Freezing suction line

[Reefgeorge]

I have a 2002 16k btu Cruisair remote dx unit that has the following problem. The charge levels are running well below the chart guidlines at 48 psi suction and 175-200 psi liquid. The evaporator delta t is 18-23 degrees. The filters are clean and the airflow seems reasonable. The unit cools well starting at high load and superheat is running high at 30-40 degrees but as soon as you hit a normal evap load (78 degrees and less than 50% humidity), the superheat crashes towards zero and the suction line starts freezing at the suction service valve. The low suction pressure and initial high SH suggest a low charge but thefinal cooling stage at low load act like an overcharged system or a system with low evap airflow. Where do i go from here? Thanks,

George

[krush]

You go to a pressure/temp chart and see that 48psi on r22 is about 25 deg F...which would mean you are freezing the condensation. The superheat is so high because you are undercharged.

When the evaporator turns into a block of ice, your superheat goes to 0 and your suction line freezes. And it acts like low airflow over the evap because your evap is a block of ice!

You need more charge. I'm not the local cruiseair expert, but I think your unit is fixed orifice, not TXV....so measuring superheat is appropriate.

This is why we tell people you can't just charge by pressure and say "Oh, just get XX psi on the low side and you are good". There is lots of stuff that has to be interpreted on them gauges--it ain't rocket science, but most people don't understand it.

PS: My simple redneck way of charging a fixed orifice unit if I don't feel like measuring super heat and using a sliderule or HP calculator...charge till I get some cold coming back to the compressor. If your compressor is sweating, you am be a little overcharged.

[Reefgeorge]

I take it then that you are never done charging if the saturation temp on the suction side is less than 32 degrees (58 degrees) because once the evaporator runs out of something to do (near set point, fan on one speed segment, humidity low, low temp load), the below freezing sat temp will translate into a freezing evap/suction line?

As an experiment, i lowered the charge to the minimum that would cool the cabin and meet the evap delta t min of 15 degrees. That turned out to be 44 psi/20 degrees. The cabin was cooled, the superheat was 35 so the suction line was cold to the touch and sweating and the superheat did not crash to zero at low evap load (end of the cabin pulldown). I know that if i increase gas past this point, evap delta t will go to 20-23 degrees and the system will freeze at low load. This would suggest that i need to push past all of this to a sat temp above freezing and a starting high load superheat around say 10-20 and have the faith that after the cabin pulldown and low load condition, the superheat will stay put because the evap cannot freeze and i will not slug the compressor?

So freezing occurs in a middle band of low charge below which there just is not enough gas to freeze the coil despite the low theoretical sat temp and above which, freezing is not possible, just floodback/slugging if you go to high?

BTW, what line temp range equates to "cold can of beer" cold becuase a can of bear comes out of the refrigerator at 37 degrees and, depending on the humudity, will still be sweating up to a temp in the 60's?

Thanks.

[krush]

Slugging: I've done a lot of dumb things and still do dumb things, but I've never slugged a compressor--and this includes charging with the 30lb can upside down so I can get to drinking beer faster. Now that I said that, I'll probably have it happen. The way the compressor are designed is that the suction goes in the bottom of the "can" the inlet to the compressor is pretty high from inside that can. In other words, you'd have to overcharge pretty damn high to slug the thing. There is time for the left over liquid to evaporate in the bottom of the compressor...plus there is an accumulator....but I digress.

Anyway, to give a simple answer to your thought process. Unless the ambient cabin temp is really cold (which I presume it isn't) your coil temp should not be below freezing...you have an A/C system, not an icebox.

Are you positive you have good flow and your evap coils aren't dirty? Your latest experiment kinda points to that. With good airflow you shouldn't be able to freeze the coil under normal conditions. With a low charge, coil freezing may happen if the ambient temp gets low enough and the cooling load on the unit is low enough.

A very high superheat means that your compressor isn't getting good cooling. This is the problem with low charges--the compressor will overheat due to lack of cooling.

