Walk in Freezer

[smythers1968]

Went to a walk in freezer that had stopped working a couple days ago. Found that the high pressure cut out had been tripped. Tried to reset it but I couldn't reset it. So I put a jumper in and checked pressures. HPC was set at 350 and head pressure was 375. Outside ambient was 105. Also found that the fan/defrost temp sensor have some how come apart. So I wired the evap fans to direct power so the fans would run all the time. Got the freezer down to 28 deg

Today I replaced the dual LPC/HPC and the fan/defrost sensor. Reset the defrost timer and got it going. Had it down to 24 deg in about a half hour.

My problem is this when I replaced the LPC/HPC the low pressure cut out was set at 0 and when the system went into defrost and the LLS closed the condenser would still run. I couldn't find any specs on what the LPC should be set at. I set it at 25.

I have never come across this before and wondered if anyone here had any ideas.

Thanks Jeff

[smjrusche]

What kind of refrigerant and what temp r u trying to hold. Did u have gauges on and if so how for down did it pump when u pumped down. What kind of compressor is it also.

[smythers1968]

What kind of refrigerant I think it was 22. Couldn't read label

what temp r u trying to hold. 0

Did u have gauges on and if so how for down did it pump when u pumped down.

When it pumped down suction went to 0 and liquid was close to 375


What kind of compressor is it also. Scroll[/QUOTE]

[2sac]

So the compressor won't pump down to zero? Why won't it pump dowm? Bad pump? Capacity? You couldn't find any specs on what the control should be set at? Unless it's being used to control the box temp, there are some pretty standard settings. If you're storing anything but ice in the freezer, 24 degrees is way too high. If the defrost termination switch was shorted, I can almost guarantee there are other issues which you will or will not find when you go back and the coil is frozen.

[K_Neil]

Pump down system should pull down to 0 psi easily when LLS is deenergized.
Check suction pressure with suction valve closed to make sure the compressor can pull down. Close LPC or jumper contacts. Then watch suction pressure with compressor off to see if crankcase pressure changes atall. If it stays put ok. If it climbs there's compressor valve problems.

[2sac]

Scroll probably has an internal relief so the pressure will jump once deenergized

[smythers1968]

So the compressor won't pump down to zero? Why won't it pump dowm? Bad pump? Capacity? You couldn't find any specs on what the control should be set at? Unless it's being used to control the box temp, there are some pretty standard settings. If you're storing anything but ice in the freezer, 24 degrees is way too high. If the defrost termination switch was shorted, I can almost guarantee there are other issues which you will or will not find when you go back and the coil is frozen.

The compressor will pump down to zero. The problem is that the LPC is set at 0 and even though the compressor will pump down it will not shut off.

The question is that, Why is the LPC set at 0? If the LLV closes and the compressor pumps down to 0 and the LPC is set at 0 and the compressor does not shut off then, Why is the LPC set at zero?

The LPC is not used to control box temp.

I already have an idea that the defrost timer is not working correctly and causing some of my problems.

[smjrusche]

I may be wrong but scrolls are not designed to run below 0psig somebody correct me if but If that is so u can't do a pump down test on a scroll u have to contact the manufacturer to do efficiency test.

[smythers1968]

I may be wrong but scrolls are not designed to run below 0psig somebody correct me if but If that is so u can't do a pump down test on a scroll u have to contact the manufacturer to do efficiency test.

I think you are correct and thinking about it I think it is a Recipt

[smjrusche]

U set the lpc at the setting that u feel as necessary below normal operating pressure to shut down condensing unit unless u r using it for temp control which u r not. In my opinion above 0pig when possible. If u have a ll this will help to keep outside contaminants outside the system and shut it of with a positive peas on it. IMO

[smythers1968]

U set the lpc at the setting that u feel as necessary below normal operating pressure to shut down condensing unit unless u r using it for temp control which u r not. In my opinion above 0pig when possible. If u have a ll this will help to keep outside contaminants outside the system and shut it of with a positive peas on it. IMO

Thanks, I think you just cleared it up for me. I really want the LPC set as low as possible so that when the LLS closes it removes as much refrigerant as possible and still shuts of the compressor.

Am I thinking right?

[K_Neil]

Is there a contactor for the compressor?

[smythers1968]

Is there a contactor for the compressor?

No, Defrost timer

[2sac]

Dumb question. Are you sure the high side cap tube is hooked up to the high side and the low side hooked up to the low side? If the low side cap tube is hooked up to the high side the switch will never open.

[Flip14]

The whole point of a pump down system is to get all the liquid out of the evap and prevent refrigerant migration to the compressor during the off cycle. I usually shoot for around 5psig and set a differential of about 15 to 20 (cut in at 20-25). I don't usually trust the pressure scale on the switch, I don't think they are very accurate. I set it with my what pressure my gages are reading. And if you don't have a contactor that controls the compressor then I would consider putting one on there unless your pressure switches and whatever else is controlling the compressor are rated at 30 amps or better.

[Flip14]

Also you don't want your low pressure cut out below 0psig in case a leak develops on the low side. You would suck air/moisture in the system every time it pumps down.

[joemach]

Also you don't want your low pressure cut out below 0psig in case a leak develops on the low side. You would suck air/moisture in the system every time it pumps down.

You would only suck in air/moisture if there was a leak.

[joemach]

Dumb question. Are you sure the high side cap tube is hooked up to the high side and the low side hooked up to the low side? If the low side cap tube is hooked up to the high side the switch will never open.

This makes the most sense at to what is going on.

Also, it is hard to believe there is no contactor controlling the compressor.

[Flip14]

You would only suck in air/moisture if there was a leak.

Hence the reason I said "in case a leak develops on the low side".

[ZeroTolerance]

Ya, I hope you are not pumping a scroll down to 0PSI Please do yourself a favor and call a pro or for help. If it is a scroll, you could be doing damage to the compressor.

You not having a contactor is another issue. You need to have one!

This thread gets weirder by the second lol