FAQs on A/C & heat pump Thermostatic Expansion Valves - TEVs:

This air conditioning repair article series explains the function and installation of all types of refrigerant metering devices, beginning with the most-common thermostatic expansion valve or TEV (or thermal expansion valve) that controls release of refrigerant into the evaporator coil of an air conditioning or heat pump system.

Q&A on AEVs, TEVs, Manual Valves, Cap Tubes

These FAQs about TEVs and other refrigerant metering devicves were postd originally at THERMOSTATIC EXPANSION VALVES - be sure to see that article too.

[Click to enlarge any image]

Schematic of a thermostatic expansion valve courtesy of Carson Dunlop Associates.

On 2018-03-11 by (mod) - trouble with Trane heat pump

My sympathy for what sounds like a costly mess.

At the first repair the tech surely confirmed that the system was working properly, right? Proper refrigerant charge, checked temperatures, pressures, and heating or cooling function, right?

I am slow to blame the tech, but in fact soldering a system can leave debris in piping that can then foul a TXV, especially if soldering was near the TXV and moreso if no filter/drier was installed.

If the aux heat never kicked in I'm left confused - was that because temperatures never required the aux heat or because aux is not working either?

On 2018-03-11 by Dexter

Residential Trane heat pump -11 yrs old without issues. HVAC tech found a very small leak in a pipe going to the indoor unit during a routine maintenance visit. Paid $1300 to have leaking pipe soldered, and refrigerant evac/recharge.

After service, heat pump ran continuously, never saw aux heat kick in and cool air came from vents; however,
attributed this to colder than average temperatures for a couple weeks.

Realized that heat pump wasn’t functioning when weather returned to normal so HVAC company sent tech back. Told that TXV was bad and not metering properly and quoted another $2000 to replace TXV and evac/recharge refrigerant.

What is standard procedure?

Were TXV’s checked at first repair? Could the initial repair, and evac/recharge have damaged the TXV?

Had a working Heat Pump prior to routine maintenance inspection, a non-working heat pump after ‘leak’ repair and now a request of another $2K, to return to a working heat pump. Thanks for any guidance.

On 2016-07-23 by (mod) -

Sounds as if the compressor is not running or the TEV is not working.

On 2016-07-23 by Altaf Ahmed

Pressure not building up on high side and low side after charging R-22 into the package unit

On 2016-01-10 by amir

My queation was about capilary tube between bulb and diaphragm of txv.
why we dont insolated this tube?

On 2016-01-09 by (mod) -

Amir if I understand your question the tube is a temperature sensor that must be touchng the refigerant tubing or coil

On 2016-01-07 by amir

Sorry
why we donot insolate that tube?

Why we donot the tub between bulb and txv?

On 2015-07-22 by (mod) -

Anon:

Ask your HVAC service tech to look for a problem with the A/C unit condensate handling system or for cooling coil icing.

On 2015-07-22 by Anonymous

Something leaking under the heat & air unit. Unit starts and stopped are noisy and rattles system.

On 2015-07-08 by (mod) -

Yes

On 2015-07-02 by Anonymous

could exspansion valve be bad if heat pump isnt cooling and refrigerant level is right

On 2015-06-24 by bob

R410A system. Low side pressure 50psig, high side 110psig. added a small amount of refrig, and low side went to 150psig, high side still 160psig. the system has an orifice for metering. Could orifice be missing?

Reader comments:

(June 30, 2011) James Wrobel said:THERMOSTATIC EXPANSION VALVES is an extremely useful article. Well done.

(July 18, 2011) rhomz said: thankz for this article,i have learned a lot

(July 19, 2011) Ervin Berrios said: Thanks guys, this explanation is very helpfull to me, as I'm learning and working in AC in residential. Now I have a very reliable information to provide to my customers

(Sept 13, 2011) George Martinez said: Thank you very informative article.

Reply:

Ervin and others, thanks for the nice notes. We welcome questions and critique - together we're smarter than anybody alone.

Question: icing at TEV

(Mar 4, 2012) Dangeh said:

Hi..What to do if icing at TEV,HP and LP in normal working pressure

Question: Home AC unit began rapid on/off cycling.

(July 1, 2012) Ruth F said:

Home AC unit began rapid on/off cycling. Unit is a Bryant 5 ton about 5 years old with no prior problems.

Repairman removed 2# of Puron refrigerant and unit operated fine again.

Did he fix the cause of the problem or merely treat a symptom which may recur at a future time? Could there be a TEV problem or coil clog?

Question:

(Dec 11, 2012) Ralph said:

We are looking at purchasing a grocery store. The store has a new refrigeration system and cases. The one of the expansion valves feeding a row of reachin cases has a screaming sound. Do you have ideas as to this problem?

Reply:

Ralph, most likely the TEV is screaming in distress as refrigerant flows through a partly obstructed or dirt clogged or iced valve. If the refrigerant charge is correct and the problem continues I expect your service tech will replace the valve.

Question:

(Dec 21, 2012) Mohd. Anwar Hyd India said:

Hi In 11Tr DX model 2 Circuits In UPS Room In 1 circuit ice formation from suction line Circuit 1 LP Press 56 HP Press 240 & Circuit 2 LP Press 50 HP Press 245 Compresser is ZR72 Scroll is working normal in Indoor motor & Belts is ok how adjustment expansion valve Please advise me thanks with Regards.

