How was this unit originally equipped? TXV? Use only a TXV OF CORRECT size. In refrigeration if you have a 6000btu rating you do not use a 1/2 ton valve you use a 1/4 ton (3000btuh) at most and would need consulting with an engineer to arrive at the correct valve.
SO was the TXV the other fellow replaced an OEM valve? If not this may be the problem as most TXV's off the shelf are designed for walk-in refrigeration Not Reach ins. An OEM valve may be the trouble here.
Now not to stress the TXV but also the compressor (what was the original model?) Make sure it is designed for the particular heat range and size for this application. As you probably know 1 size compressor designs for AC will not be OK on Refrigeration at same BTU rating.
Call Del field and verify what they are using or recommending for this unit. model and Seal no required and the existing model and SN.
Also to my knowledge a receiver is not required and in fact will only add to your trouble. Receivers are for changes (wide differences) in condensing temperature and pressure. Never saw an application for one with a condenser designed from factory for indoor use with either type of expansion device.
If you need Del fileds number email me at
[email protected] and in th subject line enter delfield?.