i have a r22 low temp rack set up for hotgas defrost using a liquid differental valve. this rack is set up with air reclaim but its primarly used for dehumidification and limited times for heat. apparantly they had some glass door reach in cases icing up. what they determined was the head was crashing so low when it was in reclaim and trying to defrost a sys at the same time,that it wasnt do much of anything. they said thee head was dropping from 190 down to 90, so someones solution was to put in a relay that would shift the three way heat reclaim valve back into refrigeration mode when something would go into defrost. my question is this wouldnt it make more sense to install a holdback valve to keep your head up and would there be any merit in setting up the hold back valve to increase your head while in defrost from say a 190 setpoint up to maybe 225.