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Suction line freezing
February 17, 2012
10:49 pm
reefgeorge
Melbourne, Fl.
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I see that I never posted a final summary. I eventually charged the unit until I met the 120F compressor temp maximum and 58psi suction minimum and tried that charge level for a while (still below the charts on suction psi). Well awhile is now coming up on two years without a single problem. As a matter of fact I have never gone this long without needing to look at the charge and I have been through two winters with heat operating without compressor cycling on extreme weather cabin warm ups. Thank for all of your help and getting me off of residential HVAC targets and on to marine AC guidelines.

 

Next topic. I still have not addressed the frozen compressor on the other unit. My current thinking is to use the same frame and electronics (caps and board are all new) but replace the compressor, dryer, exchanger tubes and possibly the access ports. A few have said that compressor and dryer only for a 10 year old unit is dicey because of the potential for exchanger leaks. Is this approach workable? Are all of the parts still available. Its a 2002 vintage packaged 16,000 btu Cruisair unit.

 

I guess another option is to avoid a rebuild by purchasing a complete compressor rack replacement which would ship with R417a refrigerant. As I understand it R22 uses mineral oil and 417a can theoretically use mineral, POE, or AB oil so the 417a based replacement condensing unit would be a direct drop in replacement without an oil compatibility problem as long as this new unit is shipped with 417a and mineral oil. is this the case?

Thanks,

 

George

June 2, 2010
8:39 am
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Steve Pooler
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Check your mail George...I'm headed out to work for the day...Will check back later..

Steve~

June 2, 2010
8:11 am
reefgeorge
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Steve

i can't get the contact form to work on this phone.

** you don't have permission to see this link **

June 2, 2010
7:28 am
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Steve Pooler
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George~

I can't quote discounts here, but if you want to shoot me an e-mail thru the Contact Steve link at the top of any page...I'll respond...

Thanks,

Steve~

June 2, 2010
7:02 am
reefgeorge
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Steve

What factors do you consider when deciding if a compressor change out is a good idea vs. the entire condenser? What are the discounted prices of both options and where do you ship from?

Thanks.

June 2, 2010
6:37 am
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Steve Pooler
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George~

I think you are pretty much wasting your time & money to get the locked compressor turning over...The damage is already done, and even if you do get it running, it's likely to quit very soon after...at least in my experience...

I know of no problem evacuating the 417a & recharging with R-22...Same compressors, Same oil...

A Replacement compressor is $695 Cruisair #3101-16T with tubes & burn out drier..Tecumseh # AKA8515EXA ...Plus labor & refrigerant.

Make sure if you have a 16K unit that you only use that compressor...Supply house matches don't work out well at all...Trust me on this.

A replacement 16 condensing unit for operation with SMXII would be a RX16-417 at $2240.00 retail (I can discount this)

I don't know the condition of your existing unit so that would be your decision on which to do...

Steve~

June 1, 2010
7:35 pm
reefgeorge
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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, I have a frozen compressor on the other unit. 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? Kush suggested hitting it so I'll try that as well. 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.

June 1, 2010
9:58 am
reefgeorge
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Steve

Thanks for all your help so far, I'll charge to more "normal" pressures and see where we are at and report back. Now that I know that your are looking at the Hatteras site, I'll stop repeating here.

BTW, what is your take on my question about the frozen compressor problem on my other unit (in my discussion with Kush on Hatteras).

Thanks.

June 1, 2010
9:45 am
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Hi George~

Yes I have seen your posts over on HOF...Didn't think I needed to post both places...

Since we have verified air flow somewhat... 

Kush is right you are way undercharged at the above figures, and yes...You never want the suction to drop below 58 psi (around 32 degrees)

You should also have enough flood back to keep the compressor below 120 degrees on top (yours is way too hot & will fry that compressor)

You want to do your charging with High fan...Then when done (with a 100 to 120 degree compressor) if your suction starts to go below 58 psi on low fan (freezing) you may need to go into the SMX control programming & raise the low fan speed a bit to keep it above freezing...The SMX does have a de-icing algorithm that cycles the compressor at cabin temps below 70 degrees in cooling mode but you would like to keep the pressure up too.