[REBrueckner]

I've never known as much as I'd like about air conditioning but the advice above is right on...a freezing coil for me means to check air flow (is the fan running and air moving) and if that's normal, likely I am undercharged....

[Reefgeorge]

Yes the filter right on the evap is clean as is the rough metal filter in the grill. The fins are shiny like new (my wife has asthma so we have to keep all ac filters squeeky clean and run HEPA filters in the boat and at home). The airflow to both ceiling grills seems to be normal (ceiling intake/evap coil/fan(s)).

Here are the results of yesterday's experiment at the 3 hour point(cabin started at 93 degrees, external temp 90+) and your probably right about the hot compressor:

Sucton P/T 44psi/19F
Head P/T 200psi/102F
Evap delta T 15F
Indoor dry bulb 78F
Indoor humidity 45%
Cooling water 84F
Engine room temp 84
Ending Superheat 38F
Subcooling 11F
Compressor temp 212F
Compressor type Tecumseh AKA8515EXD

I do notice that in the previous case where the charge was a little higher and the suction line freezes, as the superheat tanks to zero the compressor starts making more noise so I thought that this was the start of the slugging process? Given that these systems have an accumulator, it makes sense that these things should be pretty immune to extreme variations in conditions.

BTW, the other unit has a frozen compressor. 2 questions:

Does increasing the start capacitor value to have a "harder start" capacitor ever get these things going for some additional life without overloading something? All the windings ohm out OK, no shorts, no opens. The compressor cycles on overload shutdown and high amp draw. I replaced both capacitors, the relay and the triac. Pretty much everything except the logic board and the compressor. No luck. If this is dead-dead, what is your take on a new unit with 417A, evacuate the 417A and start over with R22? Are there any drawback to replacing the 417A?

Thanks.

[krush]

Also, where are you getting your temp measurement for superheat?

Edit: On the locked compressor...try banging on it--yes I'm serious. You should be able to find a locked rotor current spec as well. Maybe steve, the A/C guy can help with that.

[Reefgeorge]

A thermocouple/clamp on the suction line just before the service valve/port.

[krush]

Is that near the inlet to the compressor or is it closer to the evap? My reason for asking is that the superheat will only go up as you get closer to the compressor. 212degrees is pretty dang hot too!

If you are sure the coils are clean, the blowers are working right, and no clogged filters...I'd say you are showing symptoms of a low charge.

Here's some theory and charts if you are interested: http://www.achrnews.com/Articles/Feature_Article/e0b126071885a010VgnVCM100000f932a8c0

[Reefgeorge]

Its at the inlet to the condensor unit, at the end of the copper run from the evap coil. That puts it 1 foot away from the compressor and 20 feet from the evap coil. Given that superheat is going up by the time it gets to the compressor, if I read 0 here, it is definitely zero all the way back to the evap coil.

Have you ever tried a "harder" start capacitor (read bigger than spec) to revive a frozen compressor? I'll get out the rubber mallet and give it a whack while it's cycling on no start/thermal shutdown. If it starts, won't it just freeze again, or can the hammer act like using a defib unit and give me a few more years (assuming that I stop eating cheeseburgers)?

Thanks.

[Boatsb]

These compressors are cooled with the suction line freon. If it is 200+ degrees that's just another sign of low freon.

Why not charge it to the proper levels and see if it works? It seems all this discussion is going no where unless you get the pressures where they should be.

[Reefgeorge]

Well I went back down to the boat after 18 hours with the "minimum" charge scenario and after the system was able to pull out the rest of the humidity and get to minimum load, it froze up again. So besides the hot compressor problem, the unit still freezes eventually. This charge level can cool the cabin but has these other performance problems, but you already knew that. I was not able to try the higher charge scenario, I'll post back when I get to it this weekend.

In the meantime, with the frozen compressor on the other unit, I'll bang on it to see if that helps. Can increasing the start capacitor value help without other problems? Tecumseh says that you can go up one capacitor value from 72-88 to 88-108. Any higher? If that unit cannot be salvaged, how do you decide on compressor vs entire condensing unit? If its whole condenser, are there any problems reclaiming the 417A and replacing with R22?