Question:

(Apr 1, 2014) Richard said:

can a metering cap be changed out?

Reply:

Richard, IF I understand the question correctly you're asking if some TEVs have replaceable parts. Yes. Else the whole TEV is replaced.

If you are asking if the capillary tube (which is a simpler refrigerant metering device than a TEV) can be replaced, also yes - it's a cut and braze job plus some more work to evacuate, then re-fill, and clean the system refrigerant piping system.

Question:

(Apr 26, 2014) Anonymous said:

sir, we have facing problem of compressor trip on High pressure condenser coil is clean,drier is ok so can we adjust the expansion valve setting pl.suggest.

Reply:

Sorry Anon I don't have enough information about what you mean by "compressor trip on high pressure" - I suppose if the expansion valve is defective, jammed, dirty then that might cause an improper pressure balance but there are other possible explanation such as a compressor motor failure or voltage problem that need to be considered.

Question:

(Apr 29, 2014) Stephen Moore said:

We have 2 ac units in a brand new house. Within 10 days of moving in, both units froze and the repairmen said the expansion valves needed to be replaced on both units. The system ran for a week and one unit froze again with the same issue. The repairman ordered another expansion valve.

These are brand new units and I find it odd that we had 3 valves fail already. Is there another issue that may be going on with the units that is causing the valves to fail?

Reply:

You're right to question authority on HVAC, though they could indeed be perfectly correct, it's likely there's more to the story.

Other causes of freeze-up that might lead to replacing all the TEVs would be

- dirt in the system messing up the expansion valve operation.

- batch failures: my invented term for a production run of a part that repeats the same mistake in manufacture, so all or many of the parts made at the same time all fail

- There are other possible causes of freeze-up: a fan failure, too-slow air movement, wrong filter, constructed ductwork, inadequate return air, low refrigerant charge.

If nothing else was changed when the TEVs were replaced and if the system has continued to work since then, that's a vote for having made the right repair. I'd hope that the repair also included replacing the refrigerant filters in the system at the same time.

Question: selecting the proper thermostatic expansion valve

(June 19, 2014) Philip said:

how do i get the right expansion valve to mentain (+5 temp.) on the surface of my evaporator

Reply:

Philip you can bring your specifications to your HVAC supplier; some TEVs are adjustable for fine tuning as well.

Danfoss (2005) points out that there are the following data points that go into selecting the proper TEV:

1. Refrigerant gas used
2. Evaporator capacity
3. Evaporating pressure
4. Condensing pressure
5. Subcooling temperature requirements
6. Pressure drop across the TEV
7. Internalor external refrigerant pressure equalization requirements

Each of the manufacturers of Thermostatic Expansion Valves provides catalogs of TEV models, features, specifications, and intended applications. at THERMOSTATIC EXPANSION VALVES and in theReferences or Citations of that article we list some sources of TEV manufacturers offeringcopies of TEV catalogs and specifications and installation or repair guides. .

Question: how to solder TEVs or TXVs on HVAc equipment

Bubs said:

Can you solder 95/5 on txv's in leu of silfos?

Reply:

Bubs

If you take a look at the solder sold by companies who provide TEVs (thermostatic expansion valves) used on HVACR equipment, such as Danfoss, you'll see that only two types are even listed: 15% silver and 45% silver solder brazing rods.

Keep in mind that silver brazing is much stronger than lead or tin soldering of copper and that it is done at a higher temperature - your ordinary LP tank soldering or even MAPP soldering tools are not hot enough. We use acetylene.

Question: definition of "TXV" or Thermostatic Expansion Valve or Reversing Valve

(Oct 9, 2014) DODOU NJIE said:
BOTTOM OF COMPRESSOR TOO COLD
WITH CONDENSATION ON THE OUTSIDE OF THE
COMPRESSOR.

(Oct 25, 2014) Anonymous said:
I have Rheem AC/HEAT PUMP.The cooling mode works fine,but the Heat Mode won;t provide heat. Could the problem be the TEV and/or Reversing Valve?

(Oct 25, 2014) Anonymous said:
What is TXV?
Dick

(Jan 28, 2015) Anonymous said:
Henry.what is thermostatic expansion valve

Reply:

Anon, the reversing valve is a good guess.

Dick, if you refer to TEV that's short for thermostatic expansion valve. Some may write it TXV

Henry

The thermostatic expansion valve or TEV is described in the article above. Please take a look and then let me know if the article is unclear.

A reversing valve is a different component: this valve reverses the direction of flow of refrigerant in an HVAC system such as a heat pump, permitting change between cooling mode and heating mode.

...

Continue reading at THERMOSTATIC EXPANSION VALVES - topic home, or select a topic from the closely-related articles below, or see the complete ARTICLE INDEX.

Or see these

Recommended Articles

• CAPILLARY TUBES
• REVERSING VALVE on HEAT PUMPS
• REFRIGERANT PRESSURE READINGS & CHARTS - home
• THERMOSTATIC EXPANSION VALVE TEV INSTALL, DIAGNOSE, REPAIR

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THERMOSTATIC EXPANSION VALVE FAQs at InspectApedia.com - online encyclopedia of building & environmental inspection, testing, diagnosis, repair, & problem prevention advice.

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INDEX to RELATED ARTICLES: ARTICLE INDEX to AIR CONDITIONING & HEAT PUMPS

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