Selecting an Air Conditioning & Heating Contractor - Air Conditioning and Heating Efficiency Check Up 

Selecting a Competent Air Conditioning and Heating Contractor - Determine the Metering Device TXV or Fixed Orifice without Looking
There are numerous things you can do to reduce heating and cooling costs!
* Customers A Simple Check byou can do!

with Darrell Udelhoven - HVAC RETIRED - udarrell

"Within your particular area, select a Contractor who has the expertise to enable you to achieve optimal comfort, efficiency, and savings with your Heating and Air Conditioning system.

"A lot of AC systems, older furnace air handlers and duct systems, are not delivering anywhere near the AC Unit's BTUH and SEER Ratings. This is primarily due to inadequate cubic feet per minute (cfm) of airflow through the evaporator coil, and/or dirty fins/coils and blower wheels.

Additionally, even more common in northern areas of the USA, is the result of supply discharge air and return intake air being at the floor level where all the coldest air is merely being recycled through the evaporator coil. It is near impossible to fully heat load an air conditioning evaporator when the air flow is recycling too much of the cold supply air from the floor level. For air conditioning, the supply air outlets and air returns should be at, or near, the 8-foot ceiling level.

The later model furnaces with bigger horsepower blower motors and blower wheels can result in too much airflow through the cooling coil, the result is that some incompetent, so-called, technicians end-up overcharging the system, trying to get a beer can cold suction line. The result is greatly reduced btuh system capacity and a deadly drop in the paid for SEER level!

Adjusting the furnace for maximum efficiency: This cannot be done by visual inspection alone; it requires four different measurements made through a pencil-sized hole in the flue pipe, close to the furnace. Flue gases will not escape through the hole.

After the furnace has been running for about 15 minutes to a steady flue temperature, a sample of the flue gases is tested for its smoke content and the draft pressure is checked. The final two measurements are then taken to determine the steady-state efficiency of the furnace: these are the temperature and the carbon dioxide or oxygen content of the flue gases leaving the furnace.

All four tests are necessary to properly adjust an oil furnace for optimal performance.

You can tell whether your furnace has ever been tested by looking for a pencil-sized hole in the flue pipe. If there is no hole, then the smoke level and draft pressure have never been tested, and the steady-state efficiency has never been checked. If this is the case, talk to your fuel oil supplier or service person about it.

*Cleaning the interior channel surface areas of oil furnace heat exchanger. Use heat exchanger brushes and a shop vac with a ten foot one inch diameter hose to remove soot buildup from Thermo Pride OL11 heat exchanger cavities. These are difficult to reach in many oil furnaces. This is critical to efficient performance and safe burner operation!

It will pay you to find an A/C tech that knows his field from A to Z.
Determining which metering device the system has without physically looking

If you do not absolutely know whether the metering device is a TXV, or a fixed orifice device or cap tube. 

Hook up your manifold gauges, block off considerable condenser air intake for a short time.
If the suction pressure starts rising, you have a piston, or a cap tube.
If only the high side goes up, you have a TXV.

Have things with you in your van or truck to block-off the condenser air for a short time.
Check every time you are not certain what metering device it has.
There will be a lot of guessing in the future.

Do this procedure on known metering devices to observe the difference.
Report back to me how well it works for you.

In some situations, that could save you from cutting a hole in the plenum.

Squirrel cage wheels with forward curved blades on residential systems
unload when discharge air is blocked off too much & will overload
when there is no static pressure.
There is a preferable ESP range for each Air Handler blower design, that ought to be listed on the blower; they vary at the point of serious unloading.
 If you amp-probe check enough of those blower motors, if the amp draw is too low according to its rating, you can begin to tell that the External Static Pressures (ESP) is too high.
Additionally, mfg'ers could list the amp draw at various design ESP numbers, then we could amp-probe & know if it was too far above the amp rating, a duct maybe off,
if amp reading is too low, it is time to check all static pressures & delivered CFM to each room.

I lot of us used to set a nearly empty R-22 cylinder on top of a condenser to warm it a little. Back then fan motors had more HP
& higher amp draws, therefore it didn't seem to cause any harm, just more noise.

Back in the 1960's & 1970's there were a far number of TXV metering devices & some table top condensers' that had the fan underneath blowing up through the coils.
Well, where there were cottonwood trees, nearby clothes dryer lint vents, or a lot of leaves or other debris under the unit, the fan motors would be blocked overload & burnout.

I don't understand the engineering genius of that moronic design.

However, on hot days & a heat-loaded E-Coil,
You could move your wrist over the condenser from outlet up to inlet, & tell if the liquid was taking up too much area of the coils; an overcharged system. - udarrell
Always get the CFM airflow correct, first, if it is a piston or cap tube, use the superheat method to charge it.
If it is a TXV, subcooling is the way to charge it, but check the Superheat to verify the TXV is holding within its known specs

Darrell Udelhoven

Any of the HVAC companies I list on any of my web pages have nothing to do with the information I post on any of my Web pages nor do I assume any responsibility for how anyone uses that information.
All HVAC/R work should always be done by a licensed Contractor! This information is only placed on these pages for your understanding & communication with contractors & techs.

This information is for the edification of contractors and techs. I am NOT liable for your screw-ups, you are liable for what you do! - Darrell Udelhoven

Darrell's Refrigeration Heating and Air Conditioning - Federal Refrigerant Licensed - Retired Licensed Contractor from another state.

"Getting it done RIGHT, makes all the difference in the world."
Grant County, Iowa County, Lafayette County, Wisconsin;
Crawford County, Wisconsin; Fennimore, Wisconsin
Beetown, Cassville, Potosi, Dickeyville, Lancaster, Wisconsin

Contractor Servicing Oil Furnace's Sooted Heat Exchangers

"Getting it RIGHT, makes all the difference in the world."

Please write me if you have anything you'd like to contribute! - Darrell 

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Posted: 01/09/04; Updated: 07/28/08