zpm

I've got an early 90's rooftop unit that takes 7 pounds of R-22. The system hasn't been working very well so I called out a recomended company. The tech hooks up his gauges and tells me I have less than a pound left. I'm getting 10 degrees of delta-T across the evap coil.

Q1 - Can you make a reasonable estimate of how much refrigerant is in the system based on the pressure gauges?

Q2 - If the system were really that low on refrigerant, would it still be cooling 10 degrees?

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biggles

weighing freon in or taking it out is the only way to find out whats left in a system.if you only had that ONE pound left the machine would of been off on low pressure safty....the compressor would have almost nothing to compress to start the cycle.unless the liquid line is filled it can't make a temperature drop on the evaporator coil when it hits the metering device.you need a good nitro pressure test to 400psi and the leak will find the tech if it is bad.then a solid vacuum and pulling 500/250 microns will back up a tight system to take the new charge.

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beenthere

If youo had less then a pound left, you wouldn't have a 10° temp drop,

He made a guess.

zpm

And then he tried to sell me a new system. I've got no problem getting a new system if I need one, and I may, but giving me obviously bad info seems like a setup.

Should I tell them to come back and charge the system?
How would I know if they actually do it right?

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Plumber101

Almost all techs carry a portable scale.

Have the tech weight the jug of freon in front of you before going on the roof and after he come down from charging it. This will tell you how much freon he put in.

This will keep him honest

beenthere

Not really.

If he has to go on teh roof to charge it.
He could simply blow off a couple pounds from the cylinder, until it says 7 pounds.

I'd simply call another company.

Plumber101

That's true Been

If it were me I'd shimmy up the ol roof with the guy and then ask where the scales are.

Just to prove a point

zpm

I don't think this company is that dishonest. Maybe the Jr. Tech gets a little something for every sale he makes so he stretches the truth, not realizing it might snap back in his face.

I'm more concerned with being able to verify that they put the correct amount of R-22 into the system, whether it be 1 or 5 pounds. Just because a guy has the right tools doesn't mean he knows what he's doing.

I took a look at my actual temp data from last summer from comparable days.

7/23/2008, 16:00
outside 100.82
return 78.01
evap 63.81
delta-t 14.2

6/30/2009, 16:00
outside 101.82
return main 83.30
evap 71.85
delta-t 11.45

I've lost almost 3 degrees of cooling. There's probably a tiny leak, but at this point I'm thinking to tell them just charge it up and screw any leak tests and fixes. This system isn't worth pumping a lot of money into. If/when it bleeds out again I'll look at a new system. Any problems with that plan?

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beenthere

No. They can do a gas n go.

zpm

Resolution:

Talked with the service manager and explained the bad vibes I got from the tech. They sent out another tech this morning to fill er up. Took 2 pounds.

7/2/2009, 4:13 pm
outside 102.09
return 78.01
evap 59.11
delta-t 18.9

Its comfy in the house and the A/C is keeping up and actually cycling.

Interesting how just a few degrees makes such a huge difference.

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beenthere

Amazing what 2 pounds of refrigerant can do.