TXV vs Piston valve
I'll try to keep this brief even though it is a long story.
Approx five years ago I replaced an old R22 system with a new Carrier 410a system (38TXA with CD5A coil) for my small split-level home in the DC burbs. Worked OK the first summer but barely made it through the second summer. Since then we've had problems every year, usually the coil freezing up at some point (we're good about the filters). Over the course of numerous tech visits over the last three years we've been told: possible line leak, poor duct design, line should have been replaced when system was replaced, too little refrigerant, moisture in line, etc. Have tried to educate myself about things that can go wrong when replacing R22 system with 410a system, but it is overwhelming. The latest tech came out yesterday because the coil was freezing again (after working well all summer). This time the story is that the system will never work well unless we install a TXV kit ($REMOVED) to replace the piston-type valve that came with the system. Says the TXV is required for Puron systems and the original installers should have known. After dropping $REMOVED last summer on a leak test (no leaks found in coil or compressor) I'm a bit reluctant to drop another $REMOVED on what is essentially a new system. If a 410a TXV is required for this system why would Carrier sell the system without one? After hearing some many different explanations I just don't believe it, even though the tech said he was "100% certain" that was the problem. Can anybody out there tell me if I'm just getting another runaround?
Last edited by HeyBob; 08-03-2008 at 01:42 PM.
Reason: Removed Pricing
ok. i'll try to help out. not sure of the credibility of ur a/c techs...
the condenser system is the one that comes factory charged with 410 a or r-22. the evap coil should come with the piston metering device and a kit to swap it out for r-410a. it is for the manufacturer and the dealer to make sure that it is all supposed to work together. If the problem is with the TXV, you should be able to call the Co that did your install in the 1st place to come back and repair their mess up.
get the condenser model and serial number, the air handler model and serial number and the txv numbers.
call the manufacturer. the phone number should be in one of the user guide manuals from ur unit. call them and ask them what expantion valve will work for ur system. tell them what you have and see what they say.
if they won't talk to you because you are not a dealer or a tech, tell them your a tech for the Co that did your install.
first of all 9xx is way too much money to change to a tsx thats likely almost enough to replace the entire coil. Now to some explaining the piston is to control your airflow so that you dont get too much freon in your system. On the other hand the tsx is a device that likewise does the same thing. On your part you may be right if it was needed it would have been in the box.. But i've worked around some not to bright guys who dont put them in. Check your system make sure they are the same ton size. Next look on your AH and condensor and see if the small liquid side has a nut on it if it does it is alread equipped and all you need is matching pistons *check to see there are pistons in there. and the need for it isnt a difference in r22 n r410a its the design of the system p.s a tsx kit is in the 2 digits and work is in the hour or less if your me
Hope it helps a lil
this is the scary part...
if i was fixing it id flush the lines because r22 and r410a mixed could cause likewise problems. Then match the pistons...
You already have another thread covering this topic.
You need to remove the pricing references in your post before a moderator does.
No reason why a matched split system from the factory, regardless of refrigerant, should not work correctly with a piston metering device. TXV devices do a better job of metering the correct amount of refrigerant for a given heat load, but are not a cure-all for evaporator icing problems. I've seen plenty of TXV evaporator coils frozen solid in my time.
Since you have a history of both icing problems and closing off vents in the house, do not do any more of the latter. Leave all vents open. You may have an air balance problem on top of an airflow problem if you aren't getting even cooling from your system.
Do you realize you just told a home owner to remove the nut at the coil to check the piston in a charged system? Talk about not so bright!, I believe That is why this is not a DIY forum. What do you think will happen when he removes that nut with a charged system? As to less than an hour if it were you, maybe true but not less than an hour to do it properly.
Originally Posted by jb00gz
A. R410A systems do work with pistons. Different manufacturers have different metering methods.
More likely your problem is an air flow issue then a metering device issue.
Many techs don't kow how to check air flow, and just keep adding refrigerant, and condemning other parts.
Ignore the guy giving you cost opinions and DIY instructions.
He'll just get you in trouble.
Give use the full model numbers of your coil, outdoor unit, and furnace.
Also, how big is your house. Size of ducts, return and supply. Number of them.
Please review the rules re' pricing in your posts as well as starting multiple threads with the same basic subject matter.
You need a little education on what a customer should be telling distributor about a system that YOU have never seen.
Originally Posted by fadelG
'Life begins with the journey each day'
There are numerous things that could cause an evaporator to freeze. If you are having problems trusting your contractor you may want to look elsewhere. A more reputable company with more reliable techs. As far as TXV vs pistons, TXVs are more efficient than pistons from the fact that they regulate the flow of refrigerant solely off super heat. In low load conditions there is a possibility of pistons flooding the evaporator and slugging a compressor.
## + years in the field never made you a know-it-all This industry is far more diverse than you are
as a simple explanation... any AC unit has to control rate liquid refrigerant is delivered into evaporator coil.
it's done with a restriction just before the evaporator coil.
one type has a fix orifice that can only deliver liquid a set rate. (different types fixed orifices used)
other type has a variable orifice (TXV) uses a sensor to adjust rate liquid is delivered.
both types can have high seer values. TXV equipped systems have advantage of being able to adjust (superheat) for slight changes to operating conditions, but have higher mfg costs.