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View Full Version : Low side too low and high side too high







Greed4Speed
31-10-2012, 08:39 AM
I just repaired a single stage cpu condensing unit (machII), had a crack in the suction line. I replaced the suction line, filter drier, then charged with r404a, system uses a capillary tube as a metering device.

When I run the unit everything seems ok at first, pressures ok, it cools down to -52. After about 4mins the temp starts increasing, also at the same time the low side goes lower and lower until it's in quite a deep vacuum. The high side pressure is also unusually high, starts off high but gets a little higher as the low side goes lower. Also when I switch off the unit the low and high side pressures do not equalize, only after a few hours do they equalize.

I'm suspecting a blockage somewhere, what do you guy's think? I have never seen these symptoms, very unusual for me.

RusBuka
31-10-2012, 11:11 AM
Clogged capillary tube or sunken ...

frozen air
31-10-2012, 02:55 PM
I have had the same issue in the past, found out that the compressor has been replaced and it was one size to big, they had installed a CAJ 2464 Z instead of a CAJ 2446 Z....just something to check.

Tesla
31-10-2012, 09:20 PM
For the blockage check for a cold spot metering device or drier. How did you charge the system by weight or other - it could be overcharged too. Considering it takes time you could have moisture in the system causing the blockage.

Brian_UK
31-10-2012, 10:31 PM
As mentioned above, what level of vacuum did you achieve before recharging as it sounds like an ice block forming at a restriction.

chillerman2006
31-10-2012, 11:25 PM
Hi Greed

blockage should pull 30inch vac, wrong compressor will not pull that low if there is gas flow

R's chillerman

monkey spanners
31-10-2012, 11:44 PM
Could it be oil problems? -60C evap temp is very low.

Greed4Speed
01-11-2012, 12:09 AM
Clogged capillary tube or sunken ...
Thanks for your suggestion, much appreciated.

I have had the same issue in the past, found out that the compressor has been replaced and it was one size to big, they had installed a CAJ 2464 Z instead of a CAJ 2446 Z....just something to check.
The compressor is the original, what came with the unit from the manufacturer, thanks.

For the blockage check for a cold spot metering device or drier. How did you charge the system by weight or other - it could be overcharged too. Considering it takes time you could have moisture in the system causing the blockage.

I charged by weight, put about 300g of r404a. Moisture is a deffinate possibility, now that I think about it, I rushed the vacuuming as my new vacuum pump (robinair) seemed to be strange, 10mins into the vacuuming I noticed a strange burning smell coming from the pump, was sort of a burnt rubber smell, I looked at it's sight glass and noticed the oil change had a cloudy/milky appearance. I have since changed the oil and tested the pump on another unit, it pulled a fairly decent cucuum or at least I think it did. The oil is still slightly cloudy, do you think the pump is faulty/damaged?


As mentioned above, what level of vacuum did you achieve before recharging as it sounds like an ice block forming at a restriction. As above, you have a very good point, thanks.


Hi Greed

blockage should pull 30inch vac, wrong compressor will not pull that low if there is gas flow

Not sure if I understand what you are saying, please explain in another way.

R's chillerman


Could it be oil problems? -60C evap temp is very low.

I have another unit which has the same evap temps, that one runs very well.




Thanks everyone, wish I joined this forum sooner, you are a great bunch of guy's.:)

chillerman2006
01-11-2012, 12:14 AM
Hi Greed

what I am saying is if your low side gauge goes right to the bottom of the vacuum scale it is blocked

it will not go to the bottom of scale with over sized compressor

R's chillerman

Greed4Speed
01-11-2012, 12:21 AM
Hi Greed

what I am saying is if your low side gauge goes right to the bottom of the vacuum scale it is blocked

it will not go to the bottom of scale with over sized compressor

R's chillerman

I see, thanks.

RusBuka
01-11-2012, 05:28 AM
Cooling system for processors usually run by ***** 3 \ 4 of the necessary, and then start to add 15-20 grams every 10-15 minutes at full load. Just pick a capillary tube under the evaporator is very difficult.)))

Greed4Speed
01-11-2012, 08:32 AM
Cooling system for processors usually run by ***** 3 \ 4 of the necessary, and then start to add 15-20 grams every 10-15 minutes at full load. Just pick a capillary tube under the evaporator is very difficult.)))

I understand partly what you are saying, thanks for the suggestion. Don't know what you mean about the capillary tube.




***UPDATE***
I have just started vacuuming the system, this time I have used another pump and it has also turned the oil cloudy.
Can I assume that this is caused by the system being "really wet"?? I remember reading somewhere that some engineers sometimes have to change the oil in their pumps several times if the system is really wet, what do you guy's think?

Tesla
01-11-2012, 10:03 AM
If your pump oil is cloudy it needs to be changed and indicates moisture in system. On this small system you should be measuring the vacuum level at well below 500 microns and holding for some time (to indicate/confirm no moisture in system and no leaks). The capillary may need changing as well as the drier.
To check if your pump is good enough put a vac stat straight on it and anything 25 micros or below is good, above 50 micros and the pump is going to do stuff all.

RusBuka
01-11-2012, 05:25 PM
I understand partly what you are saying, thanks for the suggestion. Don't know what you mean about the capillary tube.

***UPDATE***
I have just started vacuuming the system, this time I have used another pump and it has also turned the oil cloudy.
Can I assume that this is caused by the system being "really wet"?? I remember reading somewhere that some engineers sometimes have to change the oil in their pumps several times if the system is really wet, what do you guy's think?

Length of capillary tube is very difficult to calculate. The system is controlled by the amount of *****.

Greed4Speed
02-11-2012, 10:28 AM
Sorted, was a moisture problem as I suspected, should of known better. I vacuumed the system again, gave it a much deeper seeing to this time. My vacuum pump is ok now, no more cloudy oil, no burning smell. System running well now.

Thanks guy's

Brian_UK
02-11-2012, 11:06 PM
It all comes down to the old expressions - "Just suck it and see" :)

The MG Pony
19-03-2013, 07:08 PM
And a tip on using vacuum pumps, warm it up befor you start using it on a system, let it run in a closed off possition till it is hot to the touch, this ensures a lower moisture build up in the oil.