Inital check-out and charging of Lennox system

[apowers]

First, I am a homeowner who has read a lot on this forum including the "For Your Interest" articles.

About a month ago, I had the following installed:

Lennox condensing unit (HSXA19-060) 5 ton, 2-stage scroll compressor
Lennox matching evaporator coil (CX34-50/60C) with factory installed TXV
Lennox 2-stage furnace (G60UHV-60C-110) (high blower fan speed at factory default of 1985 cfm).

I interviewed several companies and tried to choose a good company. I also checked the BBB and the company I chose had no complaints in the last 36 months.

I am concerned about how the intial charging and check-out of the system was done. I tried to choose quality equipment and want it to run as optimally as possible. I also can tell from reading the forum that there may be differing opinions on what is the best way to do it.

The company I used has a service tech come out after the installation crew finishes. When the technician came out, he put the unit in 2nd stage cooling by lowering the thermostat temperature to a very low value and letting the system run for several minutes, He put his pressure gauges on the condensing unit lines. He next used a thermometer to read the outdoor temperature about 2 feet away from the unit. He read 80 degrees F. He then looked at the table on the condensing unit panel. He showed me the following:

For Outdoor coil Entering Air Temp (degree F) 75 degree F ---- Liquid = 291 and Vapor = 135

For Outdoor coil Entering Air Temp (degree F) 85 degree F ---- Liquid = 334 and Vapor = 141

The table was labelel "Normal Operating Pressures - liquid plus/minus 10 and vapor plus/minus 5 psig" (also in the installation manual).

Before he put any R410A in, he told me that he read 310 for liquid and 120 for vapor. When he was done charging, he had 320 for liquid and 128 for vapor. I do not recall him taking any other temperatures as are sometimes described in your discussions for subcooling and superheat.

I also looked in the Lennox installation manual. It has a specific section for charging titled "Charging Using Normal Operating Pressures and the Approach Method Outdoor Temp greater than or equal to 65 degree F." This is the only section that talks about how to charge if the outdoor temperature is above 65 degree F. To summarize the section, it says to record the outdoor ambient temperature using a digital thermometer. Next to attach high pressure gauge set and operate unit to allow pressures to stablilize. To charge, use the same digital thermometer to check the liquid line temperature that was used to measure the ambient temperature. For the HSXA19-060 unit, the table in the manual shows that the difference between ambient and liquid should be 10.0 plus/minus 1 degree F.

I decided to do the Lennox approach method (with no pressure gauges) on 2 different afternoons with my Polder digital thermometer (outdoor temp about 97 - 99). The system was running on high stage for several minutes. I put the thermometer on the 3/8 inch liquid line about 2 inches after it comes out of the condensing unit and wrapped it with cloth first then with foam to try to prevent the outdoor air from affecting it. My delta T was only about 3-4 degrees F. I am the first to admit that I may not be doing this right or it may mean nothing.

Is the Lennox approach method what should be used? Am I doing the measurement correctly?

Did the technician do the charging correctly or should I ask for a technician to come back out? Is there a correct way to do an initial check-out and charging for my system? Thanks for your input.

[Shophound]

Is the Lennox approach method what should be used? Am I doing the measurement correctly?

Did the technician do the charging correctly or should I ask for a technician to come back out? Is there a correct way to do an initial check-out and charging for my system? Thanks for your input.

Without a gauge manifold attached to the system, the approach method cannot be done properly. The approach method is the difference between the saturated liquid refrigerant temperature in the condenser coils and the ambient air temperature passing over the coils. I suppose one could find the right spot in the return bends on the condenser coils to attach a type k thermocouple and get an approximate saturated condensing temperature, but it's far easier done with a gauge manifold and converting pressure to temperature.

Of course, only EPA certified persons can lawfully attach gauges to a sealed refrigeration system. Others do so at their own risk.

If your technician was competent enough to seek out Lennox's approach charging method and abide by it, chances are he was sharp enough to determine if your system was set up and performing properly.

Overall, the approach method works fine on Lennox equipment with clean coils, such as found on new systems such as yours. With older systems I'll check approach (after cleaning coils)against subcooling (TXV) and indoor delta T to ensure I'm seeing the performance the system should give.

[Irishmist]

I would agree with shophound. It would appear that this company and this individual are very consciencious if you only look at their procedure for the installation. They have techs that perform the physical installation and another tech that performs the start and check. Honestly I am impressed by their approach and procedures. It really sets a good example. Again, I agree, that the person in the best position to set the system up for optimum performance was the very person that did; the tech. He and his company are responsible for the operation and performance of the system, and sounds like they take a serious approach to it. There may be some that disagree, I would honestly be surprised, but I would definitely set up a regular service schedule (maintenance agreement) with this company. You obviously did not take the 'cheap' approach to your system, so you shouldn't scrimp on the maintenance. Sounds like they have earned the opportunity to provide you this. Hopefully lower utility bills and your overall comfort will serve to provide you with additional peace of mind. Although I don't put a LOT of confidence simply in BBB recommendations, I am glad to see you did your 'homework' and sounds like as a result, wound up with a quality contractor and a quality installation. Thanks for sharing. It helps to offset those stories we hear about techs that do diagnostics from the sidewalk.

