What makes compressors fail

[hvacbear]

Bornriding and shophound read my mind and robo filled in any voids. Other than their reasons I have seen a few compressors fail due to improper 3phase power. For no apparent reason a comp failed and the voltaged were something like 221/222/174 we made a big fiasco and the electricians came in to swap some loads around and do a reassesment.

[comfortmaster1]

Originally posted by geoexchangeman
What is the number one cause for compressor failure.

When they don't study for their test.

What's up with all the credentials?

[docholiday]

What makes compressors fail ?

One Word....







Stress.

Take your pick, Thermal Stress, Electrical Stress, Mechanical Stress, and Chemical Stress.

As Shophound said, they are murdered.

[schmuck]

Originally posted by docholiday
What makes compressors fail ?

One Word....







Stress.

Take your pick, Thermal Stress, Electrical Stress, Mechanical Stress, and Chemical Stress.

As Shophound said, they are murdered.

I like that answer.

[geoexchangeman]

All these answers are good. The things that make high compressor ratios are the greatest killers. High compressor ratios are the number one killers says the compressor manufactures. Next in line is the wrong voltage either high or low. Flood back of systems with fixed bore metering devices is also up there from over charge. Refrigeration low back pressure unit are made to run with higher compessor ratios. But A/C Units are made to run with high back pressure and therefore lower compressor ratios. So if they are installed and have to operate with less than design air flow they will hit the graveyard quick. I can't leave with out saying a word about Geoexchange. They run with compressor Ratios of less than 2.5 to 1 in cooling some time as high as 3.5 to 1 in heating and have high and low pressure protection. Air source HP unit have to operate with compession ratios of 6 to 1 under normal conditions and let alone the conditions they get in when the HO don't keep the filters and coils clean. Add the defrost cycle, I don't see how the last as long as they do no matter what SEER rating they are. The low end models have only the internal overload to protect them. As I have said geo units love what they are doing and keep on doing it for many years after the warrenty is gone if the HO will just change the air filter. If not the unit will trip out on high or low pressure and must be reset because of the lock out relay. Is that a plus for Geoexchange.

[docholiday]

Originally posted by RoBoTeq

Originally posted by shophound
Compressors don't die; they're murdered.

Adding refrigerant brings the superheat of a system with low indoor airflow back to normal and allows the system to operate but with a reduced capacity and with possible slugging of liquid back to the compressor.

I think what you meant to say was it brings the suction pressure up to normal but the superheat will go down if you have low airflow and add refrigerant, which will lead to slugging. This is prevented by actually reading superheat and not charging by pressures alone.

[RoBoTeq]

Originally posted by docholiday

Originally posted by RoBoTeq

Originally posted by shophound
Compressors don't die; they're murdered.

Adding refrigerant brings the superheat of a system with low indoor airflow back to normal and allows the system to operate but with a reduced capacity and with possible slugging of liquid back to the compressor.

I think what you meant to say was it brings the suction pressure up to normal but the superheat will go down if you have low airflow and add refrigerant, which will lead to slugging. This is prevented by actually reading superheat and not charging by pressures alone.

In most cases this is correct. I was thinking of one particular instance where the technician made certain that the superheat was correct but ignored the fact that the suction temperature was on 2ºF. In this case, the suction pressure was also low but this tech stuck to his guns and make sure he had the correct superheat. Damnest thing I've seen. The unit was actually operational with solid ice all the way back to and halfway up the compressor housing.

[Shophound]

Air source HP unit have to operate with compession ratios of 6 to 1 under normal conditions and let alone the conditions they get in when the HO don't keep the filters and coils clean.

Hmm...let's crunch some numbers from the performance curves for a Trane TWA060C400A1 heat pump.

Heating mode, conditions as follows: OAT = 30°F; RAT = 70°F db; yields a condensing pressure of 180 psig (95°F SCT) and an evaporating pressure of 36 psig (15°F SVT), according to curves. Add 14.7 atmospheric for absolute pressures of 194.7 and 50.7 psia, respectively. 194.7/50.7 = 3.8

To approach a compression ratio under given conditions in heating mode to near 6, the head pressure would need to be boosted to at least 220 psig and the suction drop to 26 psig (yields a CR of 5.8). At this point your SCT would be ~109°F and SVT ~4°F, which means the indoor coil is ~40°F over RAT and the outdoor coil is ~26°F below OAT. Doesn't sound like the normal operating parameters the curves are looking for.

I I'll grant you that water and ground source heat pumps have the advantage of a fairly consistent condensing and evaporating medium, hence a lower compression ratio across the board.
However, I can't imagine an OEM of an air source heat pump willfully designing heat mode CR's of 6 or greater.

[MadeinUSA]

There is no way that unit could be operational with lines, and half the compressor frozen. In that circumstance on a R22 high temp system, the coil would have to be frozen solid with no air flow, therefore causing his low suction reading.

With a suction saturated temp of 2 degrees, his suction pressure was 25.6. His suction line temp being frozen would be 32 degrees, so 32 – 2 = 30 degrees super heat. Was this bozo thinking he was charging a car since his low side was at 25. I guarantee you Robo, on the phone he was telling you he had air flow, but you and I both know that’s impossible when you have a solid block of ice for a coil.

Not arguing here, we both know a coil temp of 2 degrees will produce a block of ice with R 22 in a high temp application.

Edit: Heck even in a R22 medium temp application, a 2 degree coil would be frozen on you, so a residential being it is high temp is darn sure going to be frozen solid.


[Edited by madeinusa on 03-17-2005 at 01:36 PM]

[RoBoTeq]

Evap coil was frozen solid and the system was operating. What will really get you is that this was a Goodman 10 SEER five ton system.

I have photos of this system but I do not know how to post them on this forum. I will start a thread elsewhere to show you this system.

Like I stated, I too was amazed to see this unit operational.

[tinknocker service tech]

trane has in its factorie in texas a compressor with a closed loop running for last i heard twenty five years with out ever beening turned off. i is a solid block of ice
and still runs. they say its hard to stop a trane
point being be it installer, service tech. home owner. power. charge. it stills comes down to one thing
human error is the main reason for compressor failure
my opinion only
do it right the first time or keep going back

[docholiday]

As I said.... Stress

[dash]

Originally posted by tinknocker service tech
trane has in its factorie in texas a compressor with a closed loop running for last i heard twenty five years with out ever beening turned off. i is a solid block of ice
and still runs. they say its hard to stop a trane
point being be it installer, service tech. home owner. power. charge. it stills comes down to one thing
human error is the main reason for compressor failure
my opinion only
do it right the first time or keep going back

That compressor,"Snowball",died a year or two ago.