New sound from Carrier HP - like an ice cube in a garbage disposer

[dale_k]

The new sound seems to happen when the unit is off for a pretty long time in cool weather. When it cycles on in heat mode, for about the first 10-20 seconds there's an intermittent sound sort of like tossing a single ice cube in the garbage disposer. Kind of a grinding/chewing noise, which goes away after a short time.

Is this the compressor "sluggiing" on liguid refrigerent? Any other ideas. It's definitely not coming from the fan hitting a twig.

[woody19]

Yes, it sounds like liq. slugging. You may want to install a crankcase heater.

[docholiday]

Carrier does not charge any extra for the entertainment value. All kidding asside, I agree, if it's happenning at start up, a CCH should resolve it.

[dale_k]

Funny it hasn't done it before since the system is 2.5 years old. Maybe it has a heater that's died. I've noticed one other symptom and I have a homeowner theory for how they are connected....

This unit never stops trying to defrost, no matter how warm it is outside. In fact it went through a defrost cycle a few minutes ago when the outdoor temp was 70. I only ran it to see if I could recreate the ice cube noise on a fresh call for heat. Here's my theory - if there is an ambient temp sensor in the system and it's failed, that might explain why the system tries to defrost in warm weather. It might also explain why the crankcase heater (if one is already in the system) doesn't activate when it needs to. Go ahead and laugh - 99% of homeowner theories are wrong.

[docholiday]

Certainly you may very well be onto something. Hard to say from here but the checks for flooding are simple, defrost control and operation are also simple to look at. Unfortunately without looking at it, I dont know Carrier's defrost strategy.

[I_bend_metal]

I thought all Carrier heat pumps had crank case heaters?? Sounds like yours might have took a crap on you....well not ON you but....well....you know what I mean.

[dale_k]

To bring some closure to the thread, the tech just left a few minutes ago. The unit would not make the noise, which is natural since it is 66 degrees. He checked a few things, put the gauges on the system but didn't find anything. He told me my Carrier does not have a crankcase heater whereas a Trane would have one. He seemed to believe me that I heard the noise.

I doubt the unit will have any trouble since we're almost in A/C season but the noise will probably come back in the fall if my slugging theory is right. I'll try and come up with a way to take a little movie with sound so at least the tech can hear what I hear.

He also said the Carrier did not have an ambient temp sensor to prevent the defrost cycles in mild weather.

[BigJon3475]

IMO all HP's should have crank case heaters....and in some cases straight A/C also.

[beenthere]

Heat should have forced it into defrost to see if it would terminate the way it should.

Hopefully, the next tech you get, won't just compare yours to another brand, instead of finding the problem.

[dale_k]

Heat should have forced it into defrost to see if it would terminate the way it should.

Hopefully, the next tech you get, won't just compare yours to another brand, instead of finding the problem.

He did force a defrost. Of course the unit makes a whoosh noise and then for a few seconds the scroll compressor growls slightly at the start of the cycle. He wanted to know if that was the noise I heard. I told him no, that I heard more of a grinding noise.

My question about the defrost and ambient temp was not so much that the defrost terminated OK, but why it would go into defrost at all under mild temperatures. With my previous HP's, a Ruud and a Trane, the unit would not begin a defrost cycle in temperatures above 50.

The tech seemed to believe me and he checked several things, including the switch settings on the indoor coil to be sure they matched the outdoor unit. My guess is the lack of crankcase heaters permits the accumulation of liquid refrigerant under conditions when the outdoor unit doesn't see a call for heat for many hours in outdoor temps in the mid 40's. Looks like Carrier built a crummy unit. I'll probably avoid them in the future.

[thorton]

Your unit may not be going into a full defrost cycle in high ambiend temps. First things first though, your not suppose to be operating a Carrier heat pump in heating mode in temps above 66 degrees F unless you set your stat to emergency heat mode. These units are equiped with a heating vapor pressure limiting device. "PressureGuard", which cycles the outdoor fan at high ambient heating conditions. So what I'm suggesting is your unit may not be going into a full defrost as often as you think and it might be the fan cycling off and on. As far as a crankcase heater, yes your heat pump should have one if used in cold climates, but are optional on Carrier models at an extra cost.

thorton
______________________
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[BigJon3475]

