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I installed a 18,000 btu ductless system. Manual said if lines are over 16 feet you should add *****, Lines are 25 feet. I hooked guage to high and low lines and the pressure was 115 on low and 125 on high. Does anyone know what pressure the unit should be.
Thanks
David
It depends on whether the compressor is running or not, the ambient temperature will also affect the pressures.
When I started the unit up the 12x24 foot room was about 80 deg. f It got down to 70 deg in about 15 or 20 min. Then we turned the thermostat way down so the compressor would run. So with 70 deg. temp and the compressor running. What should the pressures be.
Thanks
David
im not sure which grunaire unit you installed.. was it an HX inverter series or an HR series 13 seer??
I have 2 of the inverter type units in my test lab and one severely modified unit running in my home...
all 3 of the units I had different results... which says to me that they are not very careful about the amount of refrigerant that is pre-charged into them..
I simply followed pressure temperature charts and measured my superheat / subcooling (im sure you are familiar with that)
I used the included 25 foot lineset on all 3 of my units (including the modified unit)...
1] Unit one was low on refrigerant.. I added 4 ounces of liquid by weight to that one
2] unit two was dead on.. not a bit low, not a bit over..
3] unit three I added 2 ounces of liquid by weight
now onto the interesting part... all 3 units seemed to perform perfectly well even with the variances in refrigerant... none of them had the tendency to freeze across the 4 way valve.. and none of them ran super high hot gas line temperatures...
remember inverter units vary the speed of their compressors.. so you will want to crank the unit down to its max lowest temperature.. set for high fan force and let it run at least 15 minutes.. you may need to open a window to create a load on the evaporator...
the Chigo service manual for these units has a pressure temperature chart in it as well... ...
-Christopher
Imagine that you have an empty container. You pull a vacuum on that container and then you start adding refrigerant vapor.Quote:
Originally Posted by drose300
The pressure in the container rises as you add more refrigerant vapor... until liquid droplets begin to form.
As soon as there is both liquid and vapor in the container, the pressure has nothing to do with the amount of refrigerant in the container and everything to do with the temperature of the container.
Two containers sitting side by side will have the same pressures, even if one of them is 1/4 full and the other 3/4 full. That pressure corresponds to the temperature.
In an empty system, when you charge beyond the initial small vapor charge, there is liquid and vapor in both the evaporator and the condenser.
The pressures have little to do with refrigerant charge and everything to do with the temperature and volume of air flowing through the coils versus the pressure changes being exerted upon them by the compressor.
What should the pressures be? That depends upon the temperature/volume of air flowing through both coils, the rate of refrigerant flow through the metering device, and the speed/efficiency of the compressor.
cadillackid thanks for the reply. could you explain how you charge a unit by the temp. chart, superheat/subcooling. I work in a maintenance dept. When we get ac service techs to look at our ac units. If they are low they just add ***** till the line gets cold. I would like to get it closer to the right amount than that. by the way I have the same unit as you, set up the same way. 25 ft lines
Thanks
David
hey there i can send you the Chigo service manual for the unit if you like... calculating superheat and subcooling on these things is tricky as they use a "flooded coil" technique... I wont go into why they use it.. the service manual has a pressure temp chart in it.. however you will need to take the outdoor unit apart if you want to measure temp right at the expansion device.. the expansion device is in the outdoor unit... that is why both lines are insulated and also why both lines are cold... the small line (I normally would call the liquid line) is actually on the low pressure side of the system on this unit...
let me know if you like to have the manual.. it covers ore than one unit, however the inverters are covered.. as well as info about the control cycles in them as well... its obviously been written in chinese and then run through an english converter... they did convert temperatures to degrees F but left pressures in Kpa....
the graphs in the manual have various scenerios of different dry bulb and wet bulb temps...
there is nothing refrigerant-wise you can do on the indoor unit..
also just adding refrigerant till the line gets cold is a BAD way of doing it on a minisplit.. the other things is charge only liquid form for 410a and charge VERY slowly.. because there are temperature sensors on the evaporator coil.. 4 of them to be exact.. evap inlet, evap center, and evap exit.. then room temp. introducing refrigerant too fast will affect those temperatures which will affect compressor output and expansion valve position..
-Christopher
-Christopher
Thanks Cadillackid, I would like to have the manual. How could you send it to me? what would I need to do?
Thanks
David
Hey Cadillackid, Is it possible for me to get the service manual from you.
Thanks,
Chad
I could use a Grunaire service manual. Desperate to figure out why units will not work properly. Have deep vaccumed - recharged and STILL dual mini-split won't work. One unit freezes you out - won't quit running - other unit won't cool - no matter what temps are set. HX units
I could use a Grunaire service manual. Desperate to figure out why units will not work properly. Have deep vaccumed - recharged and STILL dual mini-split won't work. One unit freezes you out - won't quit running - other unit won't cool - no matter what temps are set. HX units
I'll take one too if you have the chance.Quote:
Originally Posted by minisplituser
I've been told that they come pre-charged for 15ft lineset and the local HVAC guys who install a number of these say that most of them come pre-charged to handle a range of lineset lengths. (the single indoor/outdoor units). They claim that they work fine without varying the coolant in line lengths of anywhere from 15ft-50ft.
Evidently the acceptable range is large enough that a few ounces here or there doesn't impact performance drastically.
The only way you are going to know absolutely what is in there is to pull it all out and weigh it. I'm not an HVAC guy but take what I say with a grain of salt but Gary is right-on in terms of his physics. Pressure won't tell you jack about how much is actually in the unit.
I'm installing mine next week and the plan is to physically get the thing installed, wired and plumbed and then have the local HVAC guy come and pull a vacuum on the indoor/lineset for 15 minutes. Cap it and watch it for another 15 minutes to see if we are loosing any vacuum (leak detection). Then I'm just going to have him open the valve and let the 410A into the system. I'll use the soap solution to double check the flares for leaks but other than that..... I'm not going to monkey with trying to add/subtract 410A unless there is a performance problem once it is running.