TEV "Sticking" Power element.

[Grizzly]

Hi Guys.
Today I had a problem with a TEV sticking where on a correctly charged system.
The Suction Pressure and Saturated Suction Temp
Continued to drop!
Eventually causing the system to shut down as it reached it's Low Saturated Suction temp setting.
Having confirmed a fully loaded comp and a full sight glass with no flashing.
I came to the conclusion there was an issue with the expansion valve.
Here's the question.
To resolve the problem I applied some heat to the power element (where the capillary line meets the body).
As I did this both the suction pressure and sat suc temp started to rise.
I was then able to adjust the expansion valve to raise both the pressure and temp!
Prior to this adjustment had had little or no effect.

So given I have heard tales of power element blockages be it gas or water vapour, causing them!
And as I have had success using the heat trick before.
Could these "causes" be true?
Or has anyone got a better explanation?
Cheers Grizzly

[Gary]

Something to check: The TXV bulb should be mounted with the cap tube end upwards, else it is possible for the charge to migrate from the bulb to the power element.

[US Iceman]

Was the power element recently changed (before you got there) Grizzly? In some cases it might have the wrong charge for the application.

Or, the push rods might be sticky!

[Brian_UK]

Sounds like a charge migration as Gary says.

[hd88]

Something to think about. you applied heat and the valve opened. That tells you that the valve is working. Bulb location is important also.The problem will come back...all you did was heat it. Could there be alot of moisture in the system? moisture will freeze up in that valve and block it up, and heat will let it pass. This was just a thought.........

[lowcool]

i would be chasing moisture,generally the power ellement is above the bulb.but in this game anything is possible.
grizzly maybe warm the body away fom the power ellement allowing heat of body to loosen any ice at expansion point before the full impact of heat hits the power head.
any chance of removing valve when this condition occurs for a visual check?

[Grizzly]

Thanks for the comments guys!
Basically I have covered my back.
By advising the customer that my "repair" may or may not be temporary.
Adding that if any issues return then replacement would be necessary.
My question was,,
Had anyone else resolved TEV issues by careful use of applied heat?
Gary's point about charge migration is were I was leading the question.
(Or any other physical condition that could apply)
Would it be possible for a systems pressure to drop to the point where, say the phial charge migrated to the power element head?

"We" seem to be changing TEV's or their power elements more when there has been a loss of refrigerant.
Resulting in chillers running for long periods on low load / pressure.

Thoughts anyone?
Cheers for input so far guys!
Grizzly

[Gary]

If the bulb is mounted upside down, when the suction line warms, the rise in bulb pressure pushes the liquid through the cap tube into the power element. It doesn't come back until the bulb is colder than the power head.

[BESC5240]

Charge migration mostly occurs on thermostatic elements with limited charge, like elements with MOP charge.
Temperature difference (bulb warmer then valve) does the rest.
Example: winter time (no airco needed - plant shut down) TXV in cold ambiance - well insulated bulb is (slightly) warmer.
In spring, plant is started up. No charge in bulb to create pressure/force to open TXV. Compressor shuts down on LP. Heat up TXV (warm air, warm water, no direct flame ...) : problem solved.