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Eugene Silberstein

Eugene Silberstein

Joined on June 18, 2008

Last Post on June 28, 2014

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Checking PMRs and CMRs

@ June 28, 2014 9:05 AM in Current relay/potential relay

Checking a Current Magnetic Relay:

Take a resistance reading across the coil on the relay (usually terminals L and M) - The resistance of the coil should be less than 1 ohm or so.

Position the CMR in its normal position (coil at the bottom) and check for continuity across the contacts of the relay (Terminals S and L). This reading should be infinite. Now, with the meter's leads still connected to S and L, turn the relay upside down. You should now read continuity. This indicates that the contacts are moving freely within the relay.

If the coil and the contacts check out, the relay is good.

Checking a Potential Magnetic Relay:

Take a resistance reading across the coil (terminals 2 and 5) on the relay - The resistance of the coil should be very high. This resistance varies from manufacturer to manufacturer, but readings well above 1000 ohms are common.

Next, check for continuity across the contacts of the relay (Terminals 1 and 2). This reading should be zero or very close to zero.

If the coil and the contacts check out okay, there is still the possibility that the relay is not functioning properly. You still need to check whether or not the contacts open when the "pick-up" voltage is reached. The pick-up voltage is the voltage at which the contacts will open, and is much higher than the line voltage that is supplied to the unit.

I hope this helps!

Thanks for "weighing" in

@ June 27, 2014 6:19 PM in Freon leak

Not using a scale is not only unethical, it's also illegal.

Companies are required by law to keep detailed records regarding how much refrigerant is purchased, how much is sold, how much is recovered, how much is accidentally released to the atmosphere, etc. Guessing just doesn't cut it.

Yes, without using a scale, the equipment owner is most likely getting ripped off.

I heard of a technician (he actually used to work for us) who charged a customer for 40 pounds of refrigerant, when her PTAC unit only held 2 pounds!

When confronted, the tech responded to us, "When I got there the pressure was 30 psig and whenI left, the pressure was 70 psig. 70 - 30 = 40. What's the problem?"

Needless to say, the customer's bill was adjusted and the tech went on to pursue other endeavors.


0.43 psi/ft, not 43 psi/ft

@ June 26, 2014 3:52 PM in SubCooling

Rules of thumb, which you all know I hate, suggest using 0.50 psi/ft.

Having "NO LEAKS" is normal

@ June 26, 2014 3:50 PM in Freon leak

Ideally, system refrigerant should remain in the system and not leak out.... ever.

However, during the process of routine service, when technicians gauge up on equipment, for example, a small amount of refrigerant is lost. Although this may not be a big deal, over time, the losses can be significant enough to affect the system's ability to cool the space.

Now, do not think that the three pounds of refrigerant that was lost from the system happened overnight. It was very likely a gradual process that went unnoticed for many years.

Back in the day when folks like my father walked the earth, air conditioning men sized air conditioners so that, if the homeowner left the front door ajar or left a few windows open, the system would condition the entire neighborhood.

Having such an oversized system, the unit runs only a short time to satisfy the cooling needs of the space. As refrigerant leaks from the system, the ability of the system to cool the space diminishes, but the homeowner will never be able to tell the difference between a 10 minute unit run-time and an 11 minute unit run time.

As refrigerant leaks, the run cycles get longer and longer, until the unit runs continuously. At this point, the unit is matching the load on the structure. Now, as the refrigerant continues to leak, the system still runs all the time, but now the unit can no longer meet the cooling needs of the space.

Now, the homeowner calls for service and the system needs a few pounds of refrigerant.

So, to address your query. Most refrigerant, in my opinion, in a "sealed" system is lost during the processes of installing and removing gauges from a system.

On the other hand, there are things called "thermal leaks", which are leaks that are present when the pipes are hot, but "seal" when the pipes cool. These leaks are typically very small and extremely difficult to locate.

So, a loss of three pounds over 20 years is a beautiful thing and I think we would all sign up for that right now if we could.

I hope this helps.

Duct Help

@ June 9, 2014 12:22 PM in duct help

In a nutshell, you should definitely NOT use flex duct for what you are proposing. In addition to probably being a code/fire violation (depending on where you are) the resistance to airflow created by flex duct is very high. Using flex on both the supply and return ducts will very likely cause you have reduced airflow as well as nuisance high limit trips resulting from the overheating of the appliance.

