Weak cooling


  #1  
Old 10-03-05, 05:20 PM
rfmw
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Weak cooling

Hi,

I have a Carrier split unit (circa 1994) in North Texas that was running very strongly until about a week ago. Unit has a scroll compressor in condensor unit.

Suddenly, I noticed that it was not keeping up with the heat load inside the house.

-The air filter is of good quality, clean and new (<1 month old).
-When I start it up with indoor temp at 82 degF and outdoor at ~90 degF, and let it run for 10-20 mins, the low-side pressure is 100 psig, while the high-side pressure is 200 psig.
-High-side line at condensor unit is just barely warm, and low-side just barely cool (and no sweat).
-A spot-check of the evaporator coil shows that it is just barely cool and is not sweating (and no water at all on floor of plenum under it).
-The volume of air flow seems as high as it always has been, and there is no icing whatsoever on the evaporator coil.
-There are no visible bubbles or excessive corrosion on the edges of the coil.
-There is no, and never was, a filter-dryer on the high side line.

One analysis I have been able to find for high suction-side pressure is "an obstruction in the line", as this design does not have an expansion valve (has capillary tubes).

One tech wants to sell me a new evaporator coil, and another thinks that is not the problem.

Any ideas from you all here?

Thanks.
 
  #2  
Old 10-04-05, 05:15 AM
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You very well could have 100psi with 82 house. Did you use a liscensed Carrier dealer to look at it ??

The refrigeration circuit is not a DIY project and is best left to a trustworth pro.
 
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Old 10-06-05, 09:55 AM
rfmw
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Need more info

Thanks for the response. What I am trying to do is understand the situation so I can tell if people that come here to look at it are shooting straight with me.

I noted that inside the plenum where the evaporator coil is located, on the liquid line, there is a threaded interconnect right before the split to the capillary tubes.

This interconnect is just 12 inches from the sweated interconnect on the outside of the plenum, making me think that there is something else going on there. I'm suspecting that there is a servicable strainer inside of it (this system appears to have no filter/dryer on it anywhere that I can find).

Could this be true? I'm having another tech over in about 2-3 hours from now and I want to see if he picks up on this and tries to inspect it, or if he tries to sell me a new evaporator coil as well.

Thanks for any help.
 
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Old 10-06-05, 11:56 AM
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There could be a restriction in the piston where you're reffering but it's only servicable if the refrigerant is recovered.

There may be a liquid line drier located inside the condensor unit outside from the factory.
 
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Old 10-06-05, 12:10 PM
rfmw
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Strainer?

Don't worry; I'm not going to service it myself. It's obvious that I do not have the proper equipment or certification to break open the refrigeration circuit here. Please don't keep drilling me about how this is not a DIY project. I understand. I am trying to audit the diagnoses of techs that look at my system so I can (attempt to) mitigate getting ripped off.

All I am asking is has anyone seen this arrangment and why is that threaded interconnect there? It seems like an unnecessary leak opportunity unless it is there for servicability.

The condensor has a scroll compressor (no piston) and I do not believe that there is a filter/dryer anywhere on the liquid line, except maybe here (if this is in fact a filter or strainer).
 
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Old 10-06-05, 12:51 PM
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That threaded device is where the piston would be located. I'm sorry to have led you to think I was drilling you, but the piston I'm reffering to is not the type that's in a recip compressor. It's a type of metering device for the refrigerant entering the evaporator and that's probably why you can here the refrigerant flow. With a txv it's much quieter and you don't hear the refrigerant flow.
 
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Old 10-06-05, 12:59 PM
rfmw
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Thanks

Sorry that I misunderstood about the piston.

So you're saying that you believe that the threaded interconnect is a provision for an optional expansion valve, and currently there is none installed.
 
  #8  
Old 10-07-05, 08:32 PM
J
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Your low side pressure is too high. Possibilities are, metering device not working (wide open) or compressor problem.
 
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Old 10-08-05, 12:05 PM
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Jim did mention a compressor problem which is a valid point. If the valves are leaking through it will cause this also.

Also how does your return air duct look?? It's not open anywhere in a attic or crawl space pulling hot air in is it??

By the way. Welcome to the forum Jim.
 
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Old 10-08-05, 12:11 PM
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Besides. Now that my brain fart has cleared, a restriction in the piston or cap tubes would cause high head and low suction.
 
 

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