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Old 08-14-2014, 10:23 PM   #1
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warm(ambient temperature) suction line


My HVAC stopped working all of a sudden. Its an R-22 System. The Suction line is warm(ambient temperature) and the liquid line is at the same temperature. The Low side as well as the high side pressure with the compressor off is about 150 psi(manufactured recommended Lo Side Pressure is 150 PSI as well). The compressor draws about 18 amps when the call for heat is made.
What could be the problem? I did not check the pressure on the Hi side with the compressor turned on(Let me know if that will help in understanding the problem and I can measure that).

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Old 08-15-2014, 12:55 AM   #2
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warm(ambient temperature) suction line


Needs to know both Hi side and Low side pressures while compressor is running.

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Old 08-15-2014, 01:48 AM   #3
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warm(ambient temperature) suction line


On turning the compressor on, the suction side pressure quickly drops to 0 and the liquid side pressure goes up to 180 from 150.
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Old 08-15-2014, 04:35 AM   #4
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warm(ambient temperature) suction line


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On turning the compressor on, the suction side pressure quickly drops to 0 and the liquid side pressure goes up to 180 from 150.
Does your system use a TXV? You mentioned heat so I'm assuming heat pump. Could be the reversing valve is not fully switching over. How many seconds does it take to pump down to 0?

If it is a heat pump, what is it doing in cooling mode? There are some sharp posters on this forum that will nail this one pretty easily I think.

Last edited by zappa; 08-15-2014 at 04:51 AM.
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Old 08-15-2014, 05:08 AM   #5
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warm(ambient temperature) suction line


150 is a test pressure, not a recommended pressure for operation.

Since it was around 82 outside when you checked the standing pressure. I'll guess you were running it in cooling mode. You either have a major restriction, or a leak that has caused you to be low on charge.
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Old 08-15-2014, 02:41 PM   #6
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warm(ambient temperature) suction line


Sorry I used the term "call for heat" loosely. What I meant was the thermostat sends the call for hvac to turn on (cooling).

The ambient temperature was around 95 F at the time the pressure was read. The datasheet does say that it has a TXV valve.

Considering the hvac stopped cooling almost overnight what is more likely:

could either be a "major leak"(despite the gauge readings I mentioned?)
or a problem with the TXV
or could the compressor be bad.

Do restrictions have the same symptoms as I am seeing at the moment:
1)equivalised pressure of 150PSI at both Suction and Liquid line when hvac is off.
2)Amp draw of 18 amps(is this too low for a 5Ton HVAC. The RLA on the datasheet says 32.1)
3)Suction line being at ambient temperature(not even slightly cool).
4)The Suction line pressure dropping to 0 while the liquid line pressure climbing to 180 PSI when compressor is on.

Thanks for all the help.
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Old 08-15-2014, 02:55 PM   #7
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warm(ambient temperature) suction line


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4)The Suction line pressure dropping to 0 while the liquid line pressure climbing to 180 PSI when compressor is on.
Clearly you have a blockage, or the expansion valve is not working. But I would also say your charge is low. At 95 degrees your high side should be higher, particularly when there is no flow to the low side.
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Old 08-15-2014, 04:10 PM   #8
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warm(ambient temperature) suction line


Chances are small for TXV issue or blockage. I'll check the refrigerant level first, if it is low (sounds very low), then you have a leak somewhere.
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Old 08-15-2014, 06:06 PM   #9
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warm(ambient temperature) suction line


If the house was warm and its 95 outside. The pressure when the system wasn't running, should have been 181PSIG give or take a couple PSIG. Your reading of 150, indicates its very low on charge.
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Old 08-16-2014, 07:55 AM   #10
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warm(ambient temperature) suction line


if you have a liquid line dryer grab both sides of the piping if you feel a cooler line heading to the house then the other might may have a restriction...that 150 standing pressure tells you the Freon is still within the system.what is the RLA on the condenser tag for the compressor 18 seems high just read the compressor not the disconnect or substract the condenser fan rating amps?
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Old 08-16-2014, 11:36 AM   #11
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warm(ambient temperature) suction line


Quote:
Originally Posted by jaywalker1981 View Post
Do restrictions have the same symptoms as I am seeing at the moment:
1)equivalised pressure of 150PSI at both Suction and Liquid line when hvac is off.
2)Amp draw of 18 amps(is this too low for a 5Ton HVAC. The RLA on the datasheet says 32.1)
3)Suction line being at ambient temperature(not even slightly cool).
4)The Suction line pressure dropping to 0 while the liquid line pressure climbing to 180 PSI when compressor is on.

Thanks for all the help.
1) Equalized pressures are normal. A few minutes after shutting down the HP and LP become the same as the refrigerant passes through a designed restriction (fixed orifice or TXV valve).

2) Your amp draw is low for a restriction and 95* outdoor temp and warm house.

3) Restriction or low charge.

4) Suction line dropping to 0 is a classic sign of a restriction but liquid line should be much higher than 180 if you had a proper charge.

With your additional information I'm leaning towards a very low charge. The only fly in the ointment is how fast this occurred. Try another static pressure test and see if it has dropped even lower. Listen at the TXV location for odd noises like a combination of liquid and vapor being forced through a small hole. It is supposed to be liquid only at this location.

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