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Old 08-17-2011, 07:39 AM   #1
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Has anyone ever heard of using a solenoid valve on the high side as a control? The guy had a very thick chinese accent so it was hard to understand him, but what I could gather was before they would use a low pressure switch instead of a thermostat? But now they use a solenoid valve instead... please help me make sense of this?
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Old 08-17-2011, 07:45 AM   #2
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Thermostat reaches set point and closes LLS the unit pumps down and the low pressure control shuts the compressor off.

Thermostat calls for cooling the reverse happens. LLS opens and the LP switch makes and starts the compressor.
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Old 08-17-2011, 07:54 AM   #3
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Ok so the low pressure switch is wired in series with the compressor... from my understanding the solenoid valve merely opens and closes the refrigerant line when voltage is applied (in this case 120v). Why is that a necessarry component? This is not a huge walk in cooler, maybe 1010
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Old 08-17-2011, 12:59 PM   #4
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I would recommend you buy or get from a library a textbook called "Fundamentals of Refrigeration" and learn about the refrigeration cycle. They pump down units because freon and oil migrate to the coldest area/evaporator in the off cycle and the compressor needs oil on startup. On a resi AC units the condensor is physically large enough to hold all the refrigerant but on a walk in the condensor is very small and all the refrig needs to be stored in the receiver during the off cycle so it gets pumped there by the pump down process. Lots of this is basic refrigeration which most techs should take an interest in as it applies to both AC and refrigeration.
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Old 08-17-2011, 02:02 PM   #5
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I would recommend you buy or get from a library a textbook called "Fundamentals of Refrigeration" and learn about the refrigeration cycle. They pump down units because freon and oil migrate to the coldest area/evaporator in the off cycle and the compressor needs oil on startup. On a resi AC units the condensor is physically large enough to hold all the refrigerant but on a walk in the condensor is very small and all the refrig needs to be stored in the receiver during the off cycle so it gets pumped there by the pump down process. Lots of this is basic refrigeration which most techs should take an interest in as it applies to both AC and refrigeration.
Ya Mon Good explaination to the guy.
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Old 08-18-2011, 12:17 AM   #6
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Lol I learned about this "pump down" deal today. The guys at Grangers are awesome. I know the refrigeration cycle. I went to trade school and been doing residential hvac for a little over 5 years. But this was kind of a puzzle. The air handeler was bare. I had to install the txv, which was fine. But when I saw the solenoid I was wondering how that fit in... and there was no thermostat, which was the missing puzzle piece. I went and got the thermostat and realized there was no low voltage going to the condenser.... hmm, well I guess that's what that low pressure control is for haha. I thought this was going to be like a ductless mini split, but even the valves are different. There are no schraeders??!! Why not??!!
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Old 08-18-2011, 04:31 AM   #7
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Because they are King valves. Fully back seated, the service port is closed off, and the valve is open from the evap side to the compressor. Fully front seated, the evap side is closed off from the compressor, and the service port is open to the compressor side of the valve. Front seated 1 turn, the service port is open. And that is when/how you check system operation, recover, or ad charge.

Use a refrigeration service wrench on it, not an adjustable.
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Old 08-18-2011, 06:08 AM   #8
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Lol I learned about this "pump down" deal today. The guys at Grangers are awesome. I know the refrigeration cycle. I went to trade school and been doing residential hvac for a little over 5 years. But this was kind of a puzzle. The air handeler was bare. I had to install the txv, which was fine. But when I saw the solenoid I was wondering how that fit in... and there was no thermostat, which was the missing puzzle piece. I went and got the thermostat and realized there was no low voltage going to the condenser.... hmm, well I guess that's what that low pressure control is for haha. I thought this was going to be like a ductless mini split, but even the valves are different. There are no schraeders??!! Why not??!!
There are millions of small commercial refrigeration systems out there that have nothing but a low pressure control that keeps the temps in the box, IE small bain Marie's, beer coolers, deli cases. The pressure switch is the thermostat. Cut in and cut out pressure. Temperature/pressure relationship.
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Old 08-18-2011, 06:50 AM   #9
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the setting depend on the refrig being used but the controlling of the unit is typical on small refer units...reference this chart for productpsi/temp ranges
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Old 08-18-2011, 11:16 AM   #10
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There are millions of small commercial refrigeration systems out there that have nothing but a low pressure control that keeps the temps in the box, IE small bain Marie's, beer coolers, deli cases. The pressure switch is the thermostat. Cut in and cut out pressure. Temperature/pressure relationship.
I thought so but in that application how would a solenoid valve play into the equation?
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Old 08-18-2011, 11:18 AM   #11
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Because they are King valves. Fully back seated, the service port is closed off, and the valve is open from the evap side to the compressor. Fully front seated, the evap side is closed off from the compressor, and the service port is open to the compressor side of the valve. Front seated 1 turn, the service port is open. And that is when/how you check system operation, recover, or ad charge.

Use a refrigeration service wrench on it, not an adjustable.
Its the same wrench for a regular condensing unit... my question is why don't they make the valves the same as a king valve on a condensing unit? Is there some special reason for the difference?
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Old 08-18-2011, 02:25 PM   #12
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Yours was a different application I was just giving you more information on the various ways to control a refrigeration system. Yuri's explanation was great reread that.
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Old 08-18-2011, 07:41 PM   #13
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Its the same wrench for a regular condensing unit... my question is why don't they make the valves the same as a king valve on a condensing unit? Is there some special reason for the difference?

On some Carrier units they do use King valves. Its mostly a money issue. A king valve cost more.
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