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  #1  
Old 3/16/10, 1:06 AM
George F. Fransway George F. Fransway is offline
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Default HVAC testing at 60 Degrees F

During an inspection today, I used the thermostat to start the A/C for a few minutes at 60 Degrees F. I do this to see if the compressor fires, not to test the temperature differential. After a minute or two, the circuit breaker tripped off, it is my understanding of A/C principals that the compressor should not be run for a long time at low temperatures and that a short test like this will not run HIGH amps and should not trip the breaker? Any input from a A/C guru?
Thanks George
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  #2  
Old 3/16/10, 1:28 AM
Buck Hartley, CMI's Avatar
Buck Hartley, CMI Buck Hartley, CMI is offline
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Default Re: HVAC testing at 60 Degrees F

I am not a AC guru. That should not happen. Defer the system to a
HVAC contractor.



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  #3  
Old 3/16/10, 2:05 AM
George F. Fransway George F. Fransway is offline
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Default Re: HVAC testing at 60 Degrees F

Thanks
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  #4  
Old 3/16/10, 10:42 AM
Jeffrey R. Pope, CMI's Avatar
Jeffrey R. Pope, CMI Jeffrey R. Pope, CMI is offline
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Default Re: HVAC testing at 60 Degrees F

A tripping breaker is an indication of a failing compressor. . .



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  #5  
Old 3/16/10, 12:06 PM
David A. Andersen, TN HI# 40's Avatar
David A. Andersen, TN HI# 40 David A. Andersen, TN HI# 40 is offline
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Default Re: HVAC testing at 60 Degrees F

Put a little oil and liquid refrigerant on top of that compressor piston and watch the amperage go up!

Do you know what a low ambient control is?

You may have locked up the compressor. Locked rotor average tends to trip circuit breakers.

Anyone testing air conditioning under low ambient conditions, I highly recommend that you do it from outside the house, not at the thermostat.

You can turn the circuit breaker off when you hear the compressor about to jump out of the condensing unit.



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Bracebridge, Ontario:


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Old 3/16/10, 1:16 PM
Brian A. MacNeish Brian A. MacNeish is offline
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Default Re: HVAC testing at 60 Degrees F

Quote:
Originally Posted by dandersen View Post
(1) Put a little oil and liquid refrigerant on top of that compressor piston and watch the amperage go up!

Do you know what a low ambient control is?

You may have locked up the compressor. Locked rotor average tends to trip circuit breakers. (Locked rotor amperage tends to trip circuit breakers.)

Anyone testing air conditioning under low ambient conditions, I highly recommend that you do it from outside the house, not at the thermostat.

You can turn the circuit breaker off when you hear the compressor about to jump out of the condensing unit.
(1) Shouldn't the accumulator catch this if the unit is only run momentarily?
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  #7  
Old 3/16/10, 4:30 PM
Gary Reecher Gary Reecher is offline
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Default Re: HVAC testing at 60 Degrees F

The compressor crankcase heater may have failed and the refrigerant migrated to the compressor oil. Start up under that condition could lead to compressor pulling in foaming oil and locking up.
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  #8  
Old 3/16/10, 4:51 PM
David A. Andersen, TN HI# 40's Avatar
David A. Andersen, TN HI# 40 David A. Andersen, TN HI# 40 is offline
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Default Re: HVAC testing at 60 Degrees F

Not many a/c units have a crankcase heater!

It costs too much!

Only Heat Pumps do.



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  #9  
Old 3/16/10, 5:13 PM
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Brian K. Smith Brian K. Smith is offline
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Default Re: HVAC testing at 60 Degrees F

my question why even take the chance?
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  #10  
Old 3/19/10, 1:23 AM
George F. Fransway George F. Fransway is offline
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Default Re: HVAC testing at 60 Degrees F

good input thanks to all. george
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  #11  
Old 3/19/10, 1:33 AM
Doug Edwards Doug Edwards is offline
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Default Re: HVAC testing at 60 Degrees F

Quote:
Originally Posted by Brian A. MacNeish View Post
(1) Shouldn't the accumulator catch this if the unit is only run momentarily?
He didn't say it was a Heat pump. He said it was an HVAC which leads me to believe it was a standard air conditioner which does not have an accumulator (heat pumps do).





