Airedale low pressure fault

[glenn1340]

Hi Guys,
Hope one of you can help. I`ve got a problem with an Airedale CHS6 that trips on LP (1bar) in heating mode. Ambient`s -1c at the moment. It runs for about three seconds then goes out on LP, as there was no time to take any temperatures or accurate pressures I thought it easiest to remove and weigh the correct amount of refrigerant in as I had found a very small leak beforehand. Alas no joy, it`s still tripping. The pressure after the filter on the return line from the indoor unit (in heat mode remember) at tripping is about 5bar and rising, and after the TXV and reversing valve 1bar. Now here`s my thoughts: Am I`m looking at a faulty TXV? (no difference if I hold the bulb in my hand) I`m hoping it`s not a duff reversing valve as that`s going to be a pig to get to.
What do you think guys?
A virtual Xmas drink`s on me for the one that comes up with the answer....sod the expense, drinks all round!:D

[nike123]

Outdoor fan is OK and spinning at full speed?

[glenn1340]

Hi Nike,
Thanks for the quick reply,
The fan doesn`t get a chance to run as unit trips after three seconds or so, that`s why I think it could be a restriction in the suction line. However, as it runs for such a short time I can`t take any accurate readings.
By the way, it ran ok when was last on site ( not working on this unit then, just happened to notice it running ok)when the ambient wasn`t so low so I think there was just enough refrigerant flow to keep it from tripping. Now the ambient`s dropped that may not now be the case.

Thanks again Nike

[nike123]

At -1°C ambient i would expect much higher evaporation and it is certain that you have some restriction at suction side (when heating).
It is probably not reversing valve or compressor since you have good compression ratio.
I would try to run cooling mode and see if the problem is still there and that would help in locating where is restriction.

[glenn1340]

I had another look today and did what nike suggested and ran in cooling mode, problem still remaining.
Turned the unit back to heating mode.
I fitted a line tap valve between the outdoor condensor and the reversing valve to measure the pressure, here`s what I found: 5 bar approx before the valve and dropping to .5 bar and tripping after the valve on the suction into the compressor.
I`d have thought the pressure before the valve should be simmilar to after the valve. But hey, this is what this forums for, to pick wiser brains than mine.
Now, I reckon I`m looking at a u/s reversing valve but I just want to see if any of you have come across this before I change said valve as this job looks a right pig to do.

Cheers guys

[The Viking]

Yepp, shouldn't see any pressure drop across the reversing valve (Assuming that you look at the right pipes)

Before you change the reversing valve, try to gently tap it on the end with a hammer.
These valves have a 'floating' piston inside them that is operated by pressure and any debris in the system will cause the piston to get stuck.
If you are lucky a gentle tap will free the piston and give you time to schedule a proper repair/clean up.

Good luck

[nike123]

http://www.achrnews.com/Articles/Feature_Article/6306a3596885a010VgnVCM100000f932a8c0____
http://wayneshirley.wordpress.com/2008/02/07/troubleshooting-heat-pump-systemsreversing-valves/