Central A/C acting up...what gives?

ELI(NJ) · 07-10-2009, 01:12 AM

Hi all, and thanks in advance for the help.
I moved into my current house 3 yrs ago, and the AC was just adequate on very hot days (say 85 deg). Last year it was less capable, and this year it is even less so. I've had it checked and charged (more or less R22 didn't really change much). It is a 10 yr old Trane XE1200, 2 ton unit, details below:

On a sunny 75 deg day, moderate humidity, it had the following condition:

Low side pressure = 90 (line a bit cold and sweaty to the touch)
High side pressure = 150 (line barely warmer than ambient temp)
Pressure when compressor goes off equalizes in 45 sec to 1 min
Compressor/condenser never too noisy or hot
Air duct inlet temp = 76
Air duct outlet temp = 65

Before I pay someone thousands to take a stab at maybe fixing it, does it seem like compressor/condenser, evaporator/orifice, or refrigerant line issue (too much oil or dirt)? I've been told different things.

yuri · 07-10-2009, 05:54 PM

Your compressor and its valves are worn out. Should have pressures like 225/65 which gives you a 3:1 or 4:1 compression ratio. 150/90 is less than 2:1 and it is not pumping enough/worn out. Time for a new unit. Compressors are very expensive to replace and the r22 is going obsolete next year.

hvaclover · 07-10-2009, 06:03 PM

We got a simple one on a Friday evening? Crap, there goes my site OT pay

.

HvacWiz · 07-10-2009, 06:35 PM

Quote:

Originally Posted by yuri

Your compressor and its valves are worn out. Should have pressures like 225/65 which gives you a 3:1 or 4:1 compression ratio. 150/90 is less than 2:1 and it is not pumping enough/worn out. Time for a new unit. Compressors are very expensive to replace and the r22 is going obsolete next year.

R-22 is not going to be obsolete next year, only new units will not be made that contain r-22, R-22 will be phased out by 2020.

hvaclover · 07-10-2009, 06:43 PM

Quote:

Originally Posted by yuri

Your compressor and its valves are worn out. Should have pressures like 225/65 which gives you a 3:1 or 4:1 compression ratio. 150/90 is less than 2:1 and it is not pumping enough/worn out. Time for a new unit. Compressors are very expensive to replace and the r22 is going obsolete next year.

They stop making r22 next year (as long as the powers that be don't have a last minute change of policy).

Still be recycled 22 around.

yuri · 07-10-2009, 06:49 PM

For about $100/lb.

You get OT. Geez I would accept a decent piece work rate, say $10/post.

hvaclover · 07-10-2009, 07:25 PM

Quote:

Originally Posted by yuri

For about $100/lb.

You get OT. Geez I would accept a decent piece work rate, say $10/post.

I'll talk to the Boss for 'ya.

ELI(NJ) · 07-10-2009, 10:58 PM

Thanks Yuri, I was leaning that way but didn't want to face reality I guess. I knew the pressure difference was very low, couldn't an oversized or worn orifice do this? Just out of curiosity, does the 45 sec equalization raise concern too? Also, you say replacing the compressor only isn't worth it, even if the coil and the rest are perfect?

Thanks again guys...

hvaclover · 07-10-2009, 11:02 PM

Quote:

Originally Posted by ELI(NJ)

Thanks Yuri, I was leaning that way but didn't want to face reality I guess. I knew the pressure difference was very low, couldn't an oversized or worn orifice do this? Just out of curiosity, does the 45 sec equalization raise concern too? Also, you say replacing the compressor only isn't worth it, even if the coil and the rest are perfect?

Thanks again guys...

Yep.

Time for a new one.

newtech · 07-11-2009, 06:54 AM

Quote:

Originally Posted by ELI(NJ)

Thanks Yuri, I was leaning that way but didn't want to face reality I guess. I knew the pressure difference was very low, couldn't an oversized or worn orifice do this? Just out of curiosity, does the 45 sec equalization raise concern too? Also, you say replacing the compressor only isn't worth it, even if the coil and the rest are perfect?

Thanks again guys...

How old is the condensing unit? You said it was in good condition, if so then I would say go ahead and change the compressor. But, before you do I would have a qualified tech check out the rest of the system first to make sure everything looks good. Something took out the valves on the compressor. Need to find out what caused it before you put in a new compressor, or the new one will be sitting next to the old one in the scrap yard.

yuri · 07-11-2009, 09:11 AM

The 45 sec eq rate is a bit fast and the bad valves indicate that. I have never heard of a worn piston or orifice and it is probably impossible. Would have to have grit flowing with the freon and it would plug the strainer first. If it was oversized then it would not have worked good from day one. May cost up to $2000 to replace the compressor (local market prices may be higher/lower). If the A coil springs a leak or other expensive problem occurs you may regret it. Where do you live? If you spend a lot of the year using it or have high humidity then a more efficient/higher SEER unit may save you lots of $$. Check for rebates from the gov't/power co as they are available for higher SEER units.

ELI(NJ) · 07-11-2009, 11:36 AM

The condenser is 10 yrs old and appears to be in good shape overall. I may have found the Climatuff compressor for around $900 before install, would that make it worth it then?

I'm in NJ so the AC is used about 4 months a year to cool the upstairs, which has an attic exhaust fan too. BTW, the downstairs unit is the same size, and similar age and type of unit, and is always ice cold...

newtech · 07-11-2009, 11:47 AM

Quote:

Originally Posted by ELI(NJ)

The condenser is 10 yrs old and appears to be in good shape overall. I may have found the Climatuff compressor for around $900 before install, would that make it worth it then?

I'm in NJ so the AC is used about 4 months a year to cool the upstairs, which has an attic exhaust fan too. BTW, the downstairs unit is the same size, and similar age and type of unit, and is always ice cold...

$900 seem's like that should be close to the install price including the compressor. What is the model and serial number of the condensing unit?

yuri · 07-11-2009, 12:43 PM

The upstairs unit usually runs more as heat rises. Prices vary a lot depending on the labor rates/cost of living in your area. $700 for a 18,000 BTU from Lennox my cost. Then the dealer marks it up and adds labor, use of recovery machine etc. It is worth replacing if you don't mind the possibility of future repair costs, ie: condensor fan motor. Did you have the unit serviced regularly, condensor coil properly cleaned, evaporator coil cleaned/checked. Those spine coils are nasty to keep clean.

psilliman001 · 07-11-2009, 11:02 PM

Quote:

Originally Posted by yuri

The upstairs unit usually runs more as heat rises. Prices vary a lot depending on the labor rates/cost of living in your area. $700 for a 18,000 BTU from Lennox my cost. Then the dealer marks it up and adds labor, use of recovery machine etc. It is worth replacing if you don't mind the possibility of future repair costs, ie: condensor fan motor. Did you have the unit serviced regularly, condensor coil properly cleaned, evaporator coil cleaned/checked. Those spine coils are nasty to keep clean.

.......will only give u usually only a one year warr. not worth it for all that money. New units nowadays have up to a 10 year parts warr, go with new unit . what if the cond fan goes or the cond coil springs a leak . err on the side of caution

.........Jack