[t527ed]

approach method measures liquid line exiting coil and outdoor air temp. if unit calls for 10deg +or-1 and you have 3 or 4 unit is overcharged. guages are not needed to check this.

[Shophound]

Originally posted by t527ed
approach method measures liquid line exiting coil and outdoor air temp. if unit calls for 10deg +or-1 and you have 3 or 4 unit is overcharged. guages are not needed to check this.

Yes, of course. I stand corrected.

[apowers]

So, since Lennox describes this charging technique (approach method) in its installation manual, should that be the one that is followed or are there other valid options?

[t527ed]

lennox unit, why any method but lennox's????

[tinknocker service tech]

lenox has a certain way they want the unit charged
if thier is a question on the unit and the rep has to come out he is going to check it this way also
all manufactors have thier methods and this is what we should follow. if you had 3/4 degrees on the approach then it is over charged. the pressure chart in the unit are for preseason maintence only not for original start up.
takes time to do the approach method properly and if the thamometer is not insulated from the out side temp you will never get it right. i have also found in some cases the farther away from the coil outlet the liquid line the cooler the temp seems to be sometimes 2 to 3 degrees
i test as close as posible
i would recomend if you are not sure about the tech ask them to recheck the charge. it may be right on and you are not checking it in the right place. be sides it is thier job to get it right. and dont worrie about what the presure chart says be cause it is refrence only and doesnt mean edged in stone

[cphc]

Most start up tech do a good job. You see I said most. It looks like this guy did a good start up. All that information in your owners manual is usually under idea conditions at the factory. Things are for real outside.
You install some very good equipment and you should get years of good service out of it. I would also recommend a service contract for your new equipment from the company that installed they seem reliable. Your manual should also warn you about the dangers of this equipment and to call a Tech. when repairs are required. R410a freon should not be played with.

Also in my years with equipment Reps. they want actual running numbers not what their book shows. Remember idea conditions.

[pipedope]

If the house is cooling i would say your probably fine. check the temp drop across the coil.

[t527ed]

lennox approach method is the easiest no brainer method i have seen for charging a unit. if the unit calls for 10deg differential between ambient and liquid temp that is what you make it.no this is the real world, no screwing around, no rules of thumb, no bull sh!t. temp to high add gas, temp to low take out gas.

[Milk man]

Seems when I check the subcooling after I have my approach temprature correct it is only two to three degrees. Kinda rubs what is taught wrong.

[apowers]

For the people who have used the "Approach Method", can an infrared thermometer be used, or is it better to use the digital thermometer with the stem and insulate the stem on the liquid line as best as possible to make sure the outdoor air temperature is not a factor?

[t527ed]

no infrared. use the digital.

[Wild Leg]

Originally posted by lynn rodenmayer
Seems when I check the subcooling after I have my approach temprature correct it is only two to three degrees. Kinda rubs what is taught wrong.

You were taught the same as I -- "old school".

Remember, the outdoor coil is called a condenser for a reason. It's primary job is condensing.

Subcooling, kept to a minimum, allows more room in the coil for condensing.

A classic symptom of an overcharged system is too much subcooling.

I would stay with Lennox's recommendation.

[ct2]

When is the use of an infared thermometer acceptable. I ate hearing that I wasted money on something I shouldnt be using

[Milk man]

Originally posted by ct2
When is the use of an infared thermometer acceptable. I ate hearing that I wasted money on something I shouldnt be using

It's a great tool for checking 2 by 2 drop in registers in 10' ceilings. You will come up with things to use it for. Just not good for copper pipe.

[dpatty]

Originally posted by ct2
When is the use of an infared thermometer acceptable. I ate hearing that I wasted money on something I shouldnt be using

I use mine for finding poorly insulated walls and ceilings. You can also use them on registers to see if you have poorly insulated ducts. Other than that I like playing with the laser.

Back to the subject at hand, call the company and explain to them what you are finding and they will almost certainly come out and recheck the system. You most like paid a fair amount for that system and your satisfaction will be important to them.

Just curious but was there any reason you didn't go with the XC21-060

[apowers]

I have contacted the company about my concerns and they are going to check it out. As far as the XC21-060, it is brand new this spring/summer. I know that it is supposed to be identical inside. It's the cabinet that has changed. There were 2 reasons. One, I am really reluctant to be one of the FIRST to get a new piece of equipment. I like to have others help get the bugs out. Two, the unit is about 3 1/2 to 4 inches bigger in depth and length. It would have fit in the same space but it would have been tight and I wanted to give the unit as much clearance as possible for air flow. I was only losing about 1 SEER by choosing the HSXA19 so I opted for the 19. The concept of the XC21 and the hinged panels seems like a great idea for cleaning.

[dpatty]

Good air flow is a very good reason to give up 1 seer in this range. I can also understand not being the first in line as well. Lennox is redesigning there equipment for ease of service and I think it's a wonderful idea.

Thanks for the reply.

[Edited by dpatty on 07-13-2005 at 06:40 PM]