1.OK I dont know where to put this. But something popped up in my head. the purpose of the expansion valve is to regulate refrigerant flow right? Im a little lost.. Tell me if im right if the expansion valve is stucked open it would causing refigerant flow to constantly flow through the lines so it would build up excessive pressure? so high side pressure would always be on the high side right? Now if its stucked closed. It would act as a restriction to the system and lower system pressure (high side low)and end up frosting up the lines right?

Is this right?


2.Both of these system would cause the compressor to turn off because there is a high pressure and low pressure cutoff switch?

 

Best explanation I have seen...

Many different types of TXVs. The temperature differential of the evaporator inlet and outlet typically determine the opening and closing of the TXV seat to either add (flood) refrigerant flow or constrict (starve) refrigerant flow to the evaporator. Refrigerant levels will affect the TXV if considerably out of range as the TXV is limited in opening size but it is much more tolerant of a charge level off a small amount. Keep in mind that the refrigeration process is incredibly simple. When the refrigerant changes state from liquid to gas its ability to absorb heat (latent heat)without increasing its sensible (measurable) heat increases exponentially. The TXV cannot detect latent heat but only measurable heat so what it is looking for is when the refrigerant enters the evap in its liquid/vapor mix form and absorbs all the latent heat it can, as it turns (boils) into a pure vapor. It then begins to absorb measurable heat (superheat) so the TXV is always trying to make sure just the right amount of refrigerant based upon sensible heat is released into the evap to completely absorb all the heat it can and have just a touch of superheat to prove that all latent heat has been absorbed plus this makes the vapor less likely to turn back into a liquid before reaching the compressor and damaging the compressor valves. If the TXV starves the evap the liquid boils completely off before reaching the end of the evap tubes resulting in high superheat and poor cooling since very little of the coil is being utilized. If the TXV floods the evap the liquid never boils off and absorbs the latent heat as it should, resulting in no superheat and of course poor cooling. As you can see a properly operating TXV controlled system is far superior to the fixed orfice types. You will find most of the fixed orifice systems are 10 or less SEER

Hope that helps. 94

 

how does this answer my question? i need to know if i am right about the pressures when its stucked closed/open.

 

"If the TXV floods the evap the liquid never boils off and absorbs the latent heat as it should, resulting in no superheat and of course poor cooling." Flooding occurs if expansion valve is stuck open open.

"TXV starves the evap the liquid boils completely off before reaching the end of the evap tubes resulting in high superheat and poor cooling since very little of the coil is being utilized." If valve is stuck closed.


If a txv is not working correctly and is "wide open", it may in some cases (due to higher suction line pressure) hinder the addition of more freon. However, a good technician would know if the system charge is incorrect or if the txv is stuck open by looking at the subcooling and superheat numbers. Charging of this type system is done by checking subcooling and adjustment of the txv (if adjustable) is verified by the degrees of superheat.

If on the other hand the txv is stuck closed, the suction line pressure will be too low, the high side pressure will also be low, but the superheat will be too high. To an untrained eye, the system will "look" undercharged. At this point an inexperienced person will add a whole bunch of freon in hope of bringing up the suction pressure. This will result in an overcharged system with low suction pressure and high side pressure that is now much too high. 94

 

now can you interpret that in your own words. since where if i was a customer and didnt now all the technical terms.

 

If expansion valve is stuck open you do not get colld air.
If expansion valve is stuck closed you will not get cold air. 94

 

i was looking more like what will be the pressures be for each side.. and why???

 

I beg to differ with your summation that if the txv is stuck closed or sensing too much superheat that the discharge pressure will be low as well. when the txv closes it acts as a restriction thus increasing the discharge pressure.