View Full Version : AC Compressor question

Rusty Hughes, Indy
06-05-2003, 11:53 AM
Hello from someone who knows nothing about ACs,

Just had a visit from my heating and cooling specialist for my annual AC checkup. There are some numbers on the invoice that I don't understand and was wondering if anyone could explain what this means about the condition of my AC (year 1982).

Compressor Amps 10.5 (max 10.2)
Outdoor Fan Motor 1.2 (1.9)

It is a very cool day here so the AC has not been running at all. So shouldn't my compressor amps be below the max? Does this mean that I am using more electricity to run the AC than I should? If I am above max now, what will it be like when it is 90 degrees for the whole day?

And lastly, does it seem reasonable that buying a whole new AC unit would be cheaper in the long run than replacing the compressor?


Lee Schierer
06-05-2003, 1:03 PM
It depends on what the readings really mean. Where did the "MAX" numbers come from??? When whas his Ampmeter calibrated? What was the line voltage when he took the readings. Power = Amps X Volts. Given cold temps, I would expect a compressor on an A/C to run a bit harder than when it is warm. There is oil and grease inside. I'd let it run 20 minutes or so and see what the reading is.

Is the guy just trying to sell you a new unit because his business is slow? It doesn't sound broken to me, but I'm not an A/C expert either. Not sure I would lose any sleep over a few tenths of an amp.

Try oiling the bearings on the fan motor. They take lots of abuse from the weather. I would think replacing the fan motor would be no big deal. Replacing the compressor will be mucho bucks.


Ken Garlock
06-05-2003, 3:