Printable View
I've lost what to do next. please help me!
Temperature doesn't go down at all. I found the data as under.
over 15 year old walk-in cooler unit.
compressor: AH7480A
u/c : 6000 btu, air defrost model
gas : unknown( must be MP39 or R409a)
suction : 31 psi, 81.4F
discharge: 195 psi, 190F
condenser dT: 24F ( 81/105F)
compressor sh : 45F(estimation)
subcooling : 13F (receiver out : 107.5F)
condenser TD: 40F
evaporator dT: 2 F (63/65F)
Sight glass : clear
compressor amperage: 6.9 ~ 7.2A
Thanks
That's about a 40-degree evap split, and compressor superheat is high. What's the superheat at the evap outlet? If evaporator superheat is high, the coil is starved, in which case it won't cool effectively.
As per Compressor Model, if its Tecumseh, it should have R12 refrigerant. Probably someone charged the wrong replacement refrigerant. Assuming it has the correct refrigerant, suction pressure should be lower around 20 psig.
Shut off the liquid line and see if compressor pulls a vacuum. If the suction gauge shows a slow or prolonged reduction in pressure, you might have compressor valve trouble.
It has worked very charm until I have replaced condenser fan motor. A week later after changing condenser fan motor with new one, the customer complained about the temperature and I found the working condition as above thread.
.
Out of interest, did you check the system after the cond motor was replaced?
I ask because R409 can break down at high temperatures (such as a blocked cond
or faulty cond motor) and if the refrigerant is "thermally decomposed" it will
never respond the way it was meant to.
In such extreme cases the only option is to pull the refrigerant out and replace
it with brand new virgin refrigerant.
Regards
Rob
.
Does the new fan motor turn in the same direction as the old one?
If it is running backwards you will not get sufficient airflow across the condenser resulting in poor performance similar to what you are describing
To: Rob white
I did not check the system after replacing the motor, only received complain a week later.
To: Frank
The motor was same spec. and it worked fine and same direction, no direction issue at all. The condenser dT was 24F.
Thanks.
This statement leads me to think it has something to do with the fan motorQuote:
Originally Posted by jayryu
Hi jayryu
As suggested by Rob there could be a problem with the refrigerant. Shut the system down, isolate the condensing unit from the evap and let it reach ambient temp then read the static pressure. If you think it is R409A the pressure should match a PT chart for the ambient temp, if not I would replace the refrigerant.
You say the discharge temp is 195 psi this is a condensing temp of about 55oC (131oF) where are you getting 190oF from?. What is the ambient temp? If you are running with this discharge temp and the ambient is nowhere near 40oC the as Frank suggested there could be a problem with the fan. Is the speed the same as the old one? Is the condenser blocked?
Have you checked the efficiency of the compressor as Mike suggested?
Regards
Paul
Me to,met another engineer used the term loosely who told me a story he changed a condenser motor because it was noisey then the compressor failed he changed it the next day that failed he replaced it again still had problems then he changed the evap still having issues then he realised he had fitted the wrong wattage cond motor should have been 35 watts but he had fitted a 16! When he fitted the correct one hey presto everything was fine!!,so check that motor.
The consenser fan motor I replaced is exactly same spec. of Tecumseh original part. I think motor is fine. Discharge pressure was 195psi and temp. 190F was measured from compressor discharge tube. It looks too high and bothers me most. I have tried vacuum test for compressor, it keeps -15 cmhg. I think it is not good enough but I also thought the compressor inefficency is not the issue this time due to my past experience. I am too busy to visit the job site recently. it is too far from my area 1hr half~ 2 hrs drive one way.
Is this a TX, or capillary tube feed?
Going to need the room and ambient temperatures for that day you wrote down your observations.:)
The condenser fan motor failure might seem to be the original and only fault but the follow on effects from a dead condenser fan motor tend to bite you on the ass if you don't take the time to observe the kit's performance after repairs.
Just sayin.....
Paul Z on post # 10 has a valid point questioning op's pressure and temperatures.
