Rebuilding a Cruisair FX16C condenser

[Milacron]

The discharge pipe temp is still useful by itself. Compressor manufacturers want to see a maximum internal compressor temp of around 300-350F and a discharge line temp of 225-275F implies that so you must be below that maximum to prevent overheat damage.

Ok, thanks. But for my curiosity, wouldn't the thermal sensor on the compressor body shut the compressor relay off before that point anyway ?

 

[Reefgeorge]

Eventually yes but if you want to maintain long compressor life you have to keep the discharge valve temp (as implied by the discharge pipe temp) lower than that. A discharge pipe temp below 225F is desired and should not trip the thermal overload yet, IOW the thermal overload switch will let you shorten the compressor life if you run it near the limit continuously. That said you have to be careful not to add too much R22 (which will lower discharge temp) because as the gas level goes up it helps cool the compressor to avoid the first problem but eventually you create a second problem which is liquid refrigerant making its way back to the compressor and slugging (killing) it. It's a balancing act between not enough R22 causing the compressor to overheat and too much R22 causing the compressor to process liquid and break. Thats why properly monitoring all of the parameters we have been discussing tells the whole story and makes sure that the system is optimized and will not go outside these limits at the extremes of operation.

The same can be said about the high and low side pressure cutoff switches. They prevent immediate catastrophic failure but their limits are so far outside of normal operation that if you spend a lot of time there you will kill the compressor. More modern electronic controls help to avoid this by shutting the system down after a number of out of limit events but older 3 knob systems dont do this. If your water pump keeps locking up and the system keeps shutting down on high pressure, then resetting and starting over you eventually damage the compressor.

 

[Milacron]

Eventually yes but if you want to maintain long compressor life you have to keep the discharge valve temp (as implied by the discharge pipe temp) lower than that. A discharge pipe temp below 225F is desired and should not trip the thermal overload yet, IOW the thermal overload switch will let you shorten the compressor life if you run it near the limit continuously. That said you have to be careful not to add too much R22 (which will lower discharge temp) because as the gas level goes up it helps cool the compressor to avoid the first problem but eventually you create a second problem which is liquid refrigerant making its way back to the compressor and slugging (killing) it. It's a balancing act between not enough R22 causing the compressor to overheat and too much R22 causing the compressor to process liquid and break. Thats why properly monitoring all of the parameters we have been discussing tells the whole story and makes sure that the system is optimized and will not go outside these limits at the extremes of operation.

The same can be said about the high and low side pressure cutoff switches. They prevent immediate catastrophic failure but their limits are so far outside of normal operation that if you spend a lot of time there you will kill the compressor. More modern electronic controls help to avoid this by shutting the system down after a number of out of limit events but older 3 knob systems dont do this. If your water pump keeps locking up and the system keeps shutting down on high pressure, then resetting and starting over you eventually damage the compressor.

Makes sense, thanks again. FWIW, this condenser uses digital controls but it is the SMX 1 style. My two newer condensers use the current SMX 2 style and I know the one time the seawater strainer got so clogged those shut down the pump, complete with overload alarm codes on the SMX 2.... but I never checked to see if the SMX 1 would do the same and/or show the same alarm codes.

 

[Milacron]

When I last posted I had only run the condenser maybe 15 minutes as I was in a hurry to go out of town and shut it down, but today I ran it perhaps 30 minutes and the compressor gets so hot on top it would burn my hand if I touched it more than a fraction of a second. So, something isn't right...wonder if it could be what killed the old compressor...

Did a seawater flow test via garden hose on the "water out" pipe of that condenser and it seems excellent....similar pressure/flow to that from a house outside spigot.

Although I'm a bit mystified how the seawater is supposed to cool the compressor as it is still amazingly hot even 30 minutes after shutdown, and the water flows even when it is off via the other units that are running.

 

[Reefgeorge]

Report back with those other numbers when you are able to get them together and we can see if there is cause for concern.

 

[Reefgeorge]

BTW, restricted sea water flow and/or a gunked up heat exchanger (poor exchange) manifests as high, high side pressure. PV=T, so poor condenser cooling equals higher discharge temps and since the volume of the system is not changing, pressure goes up on the other side of the equation. This is very easily demonstrated by restricting the seawater intake shutoff and watching the high side gauge while the system is running. It shoots up immediately.

