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DIYPhilip 02-02-2010 12:59 PM

Need 2nd opinion - Replace Heat Pump?
 
Unit: 10yr old (2000) Bryant model 661CJX0048 4T split heat pump. 10SEER, 7.2HSPF. Several small component failures over the years such as condenser start cap, blower motor (bearings), thermostat & control board, all replaced by pro's except blower which I replaced.

House: 10yr old 2400sq.ft. All electric, gas unavailable. 1 story with bonus and unheated/unfinished basement. Located in Atl, Ga. Dust and frequent filter replacement is a big problem for this house.

Background: We have been plagued with high AC bills ($550+) for several years, and suspected something was wrong. Winter's aren't that bad ($330). But service calls for periodic problems (see above) indicated no major problems with the system. Three weeks ago outside temps hit 14*F and the system struggled to keep 68*F (not bad IMHO), a week later it struggled to keep 68*F at 34*F. Two days ago, it struggled all day to move from 65 to 68 with 50* outside temps. Called in a tech.

1st effort: Low temp rise across coil (14-15*). Inspection revealed a layer of lint and dust resembling a coffee filter on the coils leading faces. Cleaned coil. Doesn't explain sudden failure, but it was badly needed. Temp rise *dropped* to 12*. Time to keep looking.

2nd effort: (Note: I'm an an engineer/technician by trade, but not in HVAC or mechanical systems. As such, I am regurgitating what I saw/heard and understood, but the details may not be 100% accurate). L & H pressures close but not right. Typical adjustments do not correct problem. Added freon, tweaked liquid valve, etc. Also L->H pressures equalize too fast on system shutdown. Suspect reversing valve. Tried cycling heating/cooling to unstick RV. No joy. Compressor is drawing 9-10A, RLA specs 24.5A. Suspect RB is leaking/bypassing and causing the compressor to short cycle.

Final diagnosis: Recommendation - Replace compressor/entire unit.

I'd love to hear anyone else's thoughts. The tech was knowledgeable, worked diligently (3+ hrs) to find the root problem, consulted other more experienced techs for a sanity check,and in the end his diagnosis seems appropriate. I just have a hard time spending $3-4K to replace a unit that (at this moment) is running and keeping my house at 73*. On the other hand with our high energy bills and the tax credit, should I just bite the bullet and install a new 16SEER/8.6HSFP unit now?

Philip

Note: I re-checked the running load this morning and temp rise and they are 10A (whole unit incl fan) and 14*F respectively. Outside temp is 48*, inside temp is 73*

H. Phillips 02-02-2010 01:13 PM

Rule of thumb is to keep the unit for at least 15 years. If the compressor blows at 14 years then change it and replace on next major outage. If it does so at 16 years then replace the entire unit. I have seen them last well past 20 years. A stuck or bad reversing valve is not uncommon, you will replace fans, contactors, and other relays over the years. Same as with a new unit, as soon as the warranty runs out. The compressor should last another 5 years. I would have him replace the reversing valve. Yes a higher efficiency unit would be nice but the savings on the bill will take a long time to pay for a new unit.

DIYPhilip 02-02-2010 02:15 PM

Quote:

Originally Posted by H. Phillips (Post 393438)
Rule of thumb is to keep the unit for at least 15 years. If the compressor blows at 14 years then change it and replace on next major outage. If it does so at 16 years then replace the entire unit. I have seen them last well past 20 years.

Good advice. My tech told me that the cost differential between a new unit and a new compressor wasn't that big, and given the age/inefficiency of my existing unit he would recommend a new one.

Quote:

Originally Posted by H. Phillips (Post 393438)
A stuck or bad reversing valve is not uncommon, you will replace fans, contactors, and other relays over the years. Same as with a new unit, as soon as the warranty runs out. The compressor should last another 5 years. I would have him replace the reversing valve. Yes a higher efficiency unit would be nice but the savings on the bill will take a long time to pay for a new unit.

I must have misunderstood. I understood the RV was inside the compressor. You post seems to indicate it's not. I'm sorry if I added confusion. His final diagnosis was that the compressor itself was leaking internally and needed to be replaced. I'll get a quote on just a compressor. I know a failing compressor on other systems often puts debris in the lines. Is the same true? Any precautions I need make sure get done?

H. Phillips 02-02-2010 02:54 PM

Quote:

Originally Posted by DIYPhilip (Post 393479)
Good advice. My tech told me that the cost differential between a new unit and a new compressor wasn't that big, and given the age/inefficiency of my existing unit he would recommend a new one.



I must have misunderstood. I understood the RV was inside the compressor. You post seems to indicate it's not. I'm sorry if I added confusion. His final diagnosis was that the compressor itself was leaking internally and needed to be replaced. I'll get a quote on just a compressor. I know a failing compressor on other systems often puts debris in the lines. Is the same true? Any precautions I need make sure get done?

The reversing valve is not internal to the compressor, it switch's flow to the inside and outside unit to air condition or heat the space. Poor compressor rings would have a similar effect to a leaking RV valve, but since you have a heat pump and he mentioned the RV then he is possibly trying to increase his profit. I would get a second opinion.

http://en.wikipedia.org/wiki/Reversing_valve

beenthere 02-02-2010 04:23 PM

Philip:

The outdoor unit is called the condenser, or heat pump in your case.
The compressor is in the outdoor unit, and the RV is a separate part from the compressor in the out door unit.

As far as equalizing too fast. It could be your thermostat causing that. Depending on what the thermostat does with the RV's control voltage after a call for heat. Some energize it, which then throws the RV to cooling mode with your heat pump. And causes the pressures to equalize very quickly.

When the low and high pressures(charge shouldn't be checked by pressure alone) are close but not right. Its not a problem with the compressor.

Since the indoor coil was so dirty. Did he clean the outdoor coil? The outdoor unitl moves more then twice as much air then the indoor unit. While your indoor supposedly is moving 1600 CFM. Your outdoor is moving 3200 to 3800 CFM.

Might want to clean the outdoor coil. And then you might also be over charged if he added refrigerant.

As to replacing the unit. Before you do that. You might want to find out how undersized your duct work is. This is probably causing a lot of your high bills problem.
Don't fall for the "well the ductulator says at .1" the duct is moving 1600 CFM".
The ductulator is a pressure loss slide chart. Not a how much pressure is in the duct ductulator.

Ask then to check by static pressure in the duct system. Or by temp rise using the electric strip heaters.
A new 16SEER won't much better if your duct system is too undersized.


PS: Your house may only need 3 or 3.5 tons. Might want a load calc done to find out.

Marty S. 02-02-2010 05:30 PM

There is a pressure bypass valve in the compressor as a last ditch attempt to save it on a gross over pressure situation. A dirty indoor coil like you had will greatly increase the head pressure in heating and very well could have caused that valve to stick partially open. Had the same thing happen on a 2 year old goodman unit last summer.

beenthere 02-02-2010 05:35 PM

Quote:

Originally Posted by Marty S. (Post 393580)
Had the same thing happen on a 2 year old goodman unit last summer.

Were the pressures while operating close to normal though.

Marty S. 02-02-2010 07:06 PM

Good point, they were not . Head pressure was close but suction was way too high.

beenthere 02-02-2010 10:30 PM

Quote:

Originally Posted by Marty S. (Post 393637)
Good point, they were not . Head pressure was close but suction was way too high.

Thats why I think he just has a tech that doesn't know how to check out a heat pump in the heating mode.


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