Newb replacing an old condensing unit

Problems related to residential installations.

Newb replacing an old condensing unit

Postby samboy » Tue Aug 14, 2012 2:02 pm

I recently revovated an old house with all new ductwork, furnace (GMV95/ GCV9 Two-Stage, Variable-Speed Gas Furnace), and spray foam. I decided to keep the old condensing unit since I had replaced the coil 6 months prior to making the decision to completely revovate the house. The condensor is an old Carrier 38CKC048360 (I tried posting a pic with product information I think it's a 4ton 10 seer unit, but I'm not too sure how to tell). Anyway, I think it's starting to give out, and I want to replace the unit rather than troubleshoot the capacitor, fan motor, etc. I am having to push start the fan now whenever we turn the air on. The current unit has never performed well relative to the furnace, and I've gotten an offer from my HVAC guy to install a slightly used 4 ton 12 seer American Standard unit for $800. My HVAC guy installed everything that I have now, and I trust him as much as anyone that I've ever done business with. He works in the commercial business, but does residential on the side over weekends, etc. My only concern is, should I try and find a different replacement in order to achieve maximum performance? My house is 3100 sf with high ceilings 2 zones (upstairs and down), and even when the existing unit was running great, it was hard to keep the house at 75 degrees when the outside temp was in the upper 90s.

I haven't discussed asked for a cost on installing something different, but I'm sure he would do it. I just need to know what is the best move that I can make at this point in terms of performance, effieciency, and compatibility? Would the deal for $800 for a slightly used American Standard unit installed be a good deal assuming that he is willing to back it for a couple of years?

Thanks for taking the time to help with my situation, and please let me know if I've left out any pertinent information.
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- Newb replacing an old condensing unit

Postby Freon » Tue Aug 14, 2012 7:56 pm

"I am having to push start the fan now..." That is definitely a capacitor issue. Please replace it ASAP since it's still summer. Buy an IDENTICAL capacitor as far as microfarads go... mfd. The voltage can be equal to or greater than your capacitor. Pull the disconnect to the condenser and mark the wires before removing them from the old capacitor. Take the old one to an HVAC supply house... about $15 and 10 mins work.

"My only concern is, should I try and find a different replacement in order to achieve maximum performance?" Your indoor coil will limit any efficiency gain from the outdoor condenser. I assume you have a 10 SEER indoor coil (evaporator). So fix your condenser... it's 10 SEER. A 12 SEER condenser will work fine but give you effectively 10 to 11 SEER efficiency.

Fix the condenser capacitor (make sure there's not a start capacitor too... if so check it physically) and clean its coil. You may have many good years ahead of comfort. Change your indoor filters, the biggest reason AC systems are not up to their best.
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