Ruud Heat Pump

 
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Old 11-27-2010, 05:28 PM   #1
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Ruud Heat Pump


I recently went to service a Ruud Heat Pump & encountered a problem that I haven't seen in 30 years in the trade. Cooling cycle is spot on, in Heating cycle the pressures are at first low, the low side @ 10-15 PSI & highside hovering @ 250 PSI. After awhile, the high side will climb to 450+ & trip the pressure switch. The unit has an ouside TXV & a Charge Compensator. Any other brand I would replace the TXV.

I've never heard of a Charge Compensator in all of my training. Never been to Rheem/Ruud school but have worked on many without encountering a Charge Compensator.

Locally, Ruud is out of the market & have no one readily available to advise or refer to a factory tech. The Rheem distibutor won't even discuss Ruud.

What is a Charge Compensator & how does it work?
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Old 11-27-2010, 07:17 PM   #2
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Re: Ruud Heat Pump


It holds the extra refrigerant in heating mode. that the unit needed in cooling mode.

As the direction of refrigerant flow changes. So does the type of refrigerant that enters the compensator. In one direction, liquid goes into it. In the other direction, hot gas flows into it.

Several manufacturers have used them on various models over the years. Rheem, York, Lennox come to mind.

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Old 11-30-2010, 08:37 PM   #3
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Re: Ruud Heat Pump


It sounds to me like the condensor txv is smack open. I know they have accumulators in them but that hardly stores much freon. It's sole purpose is to prevent liquid from getting to the compressor and it's on the dedicated suction line so no matter witch mode ur in shouldn't make a difference. I'd like to know the cooling pressures. The evap coil could be to small or the evap txv no good allowing the mistake of the system being over charged to begin with.
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Old 12-01-2010, 05:22 AM   #4
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Re: Ruud Heat Pump


Quote:
Originally Posted by Harlemnt View Post
It sounds to me like the condensor txv is smack open. I know they have accumulators in them but that hardly stores much freon. It's sole purpose is to prevent liquid from getting to the compressor and it's on the dedicated suction line so no matter witch mode ur in shouldn't make a difference. I'd like to know the cooling pressures. The evap coil could be to small or the evap txv no good allowing the mistake of the system being over charged to begin with.
Lots of manufacturers have used them over the years. Its not something that you just add to a system in the field.
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Old 12-01-2010, 10:26 AM   #5
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Re: Ruud Heat Pump


Quote:
Originally Posted by Harlemnt View Post
It sounds to me like the condensor txv is smack open. I know they have accumulators in them but that hardly stores much freon. It's sole purpose is to prevent liquid from getting to the compressor and it's on the dedicated suction line so no matter witch mode ur in shouldn't make a difference. I'd like to know the cooling pressures. The evap coil could be to small or the evap txv no good allowing the mistake of the system being over charged to begin with.

It’s not really the same as a suction accumulator though, since the excess "liquid" refrigerant condenses there when the suction line is cool. When the suction line is carrying hot gas, it evaporates the refrigerant returning it to the system.

This is how Parker describes it:
A compensator tank is a mode dependent receiver that can be used in a heat pump system. As the heating mode does not require as much refrigerant as the cooling mode, the compensator tank stores the excess refrigerant.

Last edited by DuMass; 12-01-2010 at 02:05 PM. Reason: improve description
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Old 12-03-2010, 06:12 AM   #6
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Re: Ruud Heat Pump


Isn't the accumulator always on suction side? Reversing valve changes the coils, but accumulator should remain on the low side. I believe it is just a can with a U trap inside. One end connects directly to the compressor intake and the other end sits mid-air in the can. Refrigerant leaving the evaporator as liquid will drop to the bottom of the can while vapor freely returns to compressor.

The concept is simply using a reversing valve to swap the role of indoor and outdoor coils, but in actual application, additional controls are necessary to accommodate operating temperature range.

The bottom of U has a pin hole so the refrigerant gas flowing through it will create a reduced pressure(venturi effect) so the non-volatile oil doesn't keep piling up in the accumulator.

Accumulators are very common in refrigeration.

A heat pump operates in conditions very similar to a refrigerator. Evaporator temperature ranges from what you expect inside a fridge and a freezer and pumps heat into "room temperature".

It's low/medium back pressure in heat mode and high back pressure in cool mode. Straight cool units usually don't have accum. but some reverse-cycle (heat pumps) do.

When you compare the same tonnage & SEER Rheem package units between straight cool and heat pump models, the heat pump version contains significantly more refrigerant.

Last edited by Electric_Light; 12-03-2010 at 06:15 AM.
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Old 12-03-2010, 09:01 AM   #7
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Re: Ruud Heat Pump


The charge compensator is not so much an accumulator, but is actually a low side receiver.
It’s usually connected to the "suction" line on other side of the reversing valve coming from the outdoor coil. The temperature change of the line during cooling and heating mode is what causes the refrigerant to collect in or leave the compensator.

Here is a link I found for a Lennox unit that shows a compensator in the suction line coming from the outdoor coil. The diagram is on page 4.
http://www.hvacpartsshop.com/HP25%20Series.pdf


Here is a good description from Bristol Compressor:

The use of a charge compensator (low side receiver model PR 3083 manufactured by Parker Hannifin) in heat pump applications is another way of controlling refrigerant. This receiver mounts in the suction line coming from the outdoor coil to the reversing valve. Do not get this line confused with the common suction line from the reversing valve to the compressor where an accumulator is normally installed. During the heating mode, refrigerant is pulled into the receiver/compensator due to the low temperature of the suction line going through the device.
During the heating mode, there can be a large percentage of the refrigerant charge backed up in the condenser (indoor coil in the heating mode). This backed up refrigerant can cause an increase in discharge pressure and a loss of heat output from the system. By storing this excess refrigerant in the low side receiver, the system would have better control of the refrigerant and the system efficiency would increase due to operating at a reduced high side pressure. Liquid return to the compressor during defrost could also be reduced, possibly eliminating the need for an accumulator.
Prior to eliminating the accumulator, extensive system testing would be required to confirm all liquid surges (especially during defrost termination) have been reduced to a level that will not endanger the compressor.

Last edited by DuMass; 12-03-2010 at 11:16 AM. Reason: add link and description
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Old 12-03-2010, 02:50 PM   #8
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Re: Ruud Heat Pump


Here is some more detailed information on the compensator.
Attached Files
File Type: pdf Refrigerant Charge Compensators.pdf (145.5 KB, 1432 views)
File Type: pdf Refrigerant Charge Compensator 2.pdf (115.2 KB, 284 views)

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