Problematic unit, please help

[lees8110]

Hi all,

I am having a bit of a problem with a package unit on r407c. I have recently repaired a leak and recharged the unit but now 2weeks down the line the unit is going out on low pressure AND high pressure.

I have a good air flow over the evapourater and condenser.

I am getting a suction pressure of around 3.5 bar but this then drops to about 1 bar slowly as the condenser fan comes in and out until the lp switch triggers. and I have measured the evap outlet pipe surface temp of 13 degrees. this gives me high superheat (correct me if im wrong).

Does the system seem to have sprung another leak? or could I have a problem with the tev underfeeding?

Thank you in advance for anyones views

[Gary]

Is it cap tube or TXV?

What is the subcooling?

What is the superheat?

[lees8110]

It is TEV, I was getting a subcooling measurement of approx 10 degrees

and a superheat of around 17 degrees

[Brian_UK]

^ We assume that you are talking Centigrade readings.....

[lees8110]

^ We assume that you are talking Centigrade readings.....

Sorry, yes that is correct

[brunstar]

it does sound like you could have a blocked filter before or after the TEV depending on what mode you have it in or the TEV is getting jammed.
What model of unit is it as if it is a multi speed condenser fan motor one of the relays could be gone on the pcb so it thinks it is running in medium fan speed but the fan speed turns off.
what mode are you in and what is the model number?
You should check the cycling of the condenser fan motor in all speeds and also chck for icing at the TEV.

[Gary]

Yes, it sounds like some sort of intermittant blockage. Or possibly moisture freezing in the TXV and then defrosting when the high side pressure/temperature rises (fan off).

[Magoo]

I would be de-canting system charge, evacate system. And start again with fresh system charge. From memory R407C is a ****tail blend, so which bit did you lose with the leak.
Just a thought. I stand to be corrected.
magoo

[lees8110]

Thanks for the input so far guys

I re-charged with new r407c with it being a zeotrope I didnt want to take any risks,

There is slight frosting around the t.e.v and the pipes branching off it too which made me think the t.e.v is ok (might be wrong).

As for the condense fan It is a lennox package unit LHA088 model Ithink the speed is single speed (again I mite be wrong), I have replaced the Full PCB as I had a spare to hand,to eliminate this.

[tmm]

less8110, in one of the previous posts you noted a supertheat reading of 17C. Given that the system was operating as intended this would be a cause for concern since the almost universal setting for most TX valves is 6C. Remenber below 4C the differential is too slight to allow the valve to operate as intended.
I suggest that you revist the site and having established good running conditions check the value again- with a view to adjusting towards the 6C value. During this process conformation of improvement should be evident with better heat rejection from the condenser and improved duty over the coil.
The risk in not checking is that the superheat cooling provided for the compressor is not adequate and therefore you could have a failure in the near future.
If you can recheck and post it would help any additional thoughts.

tmm

[cool_tech]

hi ,
sounds like there might still be a little bit of moisture in the system maybe? did you use a vac stat? ester oil is very hygroscopic .
let us know how you go with it.
ct

[lees8110]

Ok guys, I fitted a new TEV to this last week and it seems to have ran ok since, the pressures settled to a constant and it was cooling away unlike before!

I also noticed when I had removed the old tev the part number didnt match up to the new one Lennox had sent me, having given them the serial number of the unit, and after a bit of research it turned out the tev fitted should have been on the cond coil (heat pump, dual tev). So makes me wonder if this unit has ever cooled properly until now!

Thanks for all the input guys

[lees8110]

Two/three weeks down the line and it has gone out on LP again!!!
What is wrong with this unit!!?
According to the client this unit has run fantasticly in the previous hot weather we have just had until now!
I had a quick play with the unit and I noticed if I run the unit in heat ( bypassing the evap tev) it runs perfect and then when I switch back to cooling after doing this it does run ok until it reaches desired room temp then when it starts back up it goes out on LP again.
This sounds to me like the one way check valves could be sticking??? or do the symptons give something else off?

Please help if anybody could offer their advice

Thanks Lee

[Gary]

Evap air in temp
Evap air out temp
Low side pressure
Suction line temp at TXV bulb

Cond air in temp
Cond air out temp
High side pressure
Liquid line temp at condenser outlet