Low Low pressure

[JMT]

I am having a nightmare of a problem with a 10 ton R22 A/C charged it with the correct weight of gas, but the low pressure side is only reaching 30psi at idle on run its about 15psi (low pressure switch does not make until 35psi) I have checked the TEV and the filter drier as I presumed one would be blocked or faulty but both are ok. I am new to this so please be gentle any help would be great.

[Yuri B.]

30 psi for R22 at adle corresponds to - 12 C ambient, what is not probably the case.

[Brian_UK]

Silly questions perhaps but... all valves and other dev ices open?

With the unit running try taking pipe temperatures along the system to see if there is a temperature drop somewhere caused by a restriction or blockage.

Also, welcome to the forum.

[frank]

First thing to check with low suction pressures is the airflow over the evaporator. If the indoor unit is not absorbing sufficient heat to evaporate and expand the refrigerant, you will get low suction pressures.
Could be dirty filters or dirty/blocked coil, assuming that the gas charge is correct.

[martinw58]

has the unit got head pressure control on the condenser fans and have checked super heat

[JMT]

Going back to this in a couple of days will check superheat. But what is head pressure?

[martinw58]

the high pressure side of the system the condenser fans are controld by a pressure switch or a fan speed controler

[stufus]

If not a packaged unit and a split system the plate charge may not be sufficient.
Cheers
Stu

[WeNeedUnions]

Has the donk/compressor been converted from a recip to a scroll if it has compare the unit capacity to motor capacity even if the scroll is is 1kw higher these are the symptoms you will get. For example if you have are replacing a 16kw recip for a scroll and your only options are a 15kw or 17kw scroll alot of idiots choose the 17kw and you have the problem of the donks pumping efficiency being to great and you get the symptoms you stated now when it comes to scrolls in this example go the 15kw dont ask me why i cant remember but i had a copeland tech engineer guru explain it to me i cant remember the full tech run down of it but in laymans it had to do with its pumping efficiency and comp ratio of scrolls vs recips they are better even at the same kw rating believe it or not and i have seen the effects of choosing the bigger and smaller. Every time you go the bigger it runs operating pressure like a bag of **** when you choose the smaller it runs like a dream.

[WeNeedUnions]

...and when they are over sized they pump down like a rotary before the pressures even remotely now a cheap nasty fix( i havent done it personally i have always switched the donk) i have seen people do it is to make a small bypass hot gas injection to the the suction line with a little throttling valve to balance it out and give it a better comp ration between suction and discharge and dodgey as it is it does work a guy i know did it and it has not missed a beat for the last 6-7 years or at least he or i am aware of lmao.