The compressor takes the suction gas (65 psi or so) and compresses it which heats it up and passes it through the sea water heat exchanger which cools it down and that causes the hot gas to condense to a liquid on its way to the evaporator/metering device ( at 250 psi or so). There it expands and turns back to a gas which requires heat which it gets from the air passing through the evap coils (hence the cold vent air).

If you really want to know if all is well then we need:

Suction pressure
Suction temp near the service valve
High side pressure
High side temp near the service valve if you have a TVX metering device
Discharge temp a few inches from the compressor
Air temp into the evaporator
Humidity into the evaporator
Air temp out of the evaporator
Sea water temp

Get what you can and report back and I will explain more of the relationship between these numbers and what it tells us.

 

[jim rosenthal]

George, thank you for your contributions to this discussion. AC systems are mysterious to most of us, who may understand the general principles they work on but not know how to actually do this stuff. This is much appreciated.

 

[Milacron]

George, thank you for your contributions to this discussion. AC systems are mysterious to most of us, who may understand the general principles they work on but not know how to actually do this stuff. This is much appreciated.

Indeed, much appreciated here too. FWIW, yesterday I tried it in heat mode to see if perhaps the reversing valve was stuck....but it worked beautifully....heated the stateroom from 74 to 84 degrees in 15 minutes...maybe less. Interesting as condensor pipes that were hot were now cold....and yet the darn compressor still overheated. Gets so hot it surprises me the thermal switch doesn't trip. Anyhoo, reversing valve works....hopefully compressor problem is excess R22...but won't know until a week from Monday.

 

[Reefgeorge]

The compressor does the same work in the same direction in both heat and cooling mode. What changes (via the reversing valve) is that the evaporator and condensor switch places. The heat from compressing the gas is shed via the evaporator and the expanding gas takes the required heat from the condensing coils/sea water. I don't know which mode creates more compressor discharge heat, I will have to measure it sometime. The cold coils are physically closer to the compressor but the heat removal process from compressing the gas is now much further away.

 

[Reefgeorge]

George, thank you for your contributions to this discussion. AC systems are mysterious to most of us, who may understand the general principles they work on but not know how to actually do this stuff. This is much appreciated.

Glad to help.

 

[Milacron]

George, just getting back on the results of my HVAC guy fiddling with my condenser again. As it turns out rather than too much pressure, it didn't have enough...he borrowed an electronic leak detector and found another leak in one of the compression fittings. So he put in more R22 gradually while monitoring things and now it seems to be ok.

The compressor still gets hotter than I'd like but it's not too different from the others. For example it will get to 119 degrees on top, while the 10,000 BTU beside it gets to 109 degrees on top.

However that same 10K unit, which has been running and cooling great 24/7 for at least 2 months now, will show as high as 140 degrees at the smaller tube (where it exits the compressor body) and the new unit only goes to about 128 degrees there.

Anyhoo, the new compressor has been on 24 hours a day for 3 days now and still doing fine.....set on 74 degrees, so it's not running every minute...does cut off now and then when temp in room reaches 74...but runs, I'd guess, at least 21 out of 24 hours per day....maybe less as of yesterday, as nightime temps have finally gone below 80 degrees here.

FWIW, I showed him your specific tests to perform but he showed little interest in actually paying them much attention...so, sorry about not having answers to your specific questions on temps and pressures... suspect his attitude was "damn, can't believe I've spent so much time on this guys stupid condenser"... LOL.

Having said all that, if I had this to do over again I would order a new 7K BTU condenser from Ocean Breeze in Stuart, FL for aprox $1,450.... compatable with R22 or newer refrigerant and compatable with the original air handler and SMX 1 control as well. Would have been more money, but all new stuff and less labor*. But I didn't know about them until recently.

Regardless, many thanks for your info on this....very interesting stuff !

*Not just the leakages, etc. but things like me having to make a base for the compressor,etc.

 

[Reefgeorge]

Your discharge line temps are all well below the 225F max. Measuring the can top is not a very scientific measurement but it is used as a rule of thumb where I have seen a limit of 140F suggested. Try scanning your IR thermometer across all areas of the can top. There is a tremendous variation.

Marine AC units don't need to be as critically charged as other types of systems because they have accumulators and /or receivers which help to keep the system functioning properly in a wide range of conditions. Receivers keep liquid available for the metering device and accumulators prevent liquid slugging of the compressor.

I will have to look into Ocean Breeze.

 

[Milacron]

I will have to look into Ocean Breeze.