The key here is cooling that compressor without slugging liquid...You may even get a bit of sweat just around the suction inlet of the compressor itself at times...a bit is ok (but preferably not) and we obviously don't want a cold sweating top...

With your quoted seawater & cabin temps...I might expect around 70-75 psi suction ( 40-44 degree evap) & around 225 to 235 psi head...

Now depending on how scaled up the condenser is...Both could be even higher with the compressor getting enough gas back to cool it....and with the age of your system...This may be what's throwing you off...

I would charge to those pressures and then see where you run...Remembering we don't want to overheat or flood the compressor...

Where ever they end up with a normal temp compressor can answer the question of if it's time to flush the condenser or not...

Steve~

June 1, 2010
9:02 am
reefgeorge
Melbourne, Fl.
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Steve

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).

I lowered the charge to the point where I just barely met the minimum evap delta T of 15 degrees as an experiment and here are the results after 3 hours (cabin started at 93 degrees, external temp 90+):

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

Thanks,

BTW, here is a discussion on the Hatteras forum where I asked the same question (and where I found you(, that gives some more info/opinions/questions:

***************************************************************************************

krush
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Re: Freezing suction line - Today, 12:08 AM

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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
Registered Member Posts: 2
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Re: Freezing suction line - Today, 09:35 AM

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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.

June 1, 2010
6:18 am
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Steve Pooler
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Also George...Have you gotten to & actually removed the filter on evaporator fins themselves ?...

All Cruisair units shipped with a filter there because they never know what the installer will be using for a return grill (filtered or non)

I have found that filter to be like a piece of carpet on units of your's age, and when folks didn't know it was there...

Before I answer your charging/superheat question, lets check that evap filter, and get compressor temp after running for at least half an hour.

Steve~ 

May 31, 2010
7:41 pm
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Steve Pooler
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Ooops…I was on a smartphone too…You may have lost a fan motor…That's really what it seems like…

Steve~

May 31, 2010
12:21 pm
reefgeorge
Melbourne, Fl.
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Steve

I have what appears to be good flow both ceiling grills but i'll check that at the end of the colldown cycle as well. Thanks,

George

May 31, 2010
12:17 pm
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George Some of those overhead units were twin blower. You may have lost a blower motor…

May 31, 2010
12:07 pm
reefgeorge
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I'll also shoot the compressor temp with a heat gun. Sorry about all the edits and extra posts but i am struggling with these posts on a smartphone (no computer acces today).

May 31, 2010
11:47 am
reefgeorge
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This is an installation in a 2002 Cabo which has worked fine since new. I did notice during the last winter that the system started cycling in heat mode before attaining setpoint which would suggest airflow or an overcharged condition. In any event, nothing has changed since the boat was new so there have been no accidental or deliberate changes to the airflow that I know of. To you specific question- it is a salon unit with a single overhead ceiling intake griil and an overhead evaporator with twin duct outputs going to 2 ceiling grills. I will measure the grill surface areas when i get down to the boat today and update you. I am also going to check subcooling to get more info on charge levels. Does increasing charge level to target suction pressures ever straighten this type of thing out or does that just push us to absolute zero superheat and a flooded/dead compressor?

The starting point has been around 90 degree cabin with around 55%humidity. The end point when sh crashes is around 77/40. Pressures during that whole cooldown cycle only vary around 2 saturation degrees downward on the suction line, ending lower.

I'll also check the compressor type.

BTW, the other unit is dead with a locked compressor (since about 6 months ago). I only mention in the event that these issues are related. I suppose the unusual load may play a parr in this. Iwill have some questions about that unit at a later time ("harder" start capacitors, 417/22 conversion, etc.)

May 31, 2010
11:30 am
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Hi George~

I would start with airflow...Can you describe the duct/grill system, or can you remove the duct at the AH (of course without it sucking it's own air back) Then test again ?

Also what kind of return flow do you have...Can you describe it ?...Open flow or ducted ?...What is the grill size ?

What is the cabin temp at startup and what are the pressures then ?

How hot does the compressor get & is it a Tecumseh AK 8515E ?

We are looking for 15 to 18 degrees diff...No more & No less...Your description seems to point to air flow problems which is not at all un-common in marine installations...

Steve~ 

May 31, 2010
10:42 am
reefgeorge
Melbourne, Fl.
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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