Joined on June 18, 2008
Last Post on December 4, 2013
@ December 4, 2013 10:03 PM in help with measuring airflowSorry, but I just stumbled onto this post.
The equation being used is incorrect, which is why your numbers are causing you grief.
The formula for airflow is:
CFM = Air Velocity (ft/min) x Cross sectional area of the duct
The velocity of the air is given by 4005 multiplied by the square root of the velocity pressure, not the square of the velocity pressure.
So, your numbers will look something like this:
CFM = 4005 x Square root of 0.2 x 3.14 x 2"/144
where the 2" is the radius of the duct and the 144 is the conversion between square inches and square feet.
CFM = 4005 x 0.14 x 3.14 x 2/144
CFM = 49.2
Hope this helps
@ December 4, 2013 7:46 PM in Start cap ,start winding ; run cap ,run windingI bet you were thinking about this all day!
@ December 4, 2013 6:21 PM in Ask Yourself "Why"?In class, I always tell my students to ask themselves why something has happened in order to trace the system back to the initial cause for system failure. Here's a quick example:
You go on an air conditioning service call and the customer is complaining that the system is not cooling the house. You gauge up on the system and determine that the compressor is operating, but the high and low sides pressures are the same. You check the compressor and determine that the valves on the compressor (yes, it's a recip) are leaking. You replace the compressor... Lo and behold, a few weeks later you are back on the job replacing the compressor again... Hmmm... Here's how things could have gone a little better.
You gauge up on the system and determine that the compressor is operating, but the high and low sides pressures are the same. You check the compressor and determine that the valves on the compressor are leaking. Why are the compressor valves leaking? Probably because liquid refrigerant has gotten into the compressor. Why has liquid refrigerant has gotten into the compressor? Because there was liquid in the suction line. Why is there liquid refrigerant in the suction line? Because the evaporator is being overfed. Why is the evaporator being overfed? Because the TXV is fully open. Why is the TXV is fully open? Because the thermal bulb is hanging freely in the return air stream. Why is the thermal bulb hanging in the return airstream? Very likely because the guy who was there had no clue about what is to be done with the thermal bulb on the TXV.
Yes, you will still need to replace the compressor, but in addition to the compressor replacement, you will also have to resecure the thermal bulb.
So, why am I mentioning this to you all? I was down in Orlando Florida for Thanksgiving and stayed at my sister-in-law's house. She asked if I could replace the toilet in her master suite as the water continues to run and keeps her up at night. I told her that the parts in the tank could easily be replaced and that there was no need to replace the entire toilet. She told me that all of the parts in tank have already been replaced twice by two different plumbers and that the problem still persists and she wants the toilet replaced. No problem.
I look at the toilet and notice that the float assembly in the tank is brand new, but the flapper assembly looked like Noah had it on the ark with him. She showed me the paperwork from the two plumbers and they both replaced the float assembly. Wow!
The complaint wast that the water was continuously running so they replaced the float... TWICE!
I was astonished that they simply did not ask themselves why the water was running. How about.... the water is running because water level in the tank is going down. Why is the water level in the tank going down? Because water is leaking out of the tank. Why is water leaking out of the tank? Because the flapper is not making proper seal at the bottom of the tank.
The poor float was just trying to maintain the correct water level in the tank.
So, $12 later the water has stopped flowing and my sister-in-law can sleep!
Hope you all had a great Thanksgiving!
@ December 3, 2013 4:24 PM in I am so sorry for not answering my emailsGlad to hear you are on the mend.
@ November 21, 2013 4:39 PM in screw terminal quick disconnect adapterGrainger part number is 6X578.
@ November 21, 2013 4:34 PM in Nitrogen pressureIf the temperature dropped 30 degrees, you should have a pressure drop of no more than 24 psig 0.8 (80 - 50) = 24 psig. You mentioned that you lost 3 psig.
I would call that a homerun.
@ November 19, 2013 4:30 PM in Nitrogen pressureMany people call nitrogen "dry" if it is not liquid. However, the term "dry" refers to the moisture content in the nitrogen. Industrial nitrogen, which is what most air conditioning guys use for system pressure testing, can have moisture contents over 400 ppm.