Thanks.

[krush]

Any updates? Just curious to see if the problem got solved.

[Reefgeorge]

Actually, further complications developed - the cooling sea water pump failed and is very difficult to access and replace. I'll be down there tomorrow continuing to R/R the pump and then it's back to charge levels and frozen compressors.

[Reefgeorge]

I finally got the cooling water pump replaced and fired up the system. I set the charge at:

81 degree sea water
78 degree indoor dry bulb
40 percent indoor humidity
23 degree evap delta T
11 degree sub cooling
58 psi suction
220 psi liquid

As the cabin gets close to set point, once again the superheat goes to zero. BTW, superheat started at 25 degrees at full cabin load this time, in line with the chart. I tweaked the charge at the end to keep the suction saturation temp just above 32 degrees.

[krush]

How many pounds did you put in? I always try to use a scale to at least get an idea how much I'm putting in a system. It's just another tell-tale tool to use.

[spcoolin]

George~

With your water & air temps as described...I would expect to be running 73-74 psi suction & around 235 psi head...

As I said over at my site...Compressor temp is important...Not enough refrigerant return will cause it to run hotter than nominal, and damage the compressor.

When you try again...It's not likely that the seawater temp has changed much (however the cabin temp will)
Forget about sub cooling & superheat for now...You are not even in the neighborhood of being fully charged yet if all is well in the system...

Try charging to 235 head and see where your suction runs...Depending on cabin temp above 70 degrees...I would expect the suction to be running anywhere between 62-75 psi...
Then watch compressor temp...If it starts getting cold...Remove a bit of freon...
If the compressor temp starts climbing to say 120 degrees...Add a bit more....

The most important thing to do is charge for compressor temp...Then we can talk about TD's & such...

BTW, your TD should be no more than 18 degrees & no less than 15 degrees...

Steve~

[krush]

I'll gladly defer to Steve...listen to him!

Not that it matters, but I agree with him 100%...still undercharged. If you are scared of overcharging, get a scale to keep track. I'm sure Steve has a ball park figure to use.

[Reefgeorge]

OK, I'll ignore SH and charge to the Cruisair charts while looking for a maximum compressor temp of 120 degrees and a minimum head pressure of 235 and report back.

Is the compressor temp measured on the top of the can where it is hottest or somewhere on the side?

I forgot to include it but the top of the compressor case was running 180 degrees, but you already knew that it was still too high.

Thanks.

[spcoolin]

On the top George~

You can start to tell you are getting overcharged if the compressor can around the suction tube on the compressor starts to sweat...The more you overcharge...The bigger the circle of sweat gets around that tube...Ideally you want the line cold, but no circle of sweat on the can...However a small circle at lower cabin temps is ok...And at this point...The pressures are what they are...We can then interpret what is happening in the system by reading them, but not until we know the system has enough refrigerant to properly cool the compressor.

Sub cooling & superheat are great tools for charging air cooled systems where you may not have access to the compressor due to the fan blades spinning...But they are really not needed in this case with a R-22 system that you can access the compressor...

These Cruisair systems (as most R-22 A/C systems) are designed (cap tube & air flow sized) so that they should run above 32 degree evap (58 psi) down to around a 68-66 degree cabin....Even when properly charged, they will ice in ambient temps below that, and of course reducing air flow such as undersized duct, or slow fan speeds (reducing the amount of heat picked up) can raise that point of icing into the 70's...

This is why the SMX control has a de-icing algorithm that shuts off the compressor for progressively longer periods (before setpoint is reached) the lower the cabin temp is below 70 degrees...It's described in the SMX manual...

But what I'm getting at here is...The lower the cabin temp...The lower the suction pressure (and thus evap coil temp) will go...Therefore with a warmer cabin you must start out with higher suction pressure to allow for the decrease in pressure & temp as the cabin cools...