They have a good reputation. I talked with Joe there, who seems to know his stuff. For example, one of my Cruisair air handler squirrel cage fans (connected to a different condenser), every blue moon will not turn. So I have to take the seat apart on the flybridge and then unscrew many screws to take the top off the air handler box, just to get to that fan, spin the cage by hand to get it going again. It turns easy as new....I could probably blow on it to get it going. So I figure a new capacitor would fix it.

But Joe says, might not....he says the slightest wear in the plain bearings allows the motor coil to sometimes end up not perfectly aligned centered between the magnets, thus it doesn't start. Makes sense. Also interesting is they use a type of oil in the compressors that allows for R22 or more currrent refrigerant (410 ?). He says the only difference in the compatability is the type of oil used.

But back to the stuck fan... OTOH, had same problem with 5 ton heat pump unit at my office and replaced the start/run capacitor on that one and made night and day difference....went from fan not running at all (unless I helped it turn) to running fantastic...near instantaneous full RPM. So I still wonder if simply replacing the little black square capacitor on that Cruisair handler (Dayton fan) might not make some difference.

 

[Reefgeorge]

If the motor turns easily and runs well after a jump start then the capacitor might do the trick. If not, odds are that a proper replacement motor can be found. Just be careful, some control circuits don't do the variable speed thing well unless the motor type is the same (ex psc vs shaded pole). I just replaced a salon blower motor after finding the exact replacement in an unrelated wood stove blower.

 

[Milacron]

If the motor turns easily and runs well after a jump start then the capacitor might do the trick. If not, odds are that a proper replacement motor can be found. Just be careful, some control circuits don't do the variable speed thing well unless the motor type is the same (exsc vs shaded pole). I just replaced a salon blower motor after finding the exact replacement in an unrelated wood stove blower.

The model Dayton blower is only $170 for the whole thing so if a new cap didn't work I think I'd replace it all to save some labor messing with the motor/fan separately.

http://www.zoro.com/dayton-blower-3...gclid=CPGopaesoccCFYyQHwodXzwI3w&gclsrc=aw.ds

 

[Milacron]

Measuring the can top is not a very scientific measurement but it is used as a rule of thumb where I have seen a limit of 140F suggested.

You know what is bizarre, is that one of the 5 Cruisair units, a 12,000 BTU one that is 1993 vintage came with the boat, is actually cold on top the compressor ! Always has been since I owned the boat. And yet it works perfectly...cools the master stateroom and master head...stays on 24/7.

Hadn't occurred to be to check with the IR thermo exactly how cold it is on top, but cold enough it hurts a little to hold your hand on it !

 

[Reefgeorge]

The model Dayton blower is only $170 for the whole thing so if a new cap didn't work I think I'd replace it all to save some labor messing with the motor/fan separately.

http://www.zoro.com/dayton-blower-3...gclid=CPGopaesoccCFYyQHwodXzwI3w&gclsrc=aw.ds

That blower has a PSC motor as most new blowers do. The one currently installed may be the older shaded pole design which may be required for proper operation of your SMX controls (the variable speed part). That looks like the exact blower assembly that I needed and if it is, this assembly has the older shaded pole motor:

http://www.amazon.com/gp/product/B000BUGFKI?psc=1&redirect=true&ref_=oh_aui_search_detailpage

The key to compatibility is the voltage, amp draw and rpms.

 

[Reefgeorge]

You know what is bizarre, is that one of the 5 Cruisair units, a 12,000 BTU one that is 1993 vintage came with the boat, is actually cold on top the compressor ! Always has been since I owned the boat. And yet it works perfectly...cools the master stateroom and master head...stays on 24/7.

Hadn't occurred to be to check with the IR thermo exactly how cold it is on top, but cold enough it hurts a little to hold your hand on it !

When the compressor is freezing on top or at the inlet that usually means that you are overcharged which is as common than undercharged. Most people believe that the cure for all refrigeration problems is more gas and many times it is not. Make sure that all blowers are running for that condenser, the cages are clean and that the evap coils are clean. Also make sure that the lowest fan speed has not been lowered too much. The reason for all of this is to make sure that the evap(s) is(are) doing enough work so that the liquid R22 is being completely flashed back to gas on its way to the compressor.

 

[Milacron]

When the compressor is freezing on top

No frost there...never that cold...but I suspected there was a "bad" reason it is doing that and appreciate the confirmation. Will investigate it further.

 

[Milacron]

No frost there...never that cold...but I suspected there was a "bad" reason it is doing that and appreciate the confirmation. Will investigate it further.

48 degrees....surprising how cold 48 degree steel feels.