Your unit may not be going into a full defrost cycle in high ambiend temps. First things first though, your not suppose to be operating a Carrier heat pump in heating mode in temps above 66 degrees F unless you set your stat to emergency heat mode. These units are equiped with a heating vapor pressure limiting device. "PressureGuard", which cycles the outdoor fan at high ambient heating conditions. So what I'm suggesting is your unit may not be going into a full defrost as often as you think and it might be the fan cycling off and on. As far as a crankcase heater, yes your heat pump should have one if used in cold climates, but are optional on Carrier models at an extra cost.

thorton
______________________
Birthdays are good for you
the more you have the longer you live




They aren't just for cold ambient conditions.....from Bristol:

"5.1 High Ambients
If crankcase heater wattage is inadequate, high ambient temperatures (greater than or equal
to 80°F) coupled with high solar load on the system condenser coil (no louvers) can cause
refrigerant to migrate out of the condenser, in reverse, back into the discharge line through
the compressor valves to the lowest temperature area of the system. During this reverse
migration, refrigerant can liquefy in the cylinders of the compressor which can result in a
start-up slug. To minimize this effect, the crankcase heater needs to maintain the sump at
least 20°F above the highest temperature in the system.
Other wide differential temperature circumstances to consider are:
¨ Building under construction, i.e., no cooling (evaporator warmer than condenser). Also
see Ground Source Heat Pumps (Application Bulletin 134).
¨ A split system evaporator is normally in a cooler location, while a rooftop package
system evaporator is in a much hotter location and could be even hotter than the
condenser on initial start-up and after extended shut-down periods. This condition can
allow refrigerant to fill the vital parts of the compressor, resulting in a start-up slug even if
the system charge is within the published limitation.
5.2 Low Ambients
At low ambients (less than or equal to 60°F) and low condenser solar load, refrigerant can
migrate from the evaporator through the compressor to the condenser. Again, refrigerant will
tend to liquefy in the cylinders of the compressor. The crankcase heater needs only to
maintain the sump at least 5°F above the lowest temperature in the system to minimize the
effect. The lower ambient will allow refrigerant to flow out of the compressor at a faster rate
than at the higher ambient."

[dale_k]

Thanks for the info. I was aware of the limitations on heat mode above 66 but sometimes I forget to turn it off and the heat will cycle for a short time. That doesn't take place very often.

I've never seen the outdoor fan cycle independent of the compressor. I'm positive it goes through warm weather defrost cycles because I hear the woosh of the reverser valve. Yesterday I read the installatiion manual and saw something about the defrost thermostat so I pulled the service panel off and looked inside. The defrost thermostat they were talking about is actually a coil temperature sensor. It is a defrost thermostat but it doesn't prevent defrosts in warm conditions - it ends the defrost when the coil temperature gets warm after the frost has melted. I didn't see any ambient temperature sensor, which confirms what the technician told me.

This morning I tried to take a video with sound of the problem I'm noticing. It was in the low 50's, the house was 67 and the unit had not run in about 24 hours. The heat set point was 66 so it hadn't come on. Anyway, when I raised the setpoint the unit came on but no horrible noise like before. It was actually in the 40's the 2 times I heard it before. Those conditions don't reoccur very often so it's not like I'm seeing slugging every day.

I may go ahead and authorize them to install a crankcase heater. I notice some yellow and black wires going into the compressor and a pair of red wires but I really don't know what I'm looking at to verify whether the unit already has a crankcase heater that has stopped working vs. never having one in the first place. It probably never had one since the Carrier installation manual says it's an option.

[4l530]

Originally posted by dale_k
My question about the defrost and ambient temp was not so much that the defrost terminated OK, but why it would go into defrost at all under mild temperatures. With my previous HP's, a Ruud and a Trane, the unit would not begin a defrost cycle in temperatures above 50.

The defrost control here is "time / temperature".
At a chosen interval (you can choose 30, 60, or 90 minutes) the board will check for the defrost thermostat to be open or closed.
If its' closed, the unit will do a defrost.
The defrost thermostat closes at 28° and opens at 80°. 28° is cold enough to begin to develop frost, no matter what the outdoor temperature is.

I would not be suprised to find that your unit is undercharged, and / or maybe the coil could use a cleaning. Putting gauges on it won't tell you a thing unless you also take a few temperatures here & there, if all you do with the gauges is look at them without getting some temperatures, then you don't know any more about it than you did when you started.



Looks like Carrier built a crummy unit. I'll probably avoid them in the future.

They all build crummy units. Don't let anyone try to fool you about that.