What we should be using is medical grade, NF, nitrogen, which can have moisture contents lower than 10 ppm. Of course, NF nitrogen is much more expensive than industrial nitrogen, but it will hep reduce evacuation times as well as contribute to extended equipment life expectancy.
@ November 17, 2013 10:18 PM in Help with Daikin split unit (basic operation seems inefficient)I'm surprised that you are having problems finding literature. You might have gone to the corporate website, but you want to be at the North American site.
Daikin is one of the few manufacturers that makes all of their literature available to everyone!
Simply visit their website:
You can access all of the installation and operation manuals for their entire product line. No secret handshakes, no passwords.
@ November 17, 2013 10:11 PM in Nitrogen pressureThere can indeed be a pressure difference between the time you pressurize the system and the time you check the pressure. There is a neat little formula that will give you the acceptable pressure loss on a system. The formula is:
0.8 (Tp - Tc) = Pressure Loss
Where Tp is the ambient temperature when the system was pressurized and
Tc is the ambient temperature when the system pressure is checked.
For example, a system is pressurized to 200 psig when the ambient temperature is 100 Degrees and the system is checked the next day, when the ambient temperature is 80 Degrees, and the pressure in the system is 160 psig.
The acceptable pressure loss is 0.8 (100 - 80) = 16 psig, so the system pressure should be 200 - 16 = 184 psig. The system pressure of 160 psig indicates that there is a leak in the system, as the pressure is too low.
As an aside, we have to be careful that we use "dry" nitrogen to pressurize our systems. The nitrogen we get from welding supply houses is NOT DRY. Be careful!
@ November 9, 2013 7:46 AM in Ah GeezeYou couldn't help it make it to an even 30?
Great job.... as usual!
@ November 8, 2013 11:02 PM in reversing valve change out on a heat pumpJust don't put the old reversing valve under your pillow. The reversing valve fairy is not paying as much as the scrap metal dealer!
@ November 8, 2013 10:05 AM in reversing valve change out on a heat pumpAs David mentioned, changing a reversing valve is a time-consuming tedious process. There are a couple of other items that should be mentioned.
Do not throw away the paperwork that comes with the new reversing valve. Not all manufacturers "etch" the piping configuration on the valve body. It is important to know what ports are connected to what ports when the valve's coil is energized or not. Failure to properly connect the indoor and outdoor coil ports on the valve will cause the system to operate in the wrong mode.
Be aware of the mode of operation in which the system fails. Most, but not all, heat pump manufacturers design their systems to fail in the heating mode. This is because, in most areas, heating is far more important than cooling. When failing in the heating mode, the system will provide heat if the reversing valve or holding coil fails.
Finally, if you are replacing the reversing valve on a system, it is best practice to replace the coil as well, especially if the replacement valve is manufactured by a different company. Even if the old coil "fits", there is the very real possibility that gaps between the coil and the valve can cause overheating and improper valve operation.
@ September 29, 2013 8:46 PM in head pressure control - split systemYou seem to be addressing two issues here. One is the use of some type of fan control and the other is referencing oil return concerns.
Head pressure controls are always desirable as they have the ability, depending on the number of fans and the strategy employed, to maintain the head pressure of the system within a desired range. This can be done by altering the speed of the fans, by cycling them on and off, by controlling the amount of refrigerant that is able to bypass the condenser coil altogether or by controlling the amount of air available for the fans to move (shutters and dampers).
Oil return is a completely different animal. Adequate oil return can be achieved by ensuring that best field practices were observed when the system was installed.
For example, if the air handler is below the condensing unit, there should be a trap in the suction line at the base of the vertical run up to the condensing unit. In addition to this trap, there should be an additional trap for each 15 feet (or so) of vertical rise to the condensing unit. There should also be an inverted trap at the very top of the suction line run and the suction line should slope downward to the condensing unit to ensure proper oil return. Assuming that these guidelines have been followed, oil return should not be a concern.
@ September 29, 2013 8:36 PM in Pneumatic controlsTerry,
Are you asking about pneumatic controls that are used on VAV boxes in common areas (hallways, etc) in apartment buildings? If so, what's on your mind?
@ July 12, 2013 10:38 AM in Technician InjuredA local air conditioning/heating technician was injured on a job on Tuesday while he was replacing a compressor. He attempted to unbraze the discharge line on the compressor. The oil vapor, mixing with the ambient air at the time the line was freed, ignited and, in essence, turned the compressor into a blow torch.
