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87mustang
04-08-2005, 05:57 AM
I have a situation that we need to control the suction pressure (keep it elevated) during hot gas defrost. This is a retro fit install in order to get the room into the 34 degree range. Hot gas will be piped into a Tee set between the Sporlan distributor and the orifice. A liquid line solenoid valve will be present but, not de-energized during defrost.
The evap is an existing air defrost type ( 100,000 BTUH).

I need to keep the suction pressure elevated during defrost only. I was thinking about a suction stop evap pressure regulator but, then I woild only pump down the system and cycle off at the low pressure switch.

Any ideas?

US Iceman
04-08-2005, 04:17 PM
Hi 87Mustang,

Do you have one evaporator and one compressor for this system? Is your intent to provide hot gas defrost for the evaporator, or, hot gas bypass to control the evaporator pressure? You mentioned hot gas defrost, but also wanted to get the room in the 34F range.

Can you provide more details please?

Thanks,
US Iceman

frank
04-08-2005, 07:48 PM
With hot gas defrost you also need to consider protecting the compressor from excessive back pressures.
A rule of thumb is to install a compressor pressure regulator if you install an evaporator pressure regulator

Temprite
04-08-2005, 10:53 PM
With hot gas defrost you also need to consider protecting the compressor from excessive back pressures.
A rule of thumb is to install a compressor pressure regulator if you install an evaporator pressure regulator

Hello frank.
I am working on a freezer at the moment that has a CPR attached.
It has hot gas defrost.
Refrigerant is r404a.
Looks like someone had screwed with the settings because I could not get compressor suction over about 25 psi and unit wasnt working properly.
Opened it up slightly and pressures and operation were now much better.
Just wondering if anyone new correct pressure and method to set.
Even though system now achieves correct temp I am not entirely convinced that it is correct.
Thanks.

wambat
05-08-2005, 03:20 AM
I have a situation that we need to control the suction pressure (keep it elevated) during hot gas defrost. This is a retro fit install in order to get the room into the 34 degree range. Hot gas will be piped into a Tee set between the Sporlan distributor and the orifice. A liquid line solenoid valve will be present but, not de-energized during defrost.
The evap is an existing air defrost type ( 100,000 BTUH).

I need to keep the suction pressure elevated during defrost only. I was thinking about a suction stop evap pressure regulator but, then I woild only pump down the system and cycle off at the low pressure switch.

Any ideas?

You can put a solenoid operated bypass around the EPR valve with a relay wired in parallel to the LLS with NO contacts to by-pass solenoid so when stat is satisfied relay and LLS are denergized and bypass solenoid will energize for pump down

tralex
05-08-2005, 07:25 AM
Hello 87 Mustang
Perhaps this link be useful for you
http://www.sporlan.com/90-40.pdf

Best regards