The 15 to 18 degree Temp Differential (TD) between the air entering the air handler, to the air exiting the discharge grill will always be maintained...And this is where most people get confused in thinking their A/C is not doing as well as it should...

The warmer the room temp...The warmer it comes out grill....
If the cabin is 90 degrees...Don't expect lower than about 72-75 degree air out of the grill....But if the cabin is 70 degrees you might have 52-55 degree air out...

Steve~

[Reefgeorge]

Could not be any more clear than that. I'll report back tonight after I follow your instructions.

These systems are definitely not residential split air cooled systems and a new learning curve is needed. Thanks for all your help so far.

[SKYCHENEY]

Thanks Steve, that is great information. My old automotive gauges show a range for both R12 and R22 pressures, but your information makes it much easier to get it right.

[Reefgeorge]

I ignored everything else and charged to a compressor temperature target and stopped when I got close and additional gas did not increase suction pressure. The results:

Compressor temp (top of can) 122F
Suction 65 psi
Hi side. 243 psi
Water temp. 88F
Indoor DB. 81F
Indoor humidity. 39%
Evap delta T 22F
SH 0
SC 12

I need some help with watching the suction line input to the compressor. These units are tucked away so tight that I cannot follow the refrigerant flow. Where can I see a diagram of the refrigerant components and placement?

Any other comments?

[spcoolin]

George~

You are getting close...But the other day you said you had 81 degree water not 88...With that temp seawater your head should be 250 psi or over, and with a cabin temp of 81, I would expect a suction pressure of 70 or so...

I know of no diagram that shows what you ask...Can you get a hand in there to feel the compressor top & side around the suction inlet ?...It should be at top left of the can...Feel for the sweat circle I described...

What concerns me is your TD at 22 degrees...It should be no more than 18 degrees...which tells me you are not picking up enough heat....

This is where it is important to know about the charge and if you have flood back at the compressor inlet...It's also important to know a few other things about the system...

What model air handler do you have ?...If you don't know...Can you tell me if it has propeller type fan blades, or a squirrel cage blower ?

What size is the duct as it leaves the blower ?...A 16K requires 7" duct, a total grill area of 80 square inches, and a return area of 140-160 sq inches.

At the pressures & temps you quoted this time...Was the fan running fast ?
All testing we do now should be with fast fan, so that we take the loss of heat pickup of low fan out of the equation...

Steve~

[Reefgeorge]

I am near an inlet so water temp varies with tide cycles. I measure it with each charging event.

The fan was forced to full speed.

I will measure the intake and output grill sizes the next time I go to the boat. It is all factory original as installed by Cabo. The air handler is a dual fan model with two discharges/ducts going to two output grills on either side of the salon. The intake and outputs are all in the ceiling of the salon. I do not know the AH model or the fan blade style.

So the suction line input to the compressor can is at the top left of the sealed can when facing the electronics box/base valves (front) of the condensing units?

I plowed through all of the Cruisair documents on this and related units and came up with the following possible refrigerant flow for my condenser. Is this correct?:

Suction base valve-suction accumulator-compressor-condensor-receiver-dicharge base valve.

Thanks.

[spcoolin]

I am near an inlet so water temp varies with tide cycles. I measure it with each charging event.

The fan was forced to full speed.

I will measure the intake and output grill sizes the next time I go to the boat. It is all factory original as installed by Cabo. The air handler is a dual fan model with two discharges/ducts going to two output grills on either side of the salon. The intake and outputs are all in the ceiling of the salon. I do not know the AH model or the fan blade style.

So the suction line input to the compressor can is at the top left of the sealed can when facing the electronics box/base valves (front) of the condensing units?

I plowed through all of the Cruisair documents on this and related units and came up with the following possible refrigerant flow for my condenser. Is this correct?:

Suction base valve-suction accumulator-compressor-condensor-receiver-dicharge base valve.

Thanks.

Yes...Top left when looking at electrical box & service valves...

That sounds about right except insert "reversing valve" in between compressor & condenser...