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  #12  
Old 3/19/10, 6:59 AM
Brian A. MacNeish Brian A. MacNeish is offline
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Default Re: HVAC testing at 60 Degrees F

Quote:
Originally Posted by dedwards View Post
He didn't say it was a Heat pump. He said it was an HVAC which leads me to believe it was a standard air conditioner which does not have an accumulator (heat pumps do).
I live in a cool/cold climate. Just about everything I see up here is HP/AC.
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  #13  
Old 3/19/10, 2:13 PM
C. Scott Justason's Avatar
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Default Re: HVAC testing at 60 Degrees F

Quote:
Originally Posted by dandersen View Post
Put a little oil and liquid refrigerant on top of that compressor piston and watch the amperage go up!

Do you know what a low ambient control is?

You may have locked up the compressor. Locked rotor average tends to trip circuit breakers.

Anyone testing air conditioning under low ambient conditions, I highly recommend that you do it from outside the house, not at the thermostat.

You can turn the circuit breaker off when you hear the compressor about to jump out of the condensing unit.
60 degrees is not a low ambient condition. I don't care where your from.
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  #14  
Old 3/19/10, 3:06 PM
David A. Andersen, TN HI# 40's Avatar
David A. Andersen, TN HI# 40 David A. Andersen, TN HI# 40 is offline
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Default Re: HVAC testing at 60 Degrees F

Somebody thinks so.

What's your point?

Please enlighten me as to what a low ambient condition actually is...

I happen to be from the South (at this point in my life) and it gets down to about 21° at night and up to 60 during the day.
Do you think this is okey-dokey to run an air conditioner at 10 o'clock in the morning when it reaches 60?

70 psig is the design operating temperature for R-22 refrigerant.

What's the saturation temperature at this pressure at atmospheric conditions at sea level?

Now please enlighten us as to what the saturation pressure is at 32°F for R-22 refrigerant.

What's the pressure difference?

Does a freezing evaporator coil not potentially cause refrigeration slugging?

At what outdoor temperature does refrigeration pressures on the high side fall to a point where the back pressure falls below the freezing temperature? Don't tell me it depends on the equipment.

Is it just slightly possible that cool outdoor air and no load in the house may cause a "low ambient condition"?

Please keep in mind that no one here is required to be certified to put a set of refrigeration gauges on an air-conditioning unit.
Please explain how everyone here will know when a low ambient condition exists without installing a set of refrigeration gauges!?



"working together to get-IR-done" Chris Walsh
Bracebridge, Ontario:


David A. Andersen & Associates
Clarksville - Nashville Home Inspector Lic#40
http://www.midtninspections.com
ITC Level III Thermographer Cert#1958
Building Science Thermographer Cert#33784
http://www.thermalimagingscan.com
HVAC Certification EPA Cert#2046620
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Link to my Website at: http://www.midtninspections.com/link-submission

Last edited by dandersen; 3/19/10 at 3:19 PM..
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  #15  
Old 3/19/10, 7:23 PM
Mark Nahrgang, C.R.I.'s Avatar
Mark Nahrgang, C.R.I. Mark Nahrgang, C.R.I. is offline
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Default Re: HVAC testing at 60 Degrees F

Quote:
2.5. Cooling
I. The inspector shall inspect:
A. the central cooling equipment using normal operating controls.
II. The inspector is not required to:
A. determine the uniformity, temperature, flow, balance, distribution, size, capacity, BTU, or supply adequacy of the cooling system.
B. inspect window units, through-wall units, or electronic air filters.
C. operate equipment or systems if exterior temperature is below 60 degrees Fahrenheit, or when other circumstances are not conducive to safe operation, or may damage the equipment.
D. inspect or determine thermostat calibration, cooling anticipation, or automatic setbacks or clocks.
E. examine electrical current, coolant fluids or gases, or coolant leakage.
60 degrees is fine. My personal rule of thumb is 65 just to be on the safe side, but I've been known to fudge on that for a degree or two. Most of the AC operator manual I've seen actually list values less than either (down in the 50-55 range).

The breaker tripped because of a system problem, not an inspection problem.



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Home Inspections for Springfield, Dayton, and surrounding OH areas.
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