Why mismatch system failure after 10 years.

[SpinnerCO]

Cased coils started frosting over during the past month so we had tech come out to inspect. The following system components were installed in April of 2002.
Trane XL13I Model TTX3048A1000A
Trane UV80 2 Stage VS FUI UD100R9V5J
EZ Conv CDS HP/AC coil TXCO54S3HPCO R22
Aprilair Humidifier
Trane Programmable Thermostat
Alco TXV Valve C860272-P07

Tri level home with apx 2500 sq feet. We have never had any problems with the system until now.

We had a tech come out for inspection and he states that the outdoor unit, which is R-410, is incompatible with the interior R-22. After lots of discussion about what that means, how inept the prior install company was, and how we have been sucking the life out of the X13I..... we are finally left with recommendation that is high in cost.

My question is.... why would a company mismatch the system. Was the R-22 cheaper to install?

Why has the system worked for 10 years and we only now have a problem?

Do we have to replace the interior AC coil unit with a R-410 compatible unit?

Could it simply be a faulty TXV? Can we replace it if it has failed, and keep the mismatched system?

From what I understand, R-410 is running through the R-22 lines. Is this a just a non-optimal situation or is it a dangerous situation?

I'm not looking for absolute cheapest way out of this hole.... just looking for a reasonable solution.

[carmon]

the frosting coil could be caused by lots of things... did the tec say why they were frosting

[SpinnerCO]

He did say that he thought the TXV valve was malfunctioning and this allowed in too much coolant. Something along the line of too much coolant for the evaporator coils to evaporate. Checked all filters and they were clean. Fins on inside unit were clean. Fins on outside unit clean. We talked about number of returns, and vents. He did mention that we should not close any output vents, and switch to cheap filter during summer months.

[beenthere]

Sounds like you had a selling tech. Probably gonna need another tech out to find the real problem. Might need to call a different company. An over feeding TXV won't freeze the coil.

[chuckcrj]

That thing is practically new. If it worked fine for 10 years, the mismatch is a non-issue.

You may have a refrigerant leak somewhere. Or a bad TXV, but not for the reason he told you...

[SpinnerCO]

FYI
When he hooked up his metering hoses outside... he said what was "coming in" was fine... what was "going out" was half of what it was supposed to be.

[carmon]

I would call for second opinion....... something fishy here.....

[BaldLoonie]

Is that a 4TTX3048?

Was the TXV on the indoor coil changed to a 410 TXV? He may be assuming not.

I'd be surprised if a mismatched TXV would keep you cool all these years but I guess it could have worked enough to do so. 4 tons on 2500 sq ft is a lot unless you are in a very hot climate or poor insulation.

[catmanacman]

Im not sure if the coil is a txv coil im thinking it is a piston coil so it would have a external txv i do not beleive the system is mismathed in the early phase of Trane 410a units the coils used were there r22 coils im not sure this tech is familiar with trane units

[SpinnerCO]

Yes, it is a 4TTX unit outdoors. Sorry, the invoice I was pulling the numbers from is cut off on the side.

I believe we went with the larger 4T unit because of our desire to get adequate AC on the upper level of the house. It was either booster fans in the ducts or larger outside unit. I'm beginning to believe we made a poor choice there.

I've attached some shots of the inside unit, including the TXV valve. Some of the paperwork I have for the system does state "TXV with internal check valve".

Tech's line of thinking was because there was no air flow obstruction, that it had to be a faulty TXV. He said "head pressure is normal and suction pressure is low".

Sometimes it seems like it's another language you guys speak!

I do note that the illustration on our paperwork of cased coils shows a TXV in a completely different place than the physical location on our unit.

I do not know if the original install switched out one kind of TXV with the one the system came with. Are there different TXV's for R-22 and R410 setups?

The system begins to ice over after apx 60 minutes of operation.

[BaldLoonie]

In those days, the TXC-S was the high efficiency (meaning BIG) R22 TXV coil. The RXC had the 410 TXV on it.

[SpinnerCO]

Okay... my cased coils (R22) came with a R22 TXV.

So my question now is, if the TXV fails, and it came with my cased coils.... can I replace just the TXV (for R22) and not the TXV and the coils?

I really didn't want all this nomenclature and HVAC speak to take up part of my brain... but alas it is what it is.

[carmon]

the txv could certainly be replaced....