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Old 06-02-2009, 08:20 PM   #1
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AC guy came out and said..


So it's that time of year to start using the AC. Unfortunately my AC is putting out 6-7F temperature difference between the return and supply. I moved into the house in December and don't know the history of the HVAC system. The house was a foreclosure and according to the neighbors was a rental, so the owners probably didn't take very good care of it.

AC guy came out for a diagnosis. Return temp about 76, 60% humidity. Supply temp about 70. Outside temperature 84, 30-40% humidity. Suction line was showing 100 psi, 60F, high pressure line was reading about 170 psi. This is a 3 Ton Payne unit. There is no nameplate on the condenser, service guy said it was installed in 97 from the serial number on the evaporator coil housing.

The service tech said the system was overcharged and proceeded to bleed out the refrigerant into the atmosphere for what seemed like several minutes (isn't R22 not that great for the environment?). The suction line pressure didn't drop a bit. The high pressure line didn't seem to drop either but I don't remember exactly what it read in the beginning. He diagnosed a bad compressor. Does this sound right? Could it be anything else?

If it is indeed a bad compressor, I don't think it's worth replacing, and will probably get a whole new system. Unfortunately the house could also use a new roof and I can't do both right now. Homeownership sucks.

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Old 06-02-2009, 10:13 PM   #2
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AC guy came out and said..


Sure could be a bad compresser. And replacing a 12 year old unit won't hurt your electric bill at all.

What part ok the country do you live in?

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Old 06-03-2009, 05:53 PM   #3
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AC guy came out and said..


Bad compressor sounds like defective valves. Replace system with High EEF unit.
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Old 06-03-2009, 06:29 PM   #4
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AC guy came out and said..


Valves in the compressor are worn out/not seating and pumping properly. Usually you get a 4:1 compression ratio, ie: 50 psig low and 200 discharge or a similar proportion on a healthy compressor. I would buy a new system. Don't buy it from that guy, he is clueless.
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Old 06-03-2009, 06:30 PM   #5
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AC guy came out and said..


I wouldn't rule the compressor bad yet.

To see if the compressor is trash have the tech hook up gauges, close the high side service valve on the condenser and then hold the contactor in and watch the gauges and see if the gauges can go to zero. This may take 3-4 mins

What you are doing is taking the freon in the system and storing it into the condensing coils. If the gauges go to zero then the valves are working and more than likely it is just over charged. If the gauges won't go to zero the the valves are trash.

If the gauges zero then have the tech recover the system and pull a vaccum on the system and then weigh in the freon.
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Old 06-03-2009, 06:35 PM   #6
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AC guy came out and said..


In my experience if it is overcharged it runs higher than normal high pressure (bottom of condensor fills up, reducing its capacity) AND causes the suction line to the compressor to ice up/slug liquid to the compressor.
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Old 06-03-2009, 07:16 PM   #7
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AC guy came out and said..


Sound like a bad compressor if there was no change in the pressure after venting the gas. Could be an extremely plugged condenser but I doubt it.
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Old 06-04-2009, 07:34 AM   #8
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AC guy came out and said..


Agree with yuri and hvaclover bad compressor.

Don't throw good money into bad system.
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Old 06-04-2009, 09:56 AM   #9
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AC guy came out and said..


Thanks for all the replies.

Theoretically.... if the exansion valve was way too big, could that explain why the compressor is only compressing 1.7 times. If there's very little restriction in the system, the compressor would just be pumping the refrigerant, but there would not be a lot of pressure difference between the suction and discharge lines.

I do want to do the test Plumber101 suggested. I'm assuming there's some sort of safety device build into the compressor so it can't overpressurize/blow up the condenser coil. Pressure relief, pressut switch cutoff? I'd like to do this myself without any techs, are the standard fittings 1/4" SAE 45degree flare?

If it's indeed a bad compressor, I will surely get a whole new system. Does the price vary much/at all if I get it installed in the summer months vs winter? The house is in the shade, so even on 90 degree days it doesn't get above 78 inside, maybe, just maybe I can live with the old unit for a little bit.
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Old 06-04-2009, 12:16 PM   #10
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AC guy came out and said..


Quote:
Originally Posted by peterk View Post
Thanks for all the replies.

Theoretically.... if the exansion valve was way too big, could that explain why the compressor is only compressing 1.7 times. If there's very little restriction in the system, the compressor would just be pumping the refrigerant, but there would not be a lot of pressure difference between the suction and discharge lines.

I do want to do the test Plumber101 suggested. I'm assuming there's some sort of safety device build into the compressor so it can't overpressurize/blow up the condenser coil. Pressure relief, pressut switch cutoff? I'd like to do this myself without any techs, are the standard fittings 1/4" SAE 45degree flare?

If it's indeed a bad compressor, I will surely get a whole new system. Does the price vary much/at all if I get it installed in the summer months vs winter? The house is in the shade, so even on 90 degree days it doesn't get above 78 inside, maybe, just maybe I can live with the old unit for a little bit.
If we are to give you full and accurate information and you know the type of expansion valve it has it necessary for you to inform us.

But if you are referring to a simple fixed orifice being over sized than I would disagree.

A TXV stuck completely open would be true to your description but I Don't see that being the case because it is Payne equip and a ten SEER unit.
All that and the fact that it is a rental makes me think other wise.

With respect to Plumber101, that is not a true test of the valve integrity.

I can pump a compressor down to 20"hg that has bad valves.

Plumber101 also failed to mention that if the valves are bad the freon pressure would start to equalize, leaking back thru the high side into the low side.
That is the acid test.
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Old 06-04-2009, 01:46 PM   #11
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AC guy came out and said..


Quote:
Originally Posted by hvaclover View Post
If we are to give you full and accurate information and you know the type of expansion valve it has it necessary for you to inform us.

But if you are referring to a simple fixed orifice being over sized than I would disagree.

A TXV stuck completely open would be true to your description but I Don't see that being the case because it is Payne equip and a ten SEER unit.
All that and the fact that it is a rental makes me think other wise.

With respect to Plumber101, that is not a true test of the valve integrity.

I can pump a compressor down to 20"hg that has bad valves.

Plumber101 also failed to mention that if the valves are bad the freon pressure would start to equalize, leaking back thru the high side into the low side.
That is the acid test.
I agree with hvaclover and another thing is you seem to know quite about the system being a diyer, how do you know the TXV is over-sized???? and you should think twice regarding shutting off the liquid valve as a diyer you could be creating a hand grenade, do you have gages and know how to use them???? Is there a HPCO on the unit???? Plumber 101 should not be advising people to close that valve it's not a refrigeration system with a receiver for pump down operation. Be Careful.
PS. BAD COMPRESSOR

Last edited by SULTINI; 06-04-2009 at 01:48 PM. Reason: Sorry plumber 101 you advised him to get the tech to check it.
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Old 06-04-2009, 04:46 PM   #12
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AC guy came out and said..


That compressor is bad. Suction is high and head is low, valves aren't holding. Unless someone mixed the refrigerant.

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