He is presently in the burn unit at a Manhattan hospital with severe burns and is facing a long, painful recovery.
Gentlemen, please keep in mind that your FIRST access to an air conditioning system should be with a tubing cutter, NOT a torch.
Let's pass the word and stay safe!
@ July 12, 2013 10:32 AM in condensationIt is best practice to insulate the condensate drain line for a minimum of ten feet to help eliminate the condensation issues.
@ June 7, 2013 2:00 PM in High subcoolAs Techman asked earlier, what are the 67.8* and 63.8* temperatures?
As far as noncondensables go, they will cause high subcooling but they will also cause the high side pressure to rise. With an outside ambient temperature of 75* and a condenser saturation temperature of only 91*, this does not seem likely.
What was your return air temperature and what was your evaporator superheat? Even though you have a TXV on the system, knowing what the valve is doing is helpful.
Also, as far as a sight glass always being full on a TXV system, such is not the case. If the load on the system is very high, the TXV will open wide to attempt to bring the superheat down. When operating like this, it is possible for refrigerant to flash in the liquid line, causing bubbles to form. I think what Techman is saying is that if the system is operating close to its design temperature, then yes, the sight glass will be clear on a TXV system.
One word about suction line filter driers. They can, and often are, installed on systems unless the manufacturer specifically states otherwise. Daikin, for example, stresses in their literature that filter driers of any kind are not to be installed on their equipment. There is nothing wrong with installing both suction and liquid line driers on new systems AS LONG AS THEY ARE PROPERLY SIZED so as not to adversely affect the mass flow rate of refrigerant through the devices.
Keep us posted with your findings on this system.
Enjoy the Summer!
@ June 5, 2013 10:02 AM in New HomeOwner with Central A/C - Is this condition normal?Although the most obvious possibility is a system undercharge, there are other potential problems with the system. These include liquid line restrictions and deficiencies in the return air stream.
If there is a liquid line restriction, or underfed evaporator, the cooling coil will not be fed enough refrigerant and the system will not provide adequate cooling. The operating pressures will be low and the evaporator superheat will be high.
If there is a damaged return duct, which could be the result of improper duct sealing or someone stepping on it, some of the air in the attic will get pulled into the return duct along with the air from the occupied space. This increase the temperature of the air that the cooling coil sees. In this case, the coil will cool the air down, but not to the point that the house will be cool. Here's an example. If the house is 80 degrees and the temperature of the air in the attic is 120 degrees, a damaged return duct can cause this warner air to mix with the air in the space, resulting in, let's say, a 90 degree return air stream at the air handler. If the cooling coil pulls 20 degrees off the air, the supply air will be in the 70 degree range. This 70 degree air will not be sufficient to cool the space.
So, the bottom line is, have your service company come out, check the system and determine where the problem lies with your system.
Please keep us posted.
@ May 17, 2013 6:12 PM in r22 condenserSince you did not do the original changeout, you cannot be certain that the system was properly evacuated.
If your static pressure is only 30 psig and you are getting extremely high pressures when the system is turned on, it is very likely that there is either air or nitrogen in the system. If the pressure rises immediately, I am leaning towards nitrogen. There is also the possibility that there is a mixture of refrigerants in the system.
In either case, recover the refrigerant (being very careful to not overload the compressor in the recovery unit), pull your 500 micron vacuum and recharge.
I mention being careful with the compressor in the recovery unit simply because, if there are noncondensables in the system, your recovery unit compressor will overheat. Throttle the refrigerant into the recovery unit SLOWLY with the low side valve on your gauge manifold and TAKE YOUR TIME.
Hope this helps.
@ May 17, 2013 1:04 PM in Professor Silberstein is a MAMMA's BOY!Glad to be one!
Hard to believe, but February 7 marked the 7th anniversary of my mom's passing.
Time marches on, but fond memories live on forever!
@ May 17, 2013 1:02 PM in A hug ,a handshake and some tears.I'm referring to both of you!
Francisco is indeed a good man, but he is a better man because of, in part, the experiences he had with you.
He was well-trained on all fronts and we all wish him the best with Trane.
I'm hoping your future hires from the college will do us proud as well.