I have a split system in a condo with the condensing unit on the roof 70' above the evaporator. My question is regarding charging the system. It uses R410 and has a TXV. The Carrier guide says that for a 3/8" liquid line I need to add .60/oz of refrigerant per foot above the 9 oz factory charge. 0.6 oz/ft x 70' - 9 oz = 33 oz. My problem is that this formula doesn't change depending on if the condensing unit is above or below the evaporator. Because my evaporator is well below the condenser, the weight of the refrigerant alone will increase the pressure at the TXV depending on the height of the liquid column in the liquid line at the TXV. At higher pressure, for a given refrigerant temperature, the refrigerant would be more sub cooled and less likely to flash at the TXV (right?). Also, most of the liquid line is inside the building so it will tend to be at about 76 degrees (leaning toward more subcooling, right?). How can I possibly charge this system correctly as it seems to me the "standard" Carrier long line guideline will overcharge it with the evaporator well below the condensing unit.
Great get-together from both of you . The respond of you most of diy hvac techs take that 25 minutes literally very seriously . they let the compound gauge to -30 and that's it . the idea is that system is under vacuum. no micron gauge no oil for the vacuum pump not change but not oil at all. I have used the vacuum further avay from the vacum pump not to 500 mic but 250 all of them triple evacuation for mostly old line-set or ac not splits but good practice. I m following you two for long time Bryan Orr too. If any one of you need a helper for free if you came to NY for me will be like working for Willis Carrier. Good tips god experience. Thank you
In Mitsubishi Mini Split Heat Pump Manuals, it says you can Pressure test for only 15 minutes if you have the pressure at 500 PSIG. I have found that the pressure modulates a bit sometimes for the first few minutes after first putting in the nitrogen, and I think that may be due to temperatures inside and outside of the building or home that may differ from each other or from the temperature of the gas in the tank. Therefore, I consider the 15 minute test way too premature. I think that short test might only tell you if the refrigerant charge wont leak out in a few weeks. Am I right in thinking that to really know for the long term that the test should be minimum 1 or 2 hours?
The modulations are probably not due to temperature differentials, dry nitrogen P/T is not that sensitive to notice on a gauge, unless it's freezing outside/warm inside and the lines weren't well insulated. That's most likely the nitro making it's path through the linesets before it equalizes. In NYC, the engineer's inspection asked 601 psig for York/Hitachi, monitored for 30 minutes. I don't think that's enough either, so we let it hold overnight through the temperature changes to be sure we won't have to carve out the walls later.
i cant fathom someone prefering any other metering device than txv/eev. dont have much experience with pistons but cap tubes are a nightmare to deal with.
Nothing worse than asking someone who doesn't know or has bad incomplete info, and when you are learning can contaminate your knowledge. My rule of thumb is to ask more then one source and that goes true for a 30 sec google check.
i looked up to someone in the second company i worked for and assumed everything he said was 100% correct. It wasnt until later that I found out that the procedures he was doing was just getting him by and not really good for the systems. of course there was no youtube or looking it up online back then. Yes i agree, dont just listen to one person and research yourself!!!
I have a question. If you shorten the line set on a Mimi -split how short can you go? Example if you have a 25’ line set and you cut it down to like 12’ will the system be over charged?
Can I in an A/C condenser replace two single capacitors, a start cap of 30 uF, and a run cap of 5 uF with one dual capacitor 30/5 uF? I wonder if I'd get an answer to my question. I subscribed, maybe I get the answer in the next session.
You mention a book called Vacuum for the Service Engineer… I cannot find that title anywhere. Any suggestions where I should look? Is that the correct title?
I do believe that fast evacuations leads to impurities left in systems and should perhaps allow for longer evacuation for degassing copper line sets and etc.
When you do the nitrogen pressure test you may still have some moisture in system. If it holds nitrogen pressure, then you know you are tight. If skipped nitrogen pressure test, just doing vacuum, and keep seeing vacuum decay you don't really know if it is due to an actual leak or just moisture slowly coming out of the oil. After 20-30 minutes of continued vacuum decay failures, time to punt and do a nitrogen flush to help sweep freed water vapor out of system. Nitrogen cannot help get moisture out of oil, only vacuum will do that, but it will help sweep freed water vapor to get released out service port.
I find that oh lets say 5 out of 10 txvs have failed do to contamination ie sludge or debris of some sort from improper service/installation practice. But lets not forget about cap tube rubouts from poor factory installations as well
Ok so here is a solution on 1 port mini splits, If we have a flare fitting on the liquid line leave the fitting loose and purge the nitrogen thru the fitting then tighten down. Then start your purge to slight positive pressure and then perform vacuum.
As for the subcooling question, in residential systems there almost always a target subcool on the outdoor unit with more modern equipment. But i get what he was saying, alot of rtus ahus in our commercial world do not list it at all, not even in the ioms. Aaon is the majority of what i work on for rtus, and they dont specify, tech support says 10 though so about normal. Some trane units will give a subcool target while others give a charging chart based on head pressure only, the chart will say if you have 320 head psi then your liquid line should be this number and add or remove if on either side of the curve. If you get it rite on the money with that chart, sometimes it equals to be 18 to over 20 degrees of subcooling. Which throws me way off, if i walked up to a unit w that high sc i would think someone overcharged. But in those cases i believe they want it that high do to type of system,2 compressors,one evap,one liquid line, one suction, no solenoids, 2 txvs, one compressor can flow through 2 txvs at one time,or both compressors, so maybe they want to ensure subcooling is there for when only one comp is running. This is typical of trane makeup units and it throws many of us for a loop cause we dont get taught about these oddball setups. Ill also add that airflow is the same in alot of multi stage equipment regardless if one or two stages running. We need some teaching on these if either of you have experience with them. Great video as usual
One more thought on the last question of low DT… where are you reading supply air temp at? If at a register where ductwork is in the attic, you may be getting heat transfer in ductwork that is throwing off your numbers. Thanks for all your vids! Have been VERY helpful.
high tech-inverter hyper heat pump and low tech-single stage nat gas or propane boiler or forced air furnace. Obviously hot water piping and circulation would be preferred in a greenhouse.
Have you seen where the farmers bury corrugated pipe and use it as duct work to accept and reject heat as the ground is always 50ish F about 10 feet down? I doubt the efficiency of something like that but the simplicity is appealing. They use a bunch of 6” fans which can be replaced easily if they fail. I think the boiler sounds very appealing and so does the gas furnace. Thank your response.
We measure the electrical resistance of circuits and components almost as often as measuring voltage for alternation current. Resistance is used to determine if a switch is closed, open, or pitted also if motor windings and wiring are intact!
I've been out in the field doing installs and service and on call for 15 years and had my own company. I spent plenty of time in hot attics and wet tight crawlspaces. Ive felt time frames for jobs, and fixing in the middle of the night, but I understand what it looks like in these q/a videos. We are trying to encourage techs to do the right things and to give perspectives to answer questions, thanks.
Today they overcomplicate everything. Back when I owned a small HVAC business mid 80's - late 90's nobody used nitrogen to pressure test (or when brazing for that matter). When installing a new system or after a repair, we pumped the lines for about 30 minutes and watched the manifold gauge for about 20 minutes after shutting the pump. If it didn't move, all was good. Haven't you noticed how long all those R22 systems lasted?
R-22 used mineral oil and yes that mineral oil didn't clean the oxidation from the walls of tubing like POE oil does now in R410a and now R32 and R454B, thanks.
