View Full Version : pistons and txv's
07-05-2006, 06:02 PM
can a 1.5t condenser calling for a size.50 metering device be use with a 2.0t airhandler with a txv metering device.....any help would by appriciated
07-05-2006, 07:13 PM
newguy, match your refrigerants, e.g. R-22/R-22, R-410A/R410A, you can not match a R-22 txv with a R410A condesner, or vice-versa. change out your txv to match the tonnage and type of refrigerant, shouldn't have to change out the coil.
[Edited by re2ell on 07-05-2006 at 05:17 PM]
07-05-2006, 07:39 PM
I would do it.
The slight risk from my point of view is that if the valve is oversized it may "hunt" or over cycle, but 1.5T CU and a 2T AHU w/ 2T TVX should work just fine. They only come in 1/2T sizes. This 1/2T AHU upsize will be the wrong why to go if you have a high latent load as this bigger coil will run at a higher SHR, higher EST, Higher ADP on normal blower tap.
You can also play with bulb placement before you throw in the towel on a "hunter" and pull the valve. Don't forget to add a Hard Start (PR+SC) to that compressor because the fixed metered set-up probably came with a PTCR start and it will start loaded now that you TXV'ed it. If it's a scroll and I guess today it would be than you don't need a start kit unless the lights are dimming or they have low utility voltage "problems". Oh, that TXV should be ext eq. too.
BTW, to this day I don't know the logic used to match piston sizes. Are they matched to the evap coil or the CU? The obvious truth is that the evap and the CU together form a single "system capacity". There is no evap capacity and separate CU capacity after you put them together as there is now one single system capacity. That system capacity needs a fixed metering device (if you must) idealized for peek demand conditions and since mother nature strictly recognizes ARI Region IV rating points that condition will be exactly 80/67/95. The truth is your going to trim the charge for target SH per EWB and ambient DB so SC will float to meet the needs of the target SH (with in reason). Let me know if I'm crazy here because there is no perfect charge for a fixed metered system that serves a variable lift application. The best you can do it's optimize it for where it will delivery the best capacity, therefore EER, at peeking cooling demand which is for the most part what the OEM I&O charging instructions tell you but in a way that prevents you from actually understanding anything beyond the rote procedure, and then there is Lennox where they smoke crack and tell you to charge a fix metered system by SC (huh?) and a TXV by approach (why?).
I don't have much faith in fixed metering and as far as I can tell, no OEM, and no contractor has a good enough excuse to install one since about 1950 (except heat mode for reasons of high HGT at high lift / low ambient with R22 as it is not a good low temp, high CR refrigerant).
I would defer this over all question of fix metering a system (not a component) to Prof. Sporlan. TXV is the easy answer here.
If you have to swap the valve you will still learn significantly for having tried and succeeded on the rebound, most will not even try, but instead tell you what can't be done.
07-05-2006, 08:36 PM
i was asking this question bacause he system is already put together, it was vacuumed as specified, 500 microns.... the brand is carrier tha models are, condenser: nac018akc3, and is stamped that is charged with r22 and requires a piston size of 50, the airhandler is model ebx2400a with a txv metering device, when the system is first started up everything works almost fine but i notice the suction line is not as cold as the one in my house (which cools really good)also after it has reached the desire room temperature and shuts down then the thermostat calls for cool again and the fan outside runs but not the sompressor(hard start kit needed0.....the thing that i think might be happening is that the txv valve is letting liquid pass back to the suction line and that's why is not so cold and might be flooding the compressor(am i right thinking this)........THANKS FOR THE RESPONSES SO APPRICITE YOUR INPUT/suggestions
07-05-2006, 08:50 PM
hummm, you are not using the words of the initiated. One must speak of super heat, sub cool, evap saturation temp, cond saturation temp,... to get answers to refrigerant cycle questions round here.
Anything less is "beer can calibration".
BTW, not knowing the numbers, your system may be flooding back and therefore the line feels colder.
Also, if the outdoor fan is turning and the comp is not the CB will soon trip unless maybe that comp is off on internal OL.
Maintain your curiosity, but back up and let someone more invested make a diagnosis. If he doesn't speak in the terms of my first sentence than he should be dismissed as well.
[Edited by mdman on 07-06-2006 at 04:55 PM]
07-06-2006, 01:35 AM
newguy, the txv tonnage needs to match the condenser tonnage. more than likely you will need to add start assist, and lastly, bad policy to compare temperatures of different units.......think about it and don't allow yourself to be entrapped thinking all units should run the same.....that's what i call 'wrongful thinking'.
07-06-2006, 02:29 AM
Most of the TXVs I see in newer equipment are ballance port type TXVs for multiple tonages. The parker ones come in 2 sizes, 1-3 ton and 3-5 ton.
A lot of the modern TXVs are designed so they will work with a pressure drip as little as 50 psi, so usually there is not really an issue. Trane actually has ARI listed matchups with 5 ton coils on 2 and 2.5 ton outdoor units that do not require a change of TXV.
Even if it is not a ballance port multi tonage valve, it is not likely there will be any significant issue with a 2 ton valve and a 1.5 ton outdoor unit.
07-06-2006, 06:18 PM
very much appriciated , thanks for your sharing of knowledge and you opinions
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