Properly charging a system?

[Esoom57]

My buddy (who does HVAC) were installing a new condensing unit for my cousins florist. The old one crapped out on him seized up I beleive. I don't know too much about comercial refrigeration since I work on small vending machine and reach in display cooler units with cappilary lines. =)

AS he is about to charge the system I notice that he's adding alot of refrigerant. I would say about 5-6lbs to a system that not too long ago before the major leak was repaired the other frig tech guy added only 2lbs???

As soon as he turned the compressor on he noticed that the low pressure kept cutting in and out so he added more refrigerant for a total of 7lbs. The guages were reading on the lp just over 0 and the hp just under 100.

Next thing he decides to increase the low pressure control so the comp would stay on. After about 10 minutes gauges are the same reading as before he feels the suction line and says hmmmmm it's not that cold. So, he tells me listen get a condensor fan control that will do the trick. It's cold out here he says and the head pressure is getting way to cool from the fan and climate. So, I understand the CFan controll but I don't understand is why he added that much refrigerant??

My question is this......Did he put too much refrigerant in the system?

Cooler info -

Evap coil runs about10 feet long with no fans.
Hermetic Comp 3/4HP 115V Cope
Refrigerant MP 39
Low Presssure Control

any help would be great....it really seems weird to me he added that much I don't know I'm lost here.

Thanks
Esoom

[Brian_UK]

What is the expansion device?

How long are the pipe runs?

Was the old system running on R12?

More detailed readings of the system are required.

[coolstuf]

If it's a split ac,they normally have capillary expansion devices,that means the system is critically charged,look for charge weight on info plate(split ac normally precharged) . If piperun lenth is inside manufacturers spec, charge only given weight, not more, not less. If piperun is longer/shorter than spec, contact manufacturer. PS,sounds like you will be giving your buddy a hand to change the compressor again, soon.

[Esoom57]

Hey Brian UKL and cool stuff Thank you very much for your replies.

Brian Uk answers :

The expansion device is a thermostatic expansion valve with a cap tube coming out of the top of the diaphram with a bulb at the end. ( I hope this is what you ask for as I don't work with TXV I only work with rinky dink units with cap lines to the evap.

Pipe runs from the compressor unit to the evaporator are about 8 - 10 ft. 3/8 copper to the TXV....then 1/2 to 5/8 copper going to the compressor. The evap is about 10 feet long by 1 1/2 feet wide. Pretty long.

The old system did run on R12. But it has been serviced before by a SOME SHADY ASS mechanic. Reasons why I say shady cuz this piece of garbage told my cousin he was charging the system with R12 when I took a look at his BILL it had said MP-39 and he charged him for R12 price. <---First Leak on the pipe going to the condensor. Then there was another leak about 1 month and a half later. The other mechanic said that one of the shrader valve was missing an oring. (JEEZ I WONDER WHAT HAPPENED TO IT COULDNT HAVE BEEN THAT PIECE OF GRABAGE FROM THE PREVIOUSE SERVICE CALL). So this mechanic charged it with Hot Shot. Sorry I am just venting a little =)

Coolstuff -
The system is a Reach in Display Cooler. I should have had said that from the first time that it is a display refrigerator. The compressor condensing unit didn't come precharge hence the reson why my buddy didn't know how much to charge it with.

Well, I have an update since the last time we charge it. My buddy (HVAC guy) calls me up and told me that he has spoken to a buddy that does refrigeration and told him that the TXV is bad. So, now I have evacuated the system and taken off the TXV. Just to make sure I taped up the ends so that no moisture tries to get in. I'm on my way to the supply house tomorrow Sunday morning to match up the TXV.

I do have another question =)

Doing a quick search I found out that the color on the expansion valve is yellow which stands for R12. I don't know if thats what it means but I'm assuming from some other wbsites.

Now for my question. Since we charged up the system previously with MP-39 aren't you supposed to use an expansion valve that works with MP39 and not the old stuff R12?

Thanks in advance guys. BIG HELP!

Esoom

[nike123]

I think that you have to many buddies and cousins in game and to little qualified technicians for that task.

[nike123]

Doing a quick search I found out that the color on the expansion valve is yellow which stands for R12. I don't know if thats what it means but I'm assuming from some other wbsites.

Probably yes. What is valve make and model?

Now for my question. Since we charged up the system previously with MP-39 aren't you supposed to use an expansion valve that works with MP39 and not the old stuff R12?

MP39 is created to be retrofit for R12 and there is no specialized TXV for MP39. Original valve , if works correctly, does not need replacement, but there is some other issues:
http://refrigerants.dupont.com/Suva/...pdf/h75336.pdf

[Rob123]

Recover the Refrigeran and start again... as a rule of thumb use air on condenser + 15c.Use comparitor to calculate Press/temp and charge to that...
eg Air on condenser 25c +15c =40c R22 @ 40c = 14.3 bar/143 psi (For non critical charge systems)

[Yuri B.]

Apropos ACs being critical to the charge. 7 years ago I saw a split whose compressor was choking with refrigerant - somebody uncompetent must have overcharged it heavily at, probably, some coolish day. The AC system should have been pumping pure liquid in itself. The mechanic I was along with simply let some of the charge out. Fair fire-extinguisher it looked from outside, there is no end to the substance, was my thought (I did not know at that time that it was illegal). After that the AC went to cool, the happy client signed our bill. So, some ACs may be less critical to the overcharge.