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Old 04-25-2012, 09:03 AM
 
232 posts, read 396,417 times
Reputation: 155

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As a follow-up, here's the result of the second opinion (Trane certified):

- Expansion valve is functioning properly based on metering
- No known problems with this coil
- Cost for replacing valve (incl. part) $300/not $500 and coil (excl. part) $750/not $1200
- Appears that corners were cut on the installation and that vacuum may not have been sufficient resulting in freeze.
- Strong possibility that the freon leaked over time as a result of installer diagnosing the freeze (no evidence of oily deposits)

Repair company #2 advice: Wait to see if it freezes again, then call. Diagnostic charge: $0/not $149. Of course, we tipped.
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Old 04-25-2012, 11:04 AM
 
Location: Somewhere in northern Alabama
11,763 posts, read 27,361,886 times
Reputation: 14592
Good. ($750 - my guess around $800 {assuming you didn't signal him that price range somehow})

Coil freezes often occur from restrictions (crud) in the coil, which slow and back up the flow of refrigerant, and act like poorly designed expansion valves. A small area of the coil then gets much colder, and condensed water from the air freezes instead of dripping off. Typically, if you watch it happen, you'll see one or more spots start the freeze, and then it expands.

With a heat pump, a quick temporary fix is to put the system into heat mode to melt the ice, then run the system for just a few minutes at a time. Without a heat pump, just run the fan only. Since there is ice, your system won't be cooling any faster than if you had the compressor or scroll running. Once the air starts running warm, you can again run the system for a few minutes at a time.

Running the AC on cold damp days may cause icing a little faster. One other thing that can cause icing is an overly restricted airflow or weak fan. Make sure vents are open and filters changed when they get too loaded. If you can adjust fan speed and have been keeping it low because of the noise, you might reconsider the higher speed.

(The reason I had thought $800 was overhead costs and time management. KB thought low, I thought high. Depending on the area and level of business, either guess is good.)
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Old 04-25-2012, 09:14 PM
 
Location: Florida
316 posts, read 671,506 times
Reputation: 273
Quote:
Originally Posted by K'ledgeBldr View Post
Harry-
When was the last time you actually saw a tech do an evacuation/charge?

I haven't seen a vac pump in yrs. They all use nitrogen to evac now.
Oil usually doesn't leave the system, recovery systems are basically holding tanks (the refrigerant goes back into the system), and driers don't have to be replaced unless the system has been "open" for an extended period of time.
K'ledgeBldr-using a vac pump is SOP by any company who knows what they are doing.Nitrogen is never used as a subsitute for a vacuum pump.Refrigerant in a recovery tank does not go back into a system until it is reclaimed and meets ARI purity standards. Nitrogen is used for leak testing and chemical flushing.Yes old driers should be replaced when the system is opened.
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Old 04-25-2012, 10:39 PM
 
239 posts, read 346,266 times
Reputation: 193
Please never let anyone tell you that a vacuum pump is not required, nitrogen is used during brazing and to purge systems but it is non-condensable and should never remain in the system
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Old 04-27-2012, 03:58 PM
 
232 posts, read 396,417 times
Reputation: 155
Quote:
Originally Posted by harry chickpea View Post
Good. ($750 - my guess around $800 {assuming you didn't signal him that price range somehow})
Harry - you were right on the money. The repairman said that nothing was wrong. So we asked "And if it had been?".

BTW, the cost for an isolation test is $250 - really reasonable compared to replacing random parts in a succession of repair visits.
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Old 04-27-2012, 11:01 PM
 
Location: Johns Creek, GA
6,838 posts, read 21,993,556 times
Reputation: 5359
Quote:
Originally Posted by kevink1955 View Post
...nitrogen is used to purge systems but it is non-condensable and should never remain in the system
"to purge"- Hum, seems someone has forgotten the definition.
And it doesn't remain in the system.
If I said it once, I've...
"Time is money". And the last thing a HVAC contractor wants to do is pay a tech to sit around while a vac pump pulls down a system. A nitrogen purge has been proven time and again to be an excellent alternative to the traditional vac pump.
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