I say this without being there, but I still feel you are a bit low on R-22 given your most recent data...

Never assume the boat builder did a proper install...Most don't...
I did tons of warranty service here on the West Coast of Fl when I was with the Cruisair distributor...90% of the warranty problems were from Boat Builder's improper installs & restricted...Something...

The politics made it doubly hard...The customer wants what is right, and for the system to work as it should...Cruisair has little control over how a system is installed...Also the Cruisair salesman does not want to stir the bucket & make them change for fear of loosing the account...

We had to try to avoid telling the customer what was wrong (just get it working) until we contacted the salesman for that builders account & Cruisair service/warranty dept...Then the guys up there would hash it out & tell us what to do...Most times it was the warranty/service dept that would get back to us about what they would pay for and they (Cruisair) would cover it...How they worked it out internally I can't say...Other times the boat builder would have to pay if Cruisair denied the claim as not the fault of the equipment...But not often...Even though it was the builders problem...Cruisair would end up eating it...

Hell...If it was me that sold & installed the equipment incorrectly, and it didn't work as designed...Guess who had to go back on his nickle to make it right...or if out of my area...pay someone else to make it right ?

No Marine A/C company's warranty dept or coverage was better...They really did want the customer to have what was right even at their cost...As I said...How they charged it out internally to sales or whatever...I can't say...


My feeling was always...The poor install only made Cruisair equipment look bad...Not the boat builder, or Cruisair salesman that let them get away with installing it that way it in the first place...On multipule boats I might add...and many of the problem installs were never caught/reported until after warranty had expired...

Steve~

[Reefgeorge]

Point taken

[Reefgeorge]

I left the AC running for a week and found the following yesterday:

Water 79F
Indoor Air 76F
Indoor humidity 42%
Evap delta T 21F
Suction 58 psi
Compressor temp 119F (hottest point on top)
The compressor temp at the coldest point on top near suction inlet is 35F.

The inlet on mine is at the top right and I can barely see back there. I have to use a mirror and flashlight. It is sweating at the input point but I can't see how much. When I first got down there and the unit had been running all day, the sweat climbed across the top of the can in a semi-circle near the inlet about 1" and was partially frozen. The hottest spot on the top was 115F.

George

[spcoolin]

George~

Sounds like you may have the older Copeland compressor that they used in the 16K unit up until around (guessing) 1982-83...Are the electrical connections & cover on top of the can ?
That Copeland compressor was not as efficient as the Tecumseh but it was practically bullet proof...Though not good...I would be less concerned about some liquid slugging back if in fact it's the Copeland...

Or to your knowledge...has the compressor been changed out previously ?

I still think you are not picking up enough heat...This is where we start to look at air flow, and or...Refrigerant flow & possible restriction in that circuit...
With all this charging & adjusting we could also have moisture, or non-condensables in the system...Do you have a vacuum pump ?

Mis-matched components too...Gonna need a air handler model # and Compressor model #

Steve~

[Reefgeorge]

The compressor is OEM original. Tecumseh AKA8515EXD. No connections on top.

This unit has been sweating/freezing at the suction input to the compressor for a while because there is a rust streak down the side of the can so your right about the tolerance to flood back.

Yes I have a vacuum pump, reclaim machine and canisters. I thought about the non-condensables but doesn't that usually result in pressures that are higher than expected?

Where is the air handler part number? It is an overhead unit with 2 blowers. This is another unit that is hard to get at.

I thought of one explanation for the low load situation at the end of the pull down process. About 6 years ago I changed the fan over to intermittent and installed a temp probe/sensor in the cabin. This significantly lowers the humidity vs when I had the standard set up with full time fan and the probe on the evaporator. This is probably a significant reduction in the design point latent heat load, particularly at the end of the cycle. I did this because we have asthma and severe mold allergies in the family and this helps a lot, except of course from the point of view of the compressor. What do you think?

[spcoolin]

George~

Either I missed it, or you didn't mention the head pressure in your last data report...So I can''t really answer the Higher than "expected" question...

