Suction line frosting??

ChrisJ

I'm a homeowner not a pro and this isn't even my system but I do rely on it to keep me cool at work.



My office is cooled by a central air system which was just repaired last year due to compressor failure. They installed a new compressor, flushed the system and installed a drier\filter on the suction line. I believe its filled with R-22 and has a TXV.



I've been running the system as our building has no windows that open and its been upwards of 80F in my office even though its been cool outside. Its around 70F outside right now and the system ran most of the day. I just noticed frost on the suction line outside all the way to the compressor.



This is the second time I noticed this and its got me concerned. If I recall the evaporator should never run cool enough to frost and you should have a certain amount of superheat to ensure no liquid goes to the compressor? Refrigeration is a hobby of mine, but as many know being book smart is kinda useless when it comes to the real world.



Is it time to call a pro or should I wait until we see some warmer days? I'd hate to waste the guy who repaired it last years time for nothing.

Techman

Frosting

I would be worried, alot! What kind of AC unit do you have? Is it just like a home AC? The suction  press should never go below 32*f  which is 58psig for r22. Does the condensor fan motor cycle on and off? The hi side press should not go below 180psig (r22) which is equal to 95* condensing temp.Call for service. Dirty air filters cause frosting.  80* indoor temp should be hi enough to not frost. If the freon temp is 32* (58psig) then adding 10* of superheat should make the suction line 42* ,not frosting. If the hi side press is low it causes the lowside press to be lower also.

ChrisJ

Style

Yeah the building has 5 units that are just like normal residential units.

The air filter isn't new but I highly doubt its restricting enough to cause this.





On another note, what would you say the safest LOW ambient temp is to run a system like this without a crankcase heater, 60F?

Techman

Crankcase heater.

If the ambient temp is 100* and the AC unit is off ,so that the freon and the oil in the crankcase are the same temp, "refrigerant migration" takes place. A CCH will keep the oil warmer than the freon in the system so that migration does not take place. As far as the oil getting thicker (viscosity) the CCH will help that also. ,but it has to get very cold outside before the oil gets too thick from the  ambient temp.

ChrisJ

Really?

I thought migration was only an issue at lower ambient temps?

It sounds like a CCH is always a benefit then if ambient is cooler than the indoor temp? If its 100F outside but 110F inside, its still going to happen without a heater?

Rich_L

Frosting Suction Line

Number one cause I run across in this situation is restricted airflow. Check the filter and be sure the blower is operating properly. Are there many diffusers closed down? This (frosting of the suction line) can also be caused by a low load in the space or a bad TXV. Did the system work OK last year after the compressor was replaced? In answer to your last question, this system should be fine to run at 70 degrees and would likely run OK down to 60 or so. 60 would be a little chilly. If you need it to run when it's cooler outside you could add some simple low ambient controls to the condenser.

ChrisJ

Restriction

Hi Rich, thanks for responding.



All registers are open and airflow seems pretty good. From what I recall the system cooled well last year after the repair. Maybe I'm wrong but it seems like it wasn't doing well before I shut it down.

Techman

CCH

Refrigerant migrates to the cold also. Refrigerant migrates to the oil under certain conditions, completely filling up the oil w/freon, then as more freon enters the oil and the oil becomes "saturated" , as even more freon enters the oil a "puddle" of liquid freon gathers under the oil ,raising the level of the oil in the crankcase. When the comp starts the freon under and in the oil tries to get into the piston, forcing the liquid oil into a piston that is designed for vapor only. That is not good.

unclejohn

How long

Is the piping run? I think 70* outdoor is a little low to run a A/C unit all day long with out any low ambient controls. Does this unit serve only your office or others as well? Never assume the filters is clean, never.

ChrisJ

Lines

The lines are probably around 40 feet long. I do remember them being run a way that was less than preferred just to keep them inside the building.



Unit does my office and one other area. We will be changing the filter today.



I'm curious, what is included with low ambient controls?

unclejohn

Normally a

Pressure control to cycle the condenser fan is enough for your issue. I doubt you will run the unit over night during cooler weather. Hard start is also a good idea. Another  way is whats called a motor master control which slows down the fan instead of a on off type but they are much more expensive. Is it possible the people in the other area are cold and shut their air flow off? You could have up to a 4-5# pressure drop in 40 ' of line. Which means your coil could be clear but your lines at the compressor frosted. Was it frost or ice.

unclejohn

Refrigerant

Will go to where the pressure is lowest. Usually the coldest spot.

ChrisJ

Frost

It was definitely frost. I'm sure all vents are wide open as I walk by them throughout the day.

Techman

Frosting.

ChrisJ. Look at it this way.On steam you use the proper pressure gauge to give you the best posible "reading"  to set your proper Vaporstat , not some 0-30psig  thing. With AC the proper suction and hiside press readings( + ambient + indoor temp ) will give you a starting place , to point you in a particular direction to start your troubleshooting.Don't wait till the warm weather gets here ,you may have lost your symptons.

JStar

AC

Chris,



I do air conditioning, too.

Techman

Frosting

at the comp,but no frost at the evap coil. I may be wrong,but, my thinking is this. A R22 AC operating at the lowest possible evap temp of 32*f , ,then add 10* for the TXV SuperHeat ,that makes the suction line 42* at the outlet of the evap coil, then 40' away the suction line at the cond unit/comp the SH has to be even higher. Now at/around 32* to 42* a 5 lb press drop ( under sized suction line) is equal to a 4* temp drop. So my math does not add up .

ChrisJ, was the suction line insulated?

