Hello.
We have a Lennox HP26-042-12P Heat Pump that needs servicing. I'm just wondering if our A/C contractor is being straightforward with us.

Two weeks ago, all was working fine with the system, and while replacing a sheet of siding on our home, I very stupidly drove a nail through the A/C supply. In a matter of seconds, it drained all the coolant from the system. Yes, I'm an idiot, which I keep reminding myself, although I'm usually a pretty careful do-it-yourselfer. Anyway, the A/C contractor came immediately, fixed the puncture hole and completely recharged the system. But, another problem has since developed...

In north Florida, we can still have some cool nights, so I've recently been alternating heat at night and cool during the day. As of a few days ago, the heat pump/compressor failed to come on at all, in either heat or cool mode. Another call to the technician revealed that we need a new TXV valve which, unfortunately, means losing (and replacing) a lot of the coolant we just replaced with the previous repair.

Before this valve stopped working, the only thing unusual I noticed after this incident/repair was that the heat pump was operating a little unusually... it would come on and heat the home, then turn off while the blower continued to circulate (all normal), but then the heat pump would then turn on again for a few minutes and turn off again. I didn't notice this happening before the service call, and I didn't notice anything unusual with the A/C.

My question: is it just incredibly bad luck that this valve has failed now, so soon after my mistake, causing us to have to pay to refill the coolant twice (over $700 a pop)? Or, is it possible that the valve has failed as a result of something done/not done during/before the re-charge?

Of course, they're trying to talk us into a new system, but we're not ready for that as the Lennox is only about 9 years old.

Thanks much.
Kevin

Wow, sorry about the nail in the side.

The contractor must be referring to the outdoor txv since he has to remove all the refrigerant. Otherwise if it was an indoor txv change out they could save the gas as the compressor can pump all the refrigerant into the outdoor coil and can be sealed in there temporarily. (called pumping it down)

Now you mentioned the compressor not coming on at all? That is not typical of a TXV problem, at least not initially. A side symptom is the high pressure switch will come on (open) to cut off the compressor, if that txv is clogged up, but I am surprised the compressor will not operate at all. Even after the unit has sat for awhile (pressures stabilized) it should come on albeit for a short period possibly.

Threre are a lot of questions you could ask your contractor to get more info.

1. Find out which TXV is bad (indoor or outdoor) and how they diagnosed that with a cut out compressor.

2. there are other possiblilites. Maybe they overcharged it with refrigerant and it is cutting out on high pressure.

3. Ask what the superheat/subcooling is and learn yourself so you know you are not getting a line.

If you can get a little more info it would go a long way to finding some real answers for you.

Here is a vid on TXVs and it is acutally on a lennox indoor coil and a pic of a lennox outdoor txv.

video on you tube (https://www.youtube.com/watch?v=I4sOBj62f8g)

photos of an outdoor txv on a lennox unit (halfway down I think) (http://www.thermal-medics.com/a-c-image-glossary/)

Judging by your intermittent problem in heating it sounds like that outdoor txv was getting clogged up and your unit cutting out on high pressure in heat mode.

To directly answer your question yes there is history on the outdoor TXV being a problem (if that is the one they diagnosed)
And yes when they opened it up maybe they did a less than stellar job pulling a vacuum, not changing the filter drier, not brazing with nitrogen flow etc that contributed to it clogging up for good.

You also said it does not run at all in cooling mode either? Even after sitting for a couple of hours idle?

Thank you so much. Answers to your follow-up questions, to the best of my ability:

-It is diagnosed as being the outside TXV. Sorry to have omitted that information before.

-regarding the overcharging, I specifically asked about that, having read that non-starting is sometimes a symptom of over-charging. The tech insisted that was charged to the correct amount.

-a drier was put on after he re-charged (from the puncture repair). There was not one before.

-in re-reading his notes on the receipt, I see where he indicated "system shuts down when high pressure reaches 400 psi."

-And correct, it wouldn't run in cool mode, even after sitting idle overnight.

Presently, the tech 'reset' the board, giving us A/C on the condition we don't switch back to heat. He said switching to heat would shut down the SXV again. It buys us some time to get better educated, I guess.

Wow, you have to give him points for at least giving you the reset and not just leaving with the disconnect and you with a bid for a new unit..

Outside of being overcharged or really looking at that txv (sensing bulb location) etc they might have it right.

Sadly they have to blow the charge in this case. The TXV screen may be just clogged too. I have taken them out and cleaned them and even just tossed them if the system is old and they are falling apart.

I did run across one unit that was just slightly overcharged and cut on high pressure when the heat ran on no-so-cold days (if that makes sense).
The subcooling was only 3-4 degrees higher than called for in the charging chart at that temp so I pulled a little gas out (dropped the subcooling) and it ran like a champ. Just saying it happens.

Good luck with it - stupid nail...

I would go with a second opinion too and by the way 're-setting' that board is not to tough to do if you haven't figured it out yet.

Extremely helpful. Thank you very much.