Heat pump problem

[Darc]

Hi all.

i am currently working on a 30Kw cooling capacity email/york package aircon unit and was hoping that someone might be able to confirm my speculation as to what is wrong with it.

When operating on cooling the unit operates fine but when switched over to heating mode I am getting very low suction pressures and high discharge pressures the line from the outdoor unit TX Valve also ices up from the TX. When i wind the TX valve all the way out the suction pressure increases momentarily and then drops back down....If i wind the TX all the way in the system pulls a vaccum

All filter and coils are clean....I am speculating that the TX valve on the outside unit may be duff.....??

Thoughts?

[nike123]

Hi all.

i am currently working on a 30Kw cooling capacity email/york package aircon unit and was hoping that someone might be able to confirm my speculation as to what is wrong with it.

When operating on cooling the unit operates fine but when switched over to heating mode I am getting very low suction pressures and high discharge pressures the line from the outdoor unit TX Valve also ices up from the TX. When i wind the TX valve all the way out the suction pressure increases momentarily and then drops back down....If i wind the TX all the way in the system pulls a vaccum

All filter and coils are clean....I am speculating that the TX valve on the outside unit may be duff.....??

Thoughts?

Check this thread (http://www.refrigeration-engineer.com/forums/showthread.php?t=11903&highlight=adjust)!

[Brian_UK]

It sounds like a typical fault with the reversing valve not changing over.

Check temperatures across the valve in both modes.

[Darc]

Thanks for the relies so far guys!

I dont believe that it is the reversing valve as the unit changes over from heat to cool and there was no temp diff across the reversing valve....

Thanks for the link to the TX valve discussion too! I have been reading through the posts and there is definetly some good info in there....

[nike123]

Do you have sight glass in front of heating txv? Is it full? Is the line in front of TXV warm or mild to tuch? If yes, than check your heating txv power element correct functioning!

This is from another forum (hvacprotech):

Checking the Power Element of a TXV

Refrigeration systems which are operating with a higher than normal evaporator superheat value can be the result of several system problems. On systems using a thermostatic expansion valve (TXV) as the metering device, one cause could be a loss of charge in the bulb of the TXV. This is due to the fact that the refrigerant charge in the bulb of the power assembly is the opening force of the TXV. When a loss of charge exists in this bulb there is not enough force to throttle the valve open to its correct position.



The following procedure can be used to see if loss of charge in the bulb of a TXV is the cause of a higher than normal evaporator superheat:

On a valve with an external superheat adjustment, turn the adjustment nut to the full counterclockwise position. Verify that the evaporator's superheat is still too high before proceeding to the next step. If the evaporator's superheat has changed to a much lower value, try adjusting the valve to obtain the correct superheat value for the system.

Remove the bulb from the suction line and hold it in your hand for several minutes to warm it up. Observe the suction pressure. If the valve has a refrigerant charge, you should see an increase in the suction pressure.

If no change in the pressure occurs, it is reasonable to conclude the assembly has lost its refrigerant charge and needs to be replaced.

Some TXVs have a removable power assembly which can be replaced instead of changing the entire TXV. If the power assembly can be removed, the bulb charge can also be checked by trying to depress the diaphragm with your thumb. You should not be able to depress this by hand. If you can, the assembly has lost its charge.

[Darc]

Turns out it was the Power Element after all. Thanks everyone for your responses.