Trane requires that duct installation be in accordance with NFPA 90.

What is the Superheat

@ June 8, 2014 8:42 AM in txv issue

The TXV has a "one-line" job description: To maintain constant evaporator superheat.

If the TXV is indeed maintaining constant superheat, the valve is operating. Let's take a look at an example:

You mentioned that the evaporator saturation temperature was 30 degrees (98 psig). Assuming that the superheat setting on the valve is 10 degrees, the temperature of the thermal bulb will be about 40 degrees, giving us about 118 psig inside the thermal bulb.

Now, you mentioned that you removed the bulb and let it hang and the evaporator saturation temperature rose to 42 degrees. If the valve is operating properly, the superheat will still be about 10 degrees, the temperature of the thermal bulb will be about 52 degrees, meaning that the pressure in the bulb will be about 148 psig.

Having not calculated the superheat, I would be inclined to say that the TXV is indeed operating since you, in essence, warmed the thermal bulb and the valve opened. With the bulb sensing an increase in suction line temperature (you removing the bulb from the line), the valve opened to allow more saturated refrigerant into the evaporator coil.

Also, I believe you mentioned that the high subcooling indicated an undercharge. High subcooling is an indication of an overcharge, not an undercharge.

Since you are experiencing an excess of refrigerant on the high side and what seems to be a deficiency of refrigerant on the low side, I would examine other liquid line components such as filter driers to see if there is a liquid line restriction, which is what I suspect.

Please keep us posted and let us know what you find.


@ June 3, 2014 6:58 AM in split system residential compressor overheating

Compressor overheating can be caused by a refrigerant undercharge. However, this overheating is not due to a lack of lubrication.

These compressors rely on the cool suction gas to cool the motor windings. If there is an undercharge, the superheat will be high and the temperature of the returning suction gas will be much warmer than desired.

Run Harvey Run!

@ June 1, 2014 8:52 PM in A little guidiance please?


Sounds like you need a Presto Magic Kit to go along with your refrigeration tools.

The function of the TXV is to maintain constant evaporator superheat so, adjusting the TXV will change the superheat but will not have a significant effect on the evaporator saturation temperature.

It seems like they should be incorporating Evaporator Pressure Regulators to maintain the evaporator pressures at the desired levels.

Hotch Potch can be good, but in the world of refrigeration, it usually does not end well.

Keep us posted and let us know what you find as you continue on your journey into the wonderful world of HP (hotch potch)


I would say...

@ May 27, 2014 5:08 PM in Nylog

I would say no, given that the product is oil. As with any product, protecting it from extreme temperatures would probably be wise, but I wouldn't do anything crazy like bring it in to my house at night and make certain it has a nice warm place to sleep after giving it warm milk and chocolate chop cookies... oh.... I digress!

Good product, but be careful.

@ May 27, 2014 12:32 PM in Nylog

Hey Harvey!

I have heard good things about the product from friends in the field, but have no first hand experience with it. If you use it, just be sure to select the right one. They make one for use with AB and mineral oil and one for use with POE oil.

I will say the following, though. If you have a leaking flare fitting due to improperly flared tubing, do not rely on this product, or any other sealant, to compensate for poor piping practices. If the flare is bad... REFLARE!

Also, many manufacturers use PVE oil, not POE oil in their equipment (Daikin, for instance). PVE and POE oils are not compatible with each other, so I would steer clear of using the POE NYLOG product on a system unless you have determined that the equipment does indeed contain POE oil.

I will be contacting the company to request some samples for use in the labs at the college and will update you in the future.

Enjoy your summer!

Sorry For the Delayed Response

@ May 7, 2014 6:30 PM in Happy Passover

Thanks Techman!

It was a great holiday. Things have been hectic and I apologize for not being around to harass you all.

I promise to become a pain in the butt again!


@ May 7, 2014 6:29 PM in Is R-410a a blend

Yes, R-410A is a blend, but a unique blend.

Typically, if a system that operates with a refrigerant blend develops a leak, the remaining refrigerant needs to be recovered and new refrigerant added to the system. In the case of R-410A, systems can be "topped off" due to the low temperature glide (0.3 degrees) of the refrigerant.

As a blend, R-410A is to leave the tank as a liquid.

