Condenser whistle

[atxtim]

I have a Goodman split unit (GSC130601BC).  The outside condenser runs and cools the house.  However, at the end of a cycle it emits a high pitched whistle.

I thought maybe the valves or external pipes were leaking, but I went outside

and poked around and it sounds like it is coming from the condenser itself.

I had a repair guy come out and he wants to replace the disconnect

(Which looks like I can get one at Lowe's for $10)

 

Charge the system because coolant is low.

Add float switch in closet

Increase air return.

Questions:

0> Does this sound like I have a crack/leak in the condenser?

      Can it be repaired or do I have to replace?

1> Where can I find information on return air sizes?

2> Where can I find information on float switch, is it needed?

Thanks for any help

[dkpd1581]

The loud whistling sound is most likely the pressure differential of the refrigerant gas across the compressor equalizing in the off cycle.  There is generally 150+ pounds per sq inch difference from the inlet and the outlet of the compressor.  The valves are most likely allowing the gas to equalize through them causing the whistle.

To your specific questions:

1. No the noise does not necessarily indicate a crack or leak in the condenser.  Freon and oil used for lubrication of the moving parts in the system mix extremely well.  Wherever the freon goes, the oil follows.  If you suspect a leak or crack as you describe it, look for an oily spray or dark wet residue on the metal surface(s) - a quick non technical way to check.

2.  Return air information is typically derived from scales or charts (most typically a Ductulator - the HVAC guy's fancy slide rule).  It is based upon the size/tonnage of your machine which in your case appears to be a 5 ton unit.  Rules of thumb / generalities go along the lines of 400 CFM per ton of airconditioning.  Therefore you (having 5 tons of cooling) need duct work to accomodate approximately 2,000 CFM.  Factor in the friction rates (drag created by the air moving across the specific materials your duct is made of), equivalent losses created by bends and elbows (more friction) to get that duct back to the unit, and noise considerations (too much air across too small and opening at to great a speed can cause obejctionable noise) will give you an answer. Typically returns are slightly bigger than the supply to reduce noise, vibration, and friction losses - although technically the supply ductwork should equal the return.  Thats the difference in opinions, experience, the book versus the boulevard.

3. The float switch is technically not necessary just as seat belts and helmets are not necessary while driving down the highway.  Can you get away without it (getting a ticket from the nice Officer aside)?  Yes you can get away with it.  However, when something bad happens, the float switch is your safety net and can keep the bad from becoming catastrophic.  My suggestion - Get one.  WWW.URI.COM

[hvacdrd]

[user=50693]atxtim[/user] wrote:

Questions:

0> Does this sound like I have a crack/leak in the condenser?

      Can it be repaired or do I have to replace?

1> Where can I find information on return air sizes?

2> Where can I find information on float switch, is it needed?

0 - No, if the condenser was leaking the unit would not be cooling at all. Since this is the higher pressure side of the system it doesn't take long to lose the complete charge when it leaks at the condenser.

1 - Return air size is based on cfm(volume) and velocity(speed), model number indicates the unit is a 5 ton, at 400-450 cfm/ton return duct should be sized for 2000-2250cfm @ velocity rates of less than 600 fpm(for noise & resistance/friction). Minimum duct size 452 sq. in. is 637fpm. 24" round-  20x25

2 - Likely this "float switch" is for the condensate pump(typically part of the pump), if the pump fails it will not allow the A/C to continue to run(producing condensate & leaking on the floor)

As for the noise, some scroll compressors make a noise when the unit stops as the scroll plate stops the mechanical energy the pressure forces back thru the plates. Other possible sources are internal bypass if running high head pressure.

The charge system because "coolant" is low - based on what numbers? Refrigerant(ie coolant) does not get used up or depleted. The only reason to add would be if it is leaking (requiring leak repair)

[atxtim]

Wow, thanks for the great information from both of you.

Pressure numbers:

Suction side: 57 psi

High side: 170 psi

He also mentioned that the compressor was drawing low current, but does not mention that the compressor could be going bad.

I don't see anything around the lines that would indicate a leak. I do see that my lines do not have insulation completely covering them. There are breaks in the insulation.

Also, he is suggesting the disconnect be replaced. As far as I can tell, all this is is a manual switch to cut power to the unit.

[hvacdrd]

Pressures do not look out of line for mild temperatures. (I'd expect lower current) -Most charging charts for fixed orfice/restrictor are based on 1-indoor wetbulb 2-outdoor air temp 3-superheat - TXV systems are based on subcooling - without that information it is hard to say.

If the service disconnect does not work, has corroded, burned or otherwise damaged terminals then I'd agree. Otherwise I don't see the point.

[atxtim]

Thanks a bunch, you guys probably saved me a bunch of unnecessary repairs.