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Old 09-23-2009, 03:03 PM   #1
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I think something is wrong...


In cooling mode I have a 2 degree superheat but pressures look OK. Tested the TXV with ice water and superheat didn't change or pressures for that matter. Put the system in heat mode and the supply temperature was erratic, reaching 100 degree and dropping 10 degrees in 5 seconds, back up to 103 then dropping again. Does this sound like a TXV gone bad??

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Old 09-23-2009, 05:21 PM   #2
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I think something is wrong...


yep....

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Old 09-23-2009, 06:39 PM   #3
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I think something is wrong...


Quote:
Originally Posted by carlb7 View Post
In cooling mode I have a 2 degree superheat but pressures look OK. Tested the TXV with ice water and superheat didn't change or pressures for that matter. Put the system in heat mode and the supply temperature was erratic, reaching 100 degree and dropping 10 degrees in 5 seconds, back up to 103 then dropping again. Does this sound like a TXV gone bad??
Sounds like the TXV is hunting. Time for a new one
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Old 09-23-2009, 07:26 PM   #4
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I think something is wrong...


2 deg. of superheat? Bad TXV?

What type of refrigerant?
What is suction pressure and temp?
What is liquid line pressure and temp?
What is temp differance at A/H?
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Old 09-23-2009, 09:11 PM   #5
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I think something is wrong...


Refrigerant in R22.
The TXV bulb was taken off the line and the cabinet was closed back up with the bulb on the outside dangling. It was a 70 degree mild day. Here were the readings.
High Pressure=165
Low Pressure=65
Suction Temp=41
Liquid Line=79

Then the bulb was submerged into ice water. After about 5 minutes here were the readings.
High Pressure=175
Low Pressure=66
Suction Temp=42
Liquid Line=79

One other observation. When you put your ear up to the liquid line you can here a change in the sound of the refrigerant flow when the bulb was submerged into the ice water.
I then put it into heat mode and got the erratic temperatures. The outside condenser has a fixed orifice and in heat mode that is the metering device and yet the TXV still seems to have an affect. I guess thats normal.
I think newtech and hvaclover may be correct.
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Old 09-23-2009, 09:38 PM   #6
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I think something is wrong...


Numbers don't make sense. Hows the air flow?
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Old 09-23-2009, 10:20 PM   #7
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I think something is wrong...


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Originally Posted by hvaclover View Post
Numbers don't make sense. Hows the air flow?
41 deg suction line, not enough air through evaporator coil.

Plugged air filter, plugged evaporator coil, blower not getting to speed, air by-passing evaporator coil or grills blocked or closed are just some of the issues to look for.

The TXV is as closed as it can get already with this suction line temp, so ice won't make a differance.

Compressor is pumping liquid (they don't like to do this)
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Old 09-23-2009, 10:31 PM   #8
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Quote:
Originally Posted by KAVF View Post
41 deg suction line, not enough air through evaporator coil.

Plugged air filter, plugged evaporator coil, blower not getting to speed, air by-passing evaporator coil or grills blocked or closed are just some of the issues to look for.

The TXV is as closed as it can get already with this suction line temp, so ice won't make a differance.

Compressor is pumping liquid (they don't like to do this)

KAVF, I dont't disconnect bulbs from the txv cause the sheet metal practices here make it almost impossible to get at.

What does that 41 degrees tell you exactly.
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Old 09-23-2009, 10:40 PM   #9
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I think something is wrong...


41 deg tells me that the evaporator coil is getting too cold. Not enough heat (air) being absorbed. I don't have an indoor entering temp, but asuming it is at least 70 deg. if it is suction line temp should be around 52 to 57 deg with proper airflow.
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Old 09-23-2009, 10:47 PM   #10
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The evaperator coil was replaced last winter should still be fairly clean.. Blower motor seems to be working at normal speed. All filters have been replaced. The return has a 20x12 duct plenum and there is a filter grill below the upflow that is 14x14 as well. It is a zoned system with all zones open during testing. Is there any other reason for these readings??
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Old 09-23-2009, 10:53 PM   #11
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On the zone system is there a dump damper that dumps excess air into the return duct?

What is the air temp of house and air temp entering unit through return at the unit?
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Old 09-23-2009, 10:58 PM   #12
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Quote:
Originally Posted by KAVF View Post
41 deg tells me that the evaporator coil is getting too cold. Not enough heat (air) being absorbed. I don't have an indoor entering temp, but asuming it is at least 70 deg. if it is suction line temp should be around 52 to 57 deg with proper airflow.
Yeah but that was with the bulb disconnected.
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Old 09-23-2009, 11:06 PM   #13
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I think something is wrong...


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Refrigerant in R22.
The TXV bulb was taken off the line and the cabinet was closed back up with the bulb on the outside dangling. It was a 70 degree mild day. Here were the readings.
High Pressure=165
Low Pressure=65
Suction Temp=41
Liquid Line=79


What are these reading with the bulb connected?
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Old 09-23-2009, 11:16 PM   #14
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I think something is wrong...


Quote:
Originally Posted by KAVF View Post
carlb7
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Refrigerant in R22.
The TXV bulb was taken off the line and the cabinet was closed back up with the bulb on the outside dangling. It was a 70 degree mild day. Here were the readings.
High Pressure=165
Low Pressure=65
Suction Temp=41
Liquid Line=79


What are these reading with the bulb connected?
No. They are with the bulb detached.
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Old 09-23-2009, 11:23 PM   #15
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I think something is wrong...


Yes. those readings are with the bulb detached. I will give readings tomorrow with bulb reattached. There is a bypass duct but with all the zones calling the duct is closed. I appreciate all of your help. Tomorrow I will get readings with bulb attached and post them here. The erratic temperatures when it was in heat mode were taken with the bulb reattached.

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