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New HVAC not blowing cold enough… what are the common causes?

John Sexton | Posted in Mechanicals on

I have just had a second new HVAC unit installed. A Trane xr17 condenser and s9v2 furnace. it is installed in my conditioned crawlspace, and I have an identical setup in my foam encapsulated attic.

I am measuring the air at the supplies and returns, and the new install from the unit in my crawl is measuring 65-68 degree air. This is obviously higher than it should be. The upstairs unit measures around 55-57 degree air, and even it was colder a few weeks ago when I measured, as it was around 50 degrees. What kind of things could be wrong that would be making the unit, especially the downstairs, blow hotter air than it should. It is about 82 degrees and 50% humidity outside right now, if that matters. It is 72 degrees and 50% humidity in the crawlspace.

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  1. Steve Knapp CZ 3A Georgia | | #1

    I had a issue recently with my three-year old Carrier unit. The service tech speculated that the initial charge was not handled correctly. The line was allowed to overheat during the startup process, and the heat damaged the gasket in the end cap. The damaged gasket allowed refrigerant to leak out, starving the system and causing it to underperform.

    In any case, you should have the contractor visit and check the system.

  2. Expert Member
    Dana Dorsett | | #2

    Loss of refrigerant is one well known cause of symptoms like that. If it was 50F exit air at the supply register at the same air handler speed a few weeks and it's now 65F-68F, it's not really cooling much, is it? The entering air at the return register is what, 72-75F? Most systems will have at least a 15-25F delta between return air an supply air.

    Lower flow due to icing up on the coils can also have that effect on supply air exit temperatures, but that's also a symptom of improper refrigerant charge, or improper air handler speed setting.

    Or there's a chance it could be just fine. The XR17 is also a 2-stage- it could be that you measured the temps in high-stage at one time, and at low stage another. Can you tell by the blower speed when it's shifting up? (I haven't read the manual on it, but you should.)

  3. John Sexton | | #3

    Yeah I have measured in all stages... the installer is coming out today to troubleshoot. HOpefully they diagnose it correctly and fix it.

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