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Testing A/C systems


Robert E Lee
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I got to yesterdays afternoon inspection a bit early, start the outside and a few minutes later the agent and client show up. I bring them up to speed as to what I/ve looked at so far, and discribe the age and size of the A/C compressor and state that because it is in the mid 50's today (and was below freezing last night) that I would not be running the A/C. Suggested they would want to be sure and run it during the final walk thru. Well I go on with the inspection, the agent leaves, and just as I'm finishing up I hear the A/C unit come on...the client has decided to check things out. Well at this point its already running, so I go ahead and take the TD's (unit did seem to be working ok). So what do the rest of you use for a go/no go when turning on the A/C. I tell folks (and this guy) that until we get to where it is 55-60 degrees within the past 24 hours I don't start up A/C units, it has been my understanding that this is also the manufactures recommendation.

Robert E Lee

GENERAL Home Inspections, Inc

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Hi Robert,

Personally, I would have turned it off and told him that he didn't own the house yet and had no right to place any of the home's systems at risk of damage until he did.

I think you should be careful to include in your report a statement at the beginning of the AC portion of the report that you informed the client that you would not be running the A/C due to low temperatures, but that he took it upon himself to start the A/C without your knowledge or permission, therefore relieving your firm of any responsibility for recovery of damages, should it malfunction or otherwise fail now or at any future date.

ONE TEAM - ONE FIGHT!!!

Mike

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I think you have it about right General. I don't have an exact temperature, but if I need to run the heat for comfort I'm probably not going to run the AC behind it.

I've had clients move to turn on items I've decided not to test for liability reasons. If I'm standing there I stop them and remind them that the house still belongs to the seller at that point, and advise that they should have the seller do it. "If the seller turns it on and it breaks, it's the sellers problem. If you turn it on and it breaks, it's your problem." So far that has worked every time.

Brian G.

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AC compressors have a heater at their bases to keep the compressor warm enough to boil off the refrigerant. They compress gas not liquid, and running them cold will damage them.

A compressor MUST have been plugged in for at least 12 hours accompanied by an outdoor temperature above 65F before I test them.

Mike and Konrad have it right.

I would have turned it off immediately and noted it in my report.

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Rob C,

Not all condensers have the crankcase heater.

Inspected a house today for the owner of a large HVAC/mechanical contractor. The first thing he did was turn on the AC, even though the temp was maybe 55 and cold overnight. Both condensers were builder grade, so no crankcase heater. He said it would do no harm.

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A couple of things to keep in mind:

  • As Neal pointed out, not all AC compressors have crankcase heaters. You can see the heaters (or at least the wires leading to the heater) on most models.

If it's been cold out and it's a reciprocating compressor and it has no heater, or if the power's been off for hours, the compressor may slug. This is bad.

If it's a scroll compressor, it's not an issue.

- Jim Katen, Oregon

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Good point Neal, the ones I've run across up here have had heaters. Could be a marketting or regional thing.

There are many variables in compressor design and without the 2 year refrigeration training I use the 12 hours/65F rule.

In conversation with HVAC contractors I've come to realize that the topic is complex and can even trip up an experienced guy.

Speaking for myself I wouldn't want to have to replace a compressor.

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