# "Reduced" cooling - interpreting head/suction numbers.



## bob_cntrctr (Jun 21, 2011)

Gentlemen,

Popped over from the parent site, Contractor Talk, where I usually hang out.

I manage a small (~5,000 sq ft, 2 commercial & 4 residential units) mixed residential/commercial building that seems to have an hvac issue.

AC's not cooling as well as it used to. The air out of the vents is cool, but not cold like it used to be. 

Blower blows just fine. A/C unit's fan runs fine. Outdoor unit has had fins cleaned. The suction line feels cool to the touch, but not "cold", and the head line is quite warm - hot, but not too hot to touch.

So I called in an hvac tech who put his pressure guages on the head and suction. 250 psi and 60 psi. 3-ton unit - quite old - probably 15 years I'm sorry, I don't know the refrigerant, but I know it's been recharged several times already (and seals replaced).

So the tech says it's very obvious. At 60 and 250 there's no question - the head should be no more than three times the suction, therefore there's a blockage in the line which must in turn mean the compressor is dying and spitting carbon into the line, blocking the exchanger. It all has to come out and be replaced with an entire new system. This was stated with no more investigation than checking those two numbers.

So, my question: is it really that cut and dry? Or should I be getting another tech in who'll investigate a little deeper?

Thanks.


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## kartheekus (Jun 12, 2011)

*reply*

Dear Friend, You find out the tonnage (total and you have not mentioned in your post) See the condition of condenser. If it is not properly cleaned, 
if it is charged with excess gas, filters proper cleaning evaporator cleaning,
leakages in the cooling area etc and mainly non condensable gas.
this will help you. generally 100-125 SqFt area will be taken for 1 ton.


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## Vaporx (Jun 29, 2011)

bob_cntrctr said:


> Gentlemen,
> 
> So, my question: is it really that cut and dry?


No, it's not. In order to interpret the pressures, one would need to know the indoor and outdoor temps, superheat / subcooling values and type of metering device feeding the indoor coil (fixed or TXV), at a minimum. 

I could make a guess, based on the information you provided but it wouldn't be "the compressor is dying, spitting out carbon" :blink: .


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## refermadness (Jun 23, 2011)

Sounds like he wants to sell you new equipment instead of investing time into fixing the problem. There could be other issues with the system, but if comp. is dying you could allways replace it instead of buying all brand new. Time for a second opinion.


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## artco (Oct 3, 2010)

What was the outside temperature the day he checked the pressures?
I would try to clean the condenser again and use a good biodegradeable condenser coil cleaner. The check the pressures again. 250 head, if it was in the 80's out does not sound high. 60 pounds suction sounds low.

The system may be low on refrigerant if R-22


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