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Joined on April 16, 2013

Last Post on March 25, 2014

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@ June 14, 2013 12:32 PM in High subcool

Lets look at #1 first. You listed your static at 180, which means your condenser is 9 degrees colder than ambient. This should not be the case! I'm going to guess that since your RAs are in the 50's, you are stacking liquid in the condenser because you have no load. That also makes sense as your SH is not that far out of line, if at all. Three things still bother me; why is there an SLD, why is it not next to the compressor where it belongs if it is really needed, and the PD is too high. Disregarding the SLD for the moment, I would crank on the furnace to raise the indoor temperature to the 80's. Even though it would be all sensible load, at least you would see if your SC comes up. If it doesn't, checking for an overcharge may be the next logical step. All of this is assuming your air flow is correct, of course.


@ June 12, 2013 3:44 PM in Sight glass again

I am just as much against overcharging as undercharging; hence, my reliance on manufacturer's prescribed methods and nomos in the unit. Overcharging does not create saturation. Overcharging creates overcharging. Saturated refrigerant is what you see on your manifold gauges. In its purest form, saturated means adding heat changes liquid to vapor; taking away heat changes vapor to liquid. That is why the actual liquid line temperature must always be colder than its saturated temperature, which you see as pressure on your manifold and then convert to temperature. A classic example of this is Ingersol Rand; after the last circuit through the condenser coil, you will find an extra pass of tubing upstream of the LLD and service valve. This is a "sub cooling loop." The thought process is that if the refrigerant is allowed to stay in the ambient just a little longer, then the extra time is assurance that as much superheated vapor has been condensed as possible and feeding the TXV with only liquid. That overcharge has to go somewhere, so it will stack in the condenser. Since the condenser must be exactly that, and not a receiver, then the resultant capacity loss from the OD coil not being allowed to do its job is a risk not worth taking.

SG Again

@ June 12, 2013 2:38 PM in Sight glass again

If my charge is correct, and my sub cooling is correct, how could the refrigerant in the liquid line possibly be saturated? It was 7 degrees below that point; the range where the factory wanted us to be. 100% liquid into the TXV. That's what sub cooling is!

SG Again

@ June 12, 2013 9:26 AM in Sight glass again

I can't speak regarding low-temp, but for residential DX cooling, I know of no maker who supports charging to a clear sight glass.

In an experiment with an HVAC tech school, we had an R-410A machine stamped 9 pounds one ounce of factory charge. Since the manual told us that was for the OD unit and a 15' lineset, we installed a 15' lineset and the AHRI smallest rated coil. The conditions at the time required 8 degrees of sub cooling (+/- 3 degrees). We had 7, so we were happy with that. We then removed the refrigerant, installed a sight glass, and added refrigerant until the glass was clear. Removal of the refrigerant this time revealed ten pounds three ounces. Proof enough.


@ June 11, 2013 11:15 AM in Heat loss Calc, correct wi ndow measurments

Correct! Then, once you have your type and size, take into account blinds, shading, awnings, orientation, and whether or not the glazing is flat against the wall (as opposed to a bay, bow, skylight, or garden window) and you're in pretty good shape. If you're wondering about the different grades of windows, glazing insulation value is shown in a "u" factor. "R" and "u" are a reciprocal; 1/R = u, and 1/u = R. For example: if your window has a u-factor of .36, then insulating value is equal to R-2.8.


@ June 10, 2013 4:15 PM in High subcool

Something is amiss here. Your static test should not indicate your condensing temperature is 10 degrees COLDER than your ambient, and with an abnormally high SH, it is impossible your condensing temperature would be colder than ambient. Unless you have a heat pump operating in heating mode, of course. Also, your PD across the SLD is too much.

Window Measuring

@ June 10, 2013 9:11 AM in Heat loss Calc, correct wi ndow measurments

When you are working with load calculations with respect to windows, you are working with "fenestration." It is a term used to describe all types of glass (windows, doors, skylights, etc.). The term applies to the entire assembly of glazing, sash, and framework that fits into a rough opening.


@ June 9, 2013 9:40 AM in High subcool

Too cool! There are two things I really dislike; losing my car keys and losing compressors. And, I'm sure you will agree that after what we see in the field, someone lost their car keys in the compressor.

I've really enjoyed being on "The Wall." With the security check, my math is getting better. Sometimes, I don't even use a calculator.


@ June 9, 2013 7:55 AM in High subcool

If you are using this device for ONLY checking moisture or oil condition, then I'm with you. However, I remain a proponent of the static test for non-condensables for one small issue and one huge issue. The small issue is two extra potential leak sources. The huge issue is with a static test, there is no way anyone before or behind you can use it a a charging method.

For rickh

@ June 7, 2013 5:03 PM in High subcool

Your step-by-step plan of attack, in #5, states: "pressure test to 400." I like your plan, yet personally I would use factory test pressure. It might be 400 PSIG; it might not be. After all of this, I would hate to see you create your own leak.

High SC

@ June 7, 2013 4:52 PM in High subcool

OK, I'm with you. But what does it matter what is in there? It has to come out anyway, so who cares if its water, nitro, or Jack Daniels? If the removal process is done correctly, you get it all, or at least enough to get the percentage of nasties to a tolerable level. With R-410A for example, we will probably never get all of the moisture out, yet a well-done evacuation and an oversized LLD at least gives us the satisfaction of doing the best we can with what we have.

Static Pressure

@ June 7, 2013 4:25 PM in High subcool

I humbly and respectfully disagree with your statement. Your head pressure converted to temperature and the ambient must be equal. A change of more than 3 degrees indicates non-condensables (provided you have checked for a restricted condenser). Head pressure converted to temperature most certainly involves a refrigerant gauge and a PT chart, having no correlation to water pressure. What it is, be it moisture, nitrogen, etc. matters not. It has to come out.


