Extreme pressures

[singaman]

I have this Daikin ducted unit that will trip with low suction pressure(15 PSI ) and high discharge pressure(300+PSI). Had replaced compressor and filter drier .Suspect blockage of R22 in evaporator unit. How to confirm my judgement and is there a strainer at the evaporator unit? Can someone advise me. Thanks

[The MG Pony]

there will be a valve or capilery, if capilery it will be at the condencer, if tev(Txv) there may be a strainer, how ever there aut to be a filter drier in line near the condencer. At this point you will see clear signs of sweating/frosting on the filter drier or where the blockage is.

start at the discharge and work your way along the system, you will find it this way.

[passandscore]

If it is a TXV, check your superheat. Adjust valve as needed. Before any of that I highly suggest some light reading on the following.

http://www.emersonclimate.com/Documents/FlowControls/PDF%20resources/2006FC-174R1TXVre-article.pdf

[The MG Pony]

befor you even think of touching the TXV super heat adjustment the box/room most be at opperating temp, other wise you'll under feed at load when in opperating temp.

I will go so far as to say NEVER TOUCH SUPER HEAT! seting on a txv unless it is well proven to be the issue, way to many fiddle with it for no sound or logical reason and this will be no end of missery for you!

let's start with this.

Condenser: Is it clean and in good shape?
Condenser outlet: Is there a shut off valve? is it open all the way?
Past the valve: Is there a F/D? or is the expansion piston placed here or a txv?
If it is a straight pipe to the A Coil/wall unit do we have a filter drier there? cap tube or txv?

If txv what is the type and brand (Some have a clean out screen inside them! is the F/d sweating?

like I have said we need to start at the discharge and work our way along the line!

[singaman]

Thanks gentlemen for the replies. I have to add that there is non of those items you mentioned. There is only capillary tube at the condenser side.

[passandscore]

Cap tube systems can be tricky. I would start, like MG Pony suggested and check the condenser. Is it clean and in good shape? . It does seem like you may have a blockage in the capillary line. Due to your low suction pressure and because of your high discharge pressure the blockage may be apparent. A visual inspection of the cap tube for frost would be the indicator. If you see no frost then perhaps the system is slightly overcharged with a minimal restriction. It wouldn't hurt to confirm that. If you choose to remove the gas, weigh it and confirm the charge. This would also be a good time to pressure the high-side with nitrogen and see the rate at which the low-side equalizes. If the cap tube is the problem and it gets replaced, it is recommended that the oil be replaced also.

[The MG Pony]

I'd agree with replacing the oil if it has been opperating in this condition for some time, and install a filter drier befor cap tube as there is a reason it plugged to begin with!

Cap tubs can plug very easy if the system was worked on any time recently, even from the manufacturer if don poorly will plug after a few months of use.