets or TXV’s, a start cap is recommended, and newer compressors are built with closer tolerances. As we try to manufacture units with more efficiency and less chance of bypass gas (which robs efficiency) we end up making the compressor tighter. Just because a new compressor doesn’t start, doesn’t mean it’s bad. Sometimes a little boost is all it needs. Just like us, we need co ee to get us going, a compressor needs a start assist to “wake up”.

Some of the benefits of a start assist are less wear and tear on capacitors, less light dimming on startup, and reducing the chance of a breaker tripping on start up. Before you condemn a compressor, try a Start assist (5-2-1).

I was told back in the day that start assists are only for failing units. This is not true. They can be used on new and existing units without problem. I have used them successfully for years. So before you say a seized compressor must be replaced, try a 5-2-1. You may be surprised by the results.

Jeff Rosenblum
Technical Support
17 Years Industry Experience
Cell (330) 962-2491

Sizing Equipment

We often get asked, “What size furnace/AC do I need?” The answer is not as simple as just knowing the square footage. There is a lot that goes into figuring out the right size.

So, what information is needed to figure out the right size? First, we recommend you use the Manual J sizing program. Second, you will need to know some key points.

  • House/building square footage      •  People load
  • Number and size of windows          • Additional load (lights, computers etc.)
  • Outside exposures 
                            • Unconditioned Spaces
  • Amount of insulation throughout the house • Weather info for the area
  • Number and type of doors 
              • Solar Gain
  • Amount of infiltration air 

               • Ventilation
  • Which way the house faces 
             • Humidity

This may seem like a lot of info in order to size equipment, but figuring out the design load is very important. If the system is too large, it can have a very short run time, may not humidify or de-humidify correctly, and the system will be inefficient. If it is too small, it may never satisfy the load of the building, which leads to being uncomfortable, and it is also inefficient. Either way will reduce the life of the equipment. Guessing the size is never the answer. Size the system the right way and keep your customers comfortable and happy!

Jeff Rosenblum
Technical Support
17 Years Industry Experience
Cell (330) 962-2491

Choosing the Proper Mitsubishi Electric System

I have received several questions regarding which Mitsubishi system would be appropriate for their application. Since Mitsubishi systems can t in a wide range of applications, selecting the right one can sometimes be a daunting task. There are a few key things to consider when selecting the right system.

Where is this unit going to be used? If it is in a commercial system, we recommend using the P series system. This system gives you the ability to link up to 16 systems to a common control. The P series is also the unit to use for non-critical server rooms because of its low ambient cooling capability. If it is a residential home/sunroom/ addition, an M series may be the better choice.

What size system do you need? A load calculation must be done in order to decide which size is best.

Is this going to be a multi zone system? Look around and see if there are other areas that can be covered. Usually, a simple question to the homeowner of “are there any other areas of concern?” will point you in the right direction.

Unit location is a key thing to look at. Where is the indoor unit going to be mounted? Will you need a condensate pump? How long is the line set going to be? Where will the outdoor unit sit? We must nd out where everything will be located to avoid potential setbacks.

Do you have enough power for the system? A quick look at the main breaker panel will tell you.

These are just a few of the things to pay attention to when considering a Mitsubishi system. Once you have all the necessary questions answered, then you can have a better idea of what system will be best for your application. If you need assistance in selecting the right Mitsubishi system please feel free to call the Famous Supply tech department at 330-962-2491

Jeff Rosenblum
Technical Support
17 Years Industry Experience
Cell (330) 962-2491

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

Diagnosing a Smart Valve, First Generation

First generation smart valves act as ignition controls and gas valves. There are internal and external safeties that can prevent the valve from working properly. As the valve operates on a 24V signal from a blower control or thermostat, diagnosing these valves is relatively simple.

The smart valve 1 has a 4 pin Molex plug that attaches to the top or side of the control. This 4 pin plug houses 4 wires: a 24V hot, 24V common, electronic fan timer output, and a 24V input from the pressure switch (see diagram below). You should find 24V present between the 24V hot and common at all times when power is applied to the furnace. With a call for heat, the blower control will energize the induced draft blower, which will close the pressure switch. When the normally open pressure switch closes, 24V will be introduced to the pressure switch wire at the valve. This allows the furnace to attempt to light the pilot. After ignition has occurred, the valve will send a 24V signal back out on the EFT terminal to energize the blower motor.

If the pilot light will not light, verify voltage to the pressure switch terminal and the 24V hot terminal. Check for voltage to the igniter with the igniter plug still attached to the valve. If the pilot will light but not the main burners, check flame sense to the valve. Verify that the pilot tubing is securely attached
to the valve.

Jeff Rosenblum
Technical Support
16 Years Industry Experience
Cell (330) 962-2491

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

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, 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.

Proper Start Up

The summer is in full swing and I’m sure you are staying busy. With that being said, please take time to do a proper start up on that brand new AC unit you just installed. As I have said many times, we don’t live in the age of just hooking up an AC and letting it run. Things have changed! We must pay special attention to the process we use to install and start that new equipment.

When doing the initial install, you need to flow nitrogen through the line set as you braze to prevent oxidation on the inside of the lines. Then when pulling a vacuum, use a micron gauge to make sure you have reached the correct level of dehydration. Now that the system is installed, the job is not done yet. Make a point to check and adjust the cooling speed for the correct CFM per ton. Typically use 400CFM/ Ton. The static pressure should also be verified to ensure that the ductwork is delivering enough air to the conditioned space. Then and only then connect the gauges to verify the refrigerant charge.

By following these steps, you can feel comfortable that the system will perform as expected and deliver the comfort your customers expect. By installing a system that makes your customers not just happy, but ecstatic, you will have a much better chance of that customer giving you rave reviews to prospective buyers.

If you need any assistance in the start up process, please call the Famous Supply HVAC Tech Support Team at 330-434-5194

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