@ June 7, 2013 1:46 PM in High subcool

Your static test will show if you have moisture.

SC Issue

@ June 7, 2013 10:13 AM in High subcool

If no burn-out, get that SLD out of there fast, as well as that sight glass. If you DID have a BO (better find out before going any farther), the SLD should hug the compressor. You should probably retest the compressor (again, only if a BO) for acid and sludge. I hope somebody didn't scab in a LLD on the low side! ANYTIME you open a system to atmosphere you have to change the LLD; get the biggest one you can. While the system is open you may as well make sure the TXV inlet screen is not plugged. If your manufacturer says it is OK, an Rx11 with nitro purge wouldn't hurt either. Also, make sure your manufacturer is happy with a 10' lineset. The factory charge is for 15' so too short may be trouble unless you add some more tubing.

The first thing that comes to mind with the SG is an overcharge, especially with your tubing so short. Lets hope for no BO, so you're down to getting rid of that SLD and sight glass, removing the LLD and installing an oversized one, checking with your unit's maker regarding the short tubing, and RJs weigh-in method. Fine-tune to manufacturer's chart.

High SC

@ June 6, 2013 10:46 PM in High subcool

Hmmm. A drier on the low side? Did you have a burn-out? Is the drier next to the compressor where it should be, or in the line set? A burn-out would be the only reason you should have a low side drier, so it is possible the system was not cleaned up adequately, which would again lead us to a possible restriction. I would check your PD (a suction drier will have a service port for that very reason). If not, temperature is the way. If you have to start over, follow RJs lead. Best of luck.

High SC

@ June 6, 2013 7:02 PM in High subcool

I would check for non-condensables and restrictions first. Do a static check; with the system off for at least 20 min., your head pressure converted to temperature and your ambient should be the same. If higher than ambient you have something inside that shouldn't be there, causing an abnormally high SC. If OK, check for restrictions. You started that process by mentioning checking temperature or pressure drop across the drier or driers. If three degrees or less the driers are happy, so you might try to recover some refrigerant to see if this helps. Look for kinks in the tubing or an incorrect size. Watch your superheat too!!!!!

Air Cleaner

@ June 4, 2013 2:04 PM in Air Purifier

This is the issue that is largely ignored in our industry, for reasons I will never understand. I hope this clarifies that last sentence for you. Each and every component you connect to a furnace or air handler creates an air flow restriction. Ducts, fittings, registers, grilles, and accessories such as cooling coils, humidifiers, and your air cleaner or filter. This is fine, as long as you design for it. Think of it this way: if you have a 28' camper, you're not going to tow it with a Ford Ranger, so you wouldn't buy the Ranger after the camper unless you have a fascination for high blood pressure. If you add an air cleaner and the blower wasn't "prepared" for the added restriction, then something is going to suffer (that Ranger can't get the camper up the hill). This means poor heating and cooling performance, a high energy bill, and an air cleaner that doesn't do the job you expected. When you find out what is medically causing your SO's cough, contact me so we can revisit this. Also drop me a line if I didn't clarify the pressure drop issue enough to suit you.

Air Purifier

@ June 3, 2013 10:36 PM in Air Purifier

Don't spend any money on a product that someone "thinks" will help. Follow Bill's lead and find out what is causing the medical condition and work toward the elimination of the source. IAQ is a carefully planned process of filtration, purification, disinfection, and humidification. It hardly ever is just throwing an air cleaner on your system and hoping for the best. Additionally, if you don't consider the pressure drop created by the air cleaner and how it affects your blower and duct system, you're painting yourself into a horrible corner.

Cold Temps

@ June 3, 2013 10:01 PM in cold temps

Assuming you're talking about residential units, low ambients have a greater impact with a fixed metering device. Since there is usually very little load, a machine with a FMD is in danger of not having a high enough superheat to avoid liquid refrigerant coming straight from the evaporator into the compressor. TXVs are more forgiving, as their job is to ensure a constant superheat at the compressor. Now to the other side. If the SH is too low, the compressor has to work very hard to mash liquid (instead of vapor) enough to raise the refrigerant temperature high enough above ambient so we can de-superheat it in the condenser. Since we can't change liquid into a liquid, you can imagine what your high and low side pressures will be, as well as a practically non-existing SC. If the compressor doesn't give up chewing on all of that liquid, it certainly will running when it doesn't have any work to do.

Sizing Reply

@ May 25, 2013 12:48 PM in Mitz sizing thoughts

I see your point. And, it seems as if the HO is trying to stop a bullet with a bullet.


@ May 24, 2013 6:46 PM in Mitz sizing thoughts

You should feel comfortable with the size determined by your load calculation, provided it is ACCA Manual J or their sanctioned partner. Oversizing a mini-split with DC inverter technology could mean lack of oil return to the compressor during low load hours.


@ May 17, 2013 9:40 AM in Survey!

I believe you will see most manufacturers are going to 15' from 25', so check the unit manual. But that is not lineset length; it is the factory refrigerant charge. You need to add "x" ounces per foot over 15'; again, that info is in the manual. Lineset TEL is in the manual too. It might be 60' for some models and 50' for others. Beyond those limitations you need the software we talked about or call your distributor. Regarding your question about sub cooling numbers: if you have 10 degrees of sub cooling, that means your actual LL temperature is 10 degrees cooler than your LL PSIG converted to temperature. This ensures your 100% column of liquid at the TXV. For example, if your LL is 295 PSIG with R-410A and your LL temperature is 85 degrees, then you have 10 degrees of sub cooling.
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