I am running into problems with a Lennox heat pump that shows vacuum on low side and 0 on high side in heat mode. In air conditiong mode however I do have a compression ratio. Now for some background. This call started in july of 2010 with a no cooling call. I determined that the failure was a short to ground on the compressor. i ended up replacing the compressor and installed a new liq line filter drier. I did not do an acid test which I realize I should have done. I brazed in while purging with nitrogen perfored a standard leak test and pulled a 500 micron vacuum. Weighed in virgin r-22 according to manuf specs. Cycled in ac mode and test system was running perfect. Then the cold weather hit and the system does not heat. found both units operating but pressures showing 0. reclaimed r22 and found still had same amount from comp replacement. check id and od txv and found no problems. At this point i decided to change the txv and reversing valve which i know the rev valve is rarely a failure point. moved system into shop replaced parts leak check and now perform triple evac. re installed system and still have the same problem. Any suggestions would be appreciated as the cust has been extremely patient but i fear that will run out. I do have recorded pressures and temps if needed.