It is txv. Ambient was 81F, room temp(box) was 65F. There is one more symptom: evap. icing goes to compressor suction tube. When I wrote 1st thread the data was 1 hour after melting the ice build up completely.
What you mean "op" mike?
Frosting all the way back to the compressor indicates insufficient heat absorption in the evaporator, effectively turning the suction line into an extra part of the evaporator.
Check all evaporator fans for correct operation, check coil is clean & free of frost/ice.
If that's all ok, check the TEV superheat.
From your post it seems to me that there's more faults than the original condenser fan here.
First post said compressor superheat is 45F. If that's the case, it's not frosting back. Which is it?
my first observation data was just after the defrosting all the ice built up.
I have visited the job site again and found the box temperature was around 40 ~ 45F and condensing unit works continuously only making box temperature almost no change. checked compressor efficiency again and found not good enough. There was air defrost timer installed and malfunctioning. In summer time, there has been alway ice build-up everyday the owner said. So I concluded it is compressor inefficency issue. But the owner do not want to replace the compressor and want to use it as it is.
Thanks to every technicien and guru.
Well...there is far more to this story that started with a faulty condenser fan motor. Freezer G said that in a previous post.
(By the way, OP means Original Post or poster....The person who started this discussion.)
Aaaand you can't jump to a decision if you can't prove it.:)
Some rooms require a specific defrost intervention due to heavy loads, or constant air change loads with random door openings. See if the door seal is intact.
I add some data from recent observation as follows.
evap air in/out temp: 43.8/39.3
condenser in/out temp: 83.5/101.5
suction : 22psi/78.7F
receiver out: 175psi/101.4F
compressor out temp: 189F
evap out tube temp: 42.5
suction sh : 52.7
evap sh: 18.5
receiver out sc : 23
All the data was estimated as R409a
Does Canada still use Deg F & PSI? 99.9% of people on this site have to convert it to Deg C & kpa or bar!Quote:
Originally Posted by jayryu
Ranger 1. I've been using this site: https://www.google.com.au/url?sa=t&r...KN2v736pBDfAEQ
During my early education years....the Metric system was introduced and it saved me from a sh#T load of mind boggling measurements.
However...some imperial measurements were hammered in and cannot be forgotten. Miles/gallon...PSI...cubic inch....5280 feet to a mile etc.
When someone mentions degrees F that doesn't include 32F, 212F, or -40 F....then i'm off to the above link. :off topic:
No worries Mike I use the Danfoss app for any conversion.Quote:
Originally Posted by mikeref
I think sometimes people possibly even change metric to imperial for the sake of a few.
Canada has been metric for quite awhile too.
Apart from the US I would say not many use it, maybe I'm wrong?
No drama Ranger 1.:) Only a few countries still use Fahrenheit.
These...and i quote: Fahrenheit is used in the Bahamas, Belize, the Cayman Islands, Palau, and the United States and associated territories (Puerto Rico, Guam and the U.S. Virgin Islands) for everyday applications. For example, U.S. weather forecasts, food cooking, and freezing temperatures are typically given in degrees Fahrenheit. ( From Wikipedia.)
Hi Mike
The formula you were trying to remember is F - 32 = 9/5 C, some things you never forget, now I have the app on my phone. Wish I had a smart phone 35 years ago.
When I first started I was using PSI and oF but quickly changed to KPA and oC much easier.
Paul
G'day PaulZ. The formula looks familiar.
I believe it might work if degrees F, minus 32 multiplied by 5/9. (click on the picture. Currently re-testing the formula on my basic calculator.)
I see what you did there Paul. If you only use 32 F as a starting point, your formula works.
However, -40 F minus 32...multiplied by 5 and divided by 9 = -40 C :)
:off topic: Again.
The other quick way is C to F Cx2 +30 (correct formula Cx 1.8 + 32)
F to C -30 off divide by 2 (-32 divide by 1.8)
I seem to remember the divide by 5 and multiply by 8 + 32 or multiply by 5 and divide by 8 -32 formula but never seem to work out which way round it needs to be :p