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TXV valve faulty ?

540itouring on Sun March 23, 2014 6:58 AM User is offline

Year: 1994
Make: Jaguar
Model: XJS V12
Engine Size: 6.0L
Refrigerant Type: R134a
Ambient Temp: 14
Pressure Low: 1.6bar
Pressure High: 12.1bar

I have had a leak on the TXV valve by the bulb and so had lost the gas but before this worked very well . The car was off road in my garage over the winter and found this leak last week and ordered a replacement TXV Valve. I made a error when I pressure tested with OFN while I was looking for the leak and tested at about 15 bar instead of 10 bar. This slowly dropped due to the faulty valve and when I fitted the new TXV I have no leaks and so gave a vac for 40 mins and a full recharge of 950g . The system started up fine with the compressor cycling and vents cold and return pipe from TXV to compressor with condensation forming. After the system had run for a while the compressor did not cut out and runs all the time and the vent temp was about 6deg . The TXV valve when I got it was not packed well and wonder if this could be due to a stuck valve that is partly open ? Would the compressor reed valves be damaged by 15 bar pressure test ? The compressor sounds fine and pressures stable and just think the TXV Valve is not regulating the flow , so would that cause the problem I have found ? I know I was lucky not to blow the evaporator ! Can these valves be tested off the car in any way as I can only think this is the fault. I know they can get stuck closed or may be full open but do not know if they can also stick partly open with no regulation.

Edited: Sun March 23, 2014 at 7:19 AM by 540itouring

540itouring on Sun March 23, 2014 7:50 AM User is offline

I have just started the car again after its cooled down and with low of about 2 bar and high of 10 bar and 1500 rpm the compressor is now cycling again. The air intake to cabin fan tem is about 22deg and the cabin vent tem is about 9 deg. All these tests were in the garage with bonnet open so no ram air to condenser. Could this now have stabilised after the new install or do you think I just needed more rpm ? I expect the best test is take it for a drive but the car is off the road until I re licence it in May but like to get it all ready for when I will be using it again.

Thanks for all your help. This is the first time I have replaced a TVX valve so unsure if all valves are the same spec or do they settle down after a while ?

540itouring on Sun March 23, 2014 11:03 AM User is offline

I have just started the car again after cooled down and now runs perfect with compressor cycling quite even. The only thing I can think of is that the new TXV valve was sticking as it was new and dry and now the pag oil has worked into the new valve has now become free and so works as normal . Has any members got any explanation on new TXV valves and do they take a while to bed in ?

This was all with engine idling at about 800 RPM.


Thanks for your help.

Edited: Sun March 23, 2014 at 11:05 AM by 540itouring

bohica2xo on Mon March 24, 2014 4:49 PM User is offline

I would suspect the cutout switch if it quit cycling.

A TXV sitting open would drop the temps only as long as the cycling switch kept the compressor on.

I have had flaky cycling switches before. Pay attention to both the cut-in & cut out pressures as it operates. A switch that has a lot of hysteresis or one that does not repeat well should be replaced.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

540itouring on Mon March 24, 2014 7:59 PM User is offline

Hi , thanks for your reply. This car only has one dual pressure switch (high & low) in the high pressure line to the txv valve. This switch I think cuts compressor out is gas is below 2 bar and also cuts out if over pressure due to no condenser cooling etc so I think the climate control ecu controls the clutch ?

The evaporator also has a thermistor telling the ecu module the evaporator temp . I can not see how a pressure switch in the high liquid line would be able to cycle the compressor unless this switch is triggered during normal operation to cut the compressor off ?


please can you confirm if I am right or not


Thanks

bohica2xo on Mon March 24, 2014 9:13 PM User is offline

If you only have an HPCO, then whatever controls the evaporator temperature is where the fault is.

When you mention cycling on a US forum, we presume the system to be a more common CC type with a LPCO that serves both as a safety & the low temp limit.

The TXV does not have anything to do with cycling. Thee system cycles off because the TXV can not throttle down far enough to prevent evaporator icing at low ambient temps / low airflow.

Pull the thermistor if you can reach it easily, and test it. Perhaps it is full of leaves or a spider nest. I have found both in MVAC sensors before.

.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

540itouring on Tue March 25, 2014 4:14 PM User is offline

ok thanks for all the info and will check to see what I can find.

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