ChrisJ

Joe

Hi Joe I know and believe me if it was mine you'd be the one doing the work. In fact if I ever get to the point where I can afford mini splits at home you'll be doing them. My boss has a guy he has used for many many years and he does good work so no reason for him to change.





The suction line is insulated and I noticed Friday they had installed a sight glass on it. I noticed quite a bit of bubbles going through it after an hour of running.

Techman

frosting

A sight glass? Who in their right mind would stoop so low as to put in a sight glass!? LOLLOL. DON'T TAZE ME BRO'S!! Was there a Moisture Indicator as part of that SG? The MI will be a "colored" disk ,some are green/yellow some are dark navy blue/pinkish and other colors.With a heavily frosted evap coil and suction line( there HAS to be heavy frost if the insulated suction line is frosted), bubbling is a normal byproduct  of that frost. A lousy byproduct! Under NO circumstance should there be any "activity" in a SG/MI in a properly " running " AC system.

ChrisJ

Moisture

I did notice the cap showed I think green and yellow. The glass it self I think was yellow tinted but I didn't notice anything weird other than the bubbles.



BTW when I checked for bubbles the line was NOT frosted and was actually barely cool As I said previously though the system isn't cooling very well either.

Techman

Moisture Indicator

Well, there's one for the books! The green is what that disk is supposed to be.Light green and you have a little too much moisture floating around the system That NASTY YELLOW shows  there is A LOT of moisture floating around the system. That yellow also means the F/D are used up and MUST be replaced. Find out if you can have the AC co test for ACID-Hydrofluric-Hydrochloric- Oleyic-any or all of those acids will kill the new comp.If there is no acid present,just hang on for a few more weeks of use and there will be with that moisture thats in the system.Those bubbles are not supposed to be there.Once a MI is installed it may/maynot take upto 24 hrs of running time to show its true color.

unclejohn

Why would

You assume 10*f super heat when the system is not performing properly?

unclejohn

Wel I beg

To differ. A properly charged and running A/C system with no low ambient control running at out door temps at 70* F or below will most definitley have bubbles in the SG.

Techman

Bubbling in LL

unclejohn , I mentioned minimum head press and 95* cond temp and a "properly running" system from the begining of this thread. I have also said that TXV 's require a "full LL at the TXV" under all operating conditions , so , these bubbles in the SG are NOT supposed to be there in a properly running system.Some residential mfrgs say their unit should operate down to 65-55* ambient. In another thread called "subcooling" , I also said that a properly charged unit at one temp will be low on freon when operating at a lower ambient due to "the shrinkage factor".

 Most TXV for residential units are set for 10-12* SH and the TXV will try to keep that 10-12*, and no frost at the evap means a temp of at least 32* , plus whatever SH the TXV is producing plus another SH thru the suction line.

 ChrisJ can you get the Mfrg and MN#

Rich_L

Sight Glass

Chris, you stated: "The suction line is insulated and I noticed Friday they had installed a sight glass on it. I noticed quite a bit of bubbles going through it after an hour of running."



I'm not sure how familiar you are with the proper terminology but you're saying there's a sight glass on the suction line, and it's the insulated line that's frosting? The suction line should be the larger line that should be insulated and running very cool to the touch ("normal" conditions) and the liquid line should be the smaller diameter line that generally runs warmer to the touch.



I just want to be sure we're talking about proper lines here. If there genuinely is a sight glass on the suction line (which would be very unusual) there should be LOTS of bubbles in there, though still no indication of moisture! Thanks

ChrisJ

Oops

Hi Rich,



I worded that sentence very poorly, I'm sorry.

The suction line is insulated and they installed a sight glass on the liquid line. For some reason when I typed that I was thinking "they installed a sight glass on the system" and messed it all up. As I said earlier refrigeration is a hobby of mine but I've never really done much with it as far as central air systems. I own two gauge sets and have worked on automotive systems but when it comes to this stuff my hands don't belong on it in my opinion.



I just went out and double checked the color of the sight glass and all I see is it looks like its copper lined or the housing is made from copper with a post in the middle and the liquid looks clear. The cap for it does show yellow and green where green is marked dry but I don't see green or yellow in the glass.





At this point it sounds like something is definitely wrong so we're going to have the installer come have a look at it.

Techman

C.C.H.

Just ran across a Carrier unit ,the C.C.H.is disabled at 78*f.Humgph!!!!!

Rich_L

No Worries Chris!

No apology necessary either! I just wanted to be sure there wasn't something really strange going on there. Have you had your service guy back yet? I've helped our techs over the phone before but there's nothing like being right in front of the unit hearing and feeling whats going on. Good luck to you.



BTW, the style of sight glass you're describing would (should) have a material on the end of the "post" you described that would react to moisture in the system. That's where you should be seeing green, yellow, or somewhere in between.

ChrisJ

Yep

Hi Rich,



He came out a few days ago and added 2 pounds of gas to the system. The post I beleive could look green, hard to say. It does not look yellow that is for sure.



The system ran beautiful all week with no sign of frosting anymore and much better cooling. He said it may have a really slow leak, but I honestly suspect his tech didn't add enough refrigerant last year when he replaced the compressor. I have a feeling he didn't realize it had 40-70 feet worth of lineset but who knows.



Speaking of frost, I ran my 2nd Monitor top last weekend and am proud to say it doesn't have a problem with non-condensibles like I originally thought. This is a 1934 methyl formate machine that uses a high side float to regulate refrigerant flow. My 1933 unit works beautifully as well.   Another interesting fact is the Monitor top fridges all had crank case heaters or as they called it "an oil conditioner".



See picture.