Ventilation requirements

@ May 7, 2014 6:22 PM in HVAC Duct System

I do not have my copy of ASHRAE Standard 62 handy, but I am relatively confident that the second outdoor damper is to provide the extra outside air needed to satisfy the requirements for ventilation.

You mentioned that the space was previously a bank and is now a laundromat. This makes perfect sense since the ventilation rates are higher for a laundromat than for a bank.

These dampers are likely set to a minimum position to provide the required ventilation for the structure and one was likely not sufficient to meet the ventilation requirements.


@ May 7, 2014 6:10 PM in Mr Slim mini split ?

It is unlikely that the unit will short cycle to the point of sacrificing dehumidification. The "ON" cycles will likely be shorter than on a more precisely matched application, but the inverter-controlled compressor should take care of most of the issues with that.

Sounds Cool!

@ May 7, 2014 6:06 PM in Diakin VRV

I have not yet seen the VIV but am looking forward to it. I heard about the features but have also heard that it is not a very pretty thing to look at. I am also hearing that there will be shipping/damage issues since the packaging on the equipment is sparse at best.

We have a VIII system installed in our controls lab at the college that has 6 indoor units.

I love the technology and am interested in seeing the filter vacuum in action.

System MisMatch

@ May 7, 2014 6:02 PM in 2.5 Condensor with a 5 ton coil

You will provide some degree of cooling to the space but, as Techman mentioned, your low side pressure will be high and this will cause the temperature of the evaporator coil to rise as well. This may sacrifice the coil's ability to dehumidify the space. If such is the case, be prepared to deal with a cool, clammy space... Not very comfortable.

Reducing the blower speed will help alleviate this problem, but evaporator coil freeze-up may very well become a problem.

I would personally steer clear and have the correctly sized equipment installed.

Delta T

@ May 7, 2014 5:57 PM in figuring CFM required

The Delta T value is the temperature rise across the appliance. With the furnace running, you take temperature readings of the return air coming into the appliance and the temperature of the supply/heated air coming from the appliance. The difference between the two is your delta T.

Now, if the area to be conditioned is far from the furnace, or the ductwork is not adequately insulated, the cfm value may very well need to be increased to take the duct losses into consideration.

You also have to have reliable numbers with regards to the actual heat loss of the room, so be sure that you are using a Manual J, or similar, method to determine the needs of the conditioned space.

Be Aware of Nested Coils

@ April 14, 2014 6:36 AM in AC cleaning condensor coils - inner side seems dirty

Some manufacturers are using nested condenser coils, that actually look like one coil nested inside the other. In instances where the condenser is very dirty, the condenser will need to be carefully lifted and removed from the condensing unit housing and separated to access the space between the sections. Dirt can accumulate there and can be extremely difficult to get out.

As with foam cleaners, be patient. Spray coil, spray cleaner, WAIT, wait a little longer, gently spray to remove foam cleaner.

If you spray water through the coil immediately, you are not giving the cleaner a chance to, well, clean.

Don't rush coil cleaning. Take your time, do it right.

Enjoy the warm weather!

I'm with Techman

@ April 11, 2014 10:31 AM in Filter Dryers and moisture indicators.

As long as the pressure rating is okay, then I say, "GO FOR IT!"

Glad to Hear

@ April 6, 2014 9:31 PM in Freon leak vs. moisture

Al is a good man.

I'm just glad that we were able to clear this up. I'm all about getting accurate information out to my peeps!

The Verdict is in!

@ March 27, 2014 2:13 PM in Freon leak vs. moisture

I spoke with two of my colleagues from the physics department here at the college, and the answer is.....
Moisture cannot enter the system if the presure in the system is higher than the pressure outside of the system.
We must look at the total pressure in each area (inside the system and outside the system) to determine the direction of fluid flow. Fluid flow refers to liquids and gasses. Even though the "water vapor pressure" is higher outside the system than inside the system, given the absence of water vapor inside the system, the total pressure in the system prevents water vapor from entering.
This will hold true unless the pressure inside the system drops to atmospheric, at which point, "all bets are off".
Thanks to Professors Janet Haff and Muhammed Khalik for confirming!


Glad You Like It!

@ March 27, 2014 1:27 PM in Coffee tastes better in a "THE HVAC PROF" mug!

Glad you like it!
Anything to help you get your caffeine fix!
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