I also need to know if you were running low fan speed at those figures...My question there being...Low fan speed may be programmed too low...

A test you could do to see about non condensables...
Shut the system off & let it equalize...Then with a helper & gauges connected...Have the helper start the system while you monitor the gauges...Look for the head to climb up and then drop before suction falls much...Then both to pull down together...That's a sign you need to evacuate.
On initial equalized start...The head should climb and pretty much stay at one point until some heat has been removed but it should not drop rapidly.

I don't feel your temp sensor location or programming for intermittant fan has anything to do with it unless the temp of the air that is actually returning is much lower than what you are reading...IE: cold air leaking back from the discharge into the return path thus causing the system coil to see much colder air then cabin temp...This would be a cause for low suction & icing...

Steve~

[Reefgeorge]

Fan was on high.

Evap input temp is reliable.

This was the first set of readings that i did without hooking the high side gauge because i am monitoring for leaks and did not want to disturb the charge levels with the high side hose fill. With that said, all previous high side readings seem reasonable for the conditions. On my next trip I'll try the "dynamic head test". Are those Mainstream quick test kits for real time acid detection any good?

This system would appear to be oversized. Is there a way to lower the effective capacity with say a metering device change? What happens if you install a smaller compressor and leave the evaporator as is? In another thread you have been advising me on my locked compressor in the other system which needs attention as soon as this gets resolved. I don't know if I have the same problem there but I am going to try some larger start caps to see if I can get some baseline numbers before surgery. That system probably does have moisture in it. Years ago an A/C company did an evaporator changeout without evacuating the lines. I don't remember if they at least swept the lines before restart but I suspect that this might explain the dead compressor. I was not very HVAC savy back then or I would have put up more of a fight on proper proceedures.

[spcoolin]

George~

System size to Cabin size should have little to do with this...As I said before...These systems are designed for the single cap tube to provide above 58 psi suction with temps above 68-70 degrees in the cabin...

No matter the cabin size it's the temp of the air that returns to the coil that does.

If you go with a larger metering devise...Yes you will raise suction pressure & lower head...But also may cause more liquid flood back...

We have however, In dual air handler installs (one remote slave) put as much as 17K BTU on a 16K unit (like a 12K + a 5K or a 10K + a 7K) but never more than 1000 BTU over on that 16K unit...Also never any less than 16K of evaporator load or you get what you are experiencing.

If I'm correct in assuming what overhead air handler you have...I forget the model (think it was EDS16 or ESS16) but It's in a metal box, is say 4-5 foot wide, & has dual air outlets...It should have two of what we call "EBO8" air handlers inside (8K each) the return is in the center of the two with a foam covered diverter mounted inside that return...

All it would take is one of those EBO8's to be leaking discharge (cold air) inside the box and back onto itself or the other EBO8.

It could also be that one of those EBO8's has a restriction at the cap tube or cap tube strainer/s (one strainer at each end of the cap tube) and therefore one is not feeding properly...

What I might try to do is remove that diverter so that you can IR gun test coil temp on each coil from bottom to top...Compare them...

Another simpler test would be to test outlet temp at each grill...But I would not use a IR gun for this since they really are only good for sensing surface temp...Not air temp...and the above test would be more telling...

Once more...You can re-design if you want...But the original design worked well if there were no installation flaws or other factors such as junk in the system causing restrictions...Hell a cap tube strainer can clog from someone oxidising the inside of the copper with a torch when making a sweat joint at installation...After the copper cools and the system is put in operation...That oxidation crud migrates around with the oil & refrigerant until it lodges at the cap tube strainer...Enough of it will plug that strainer, but it takes more junk to clog a strainer then it does a cap tube...That's why they installed the strainers.

One more thing you can try is...Run the system in heat to try & clear a strainer...This will cause the crud to flow back the other way & maybe lodge somewhere else...If the problem goes away...but then comes back...You'll know it's something plugging the strainer...Which one should be evidenced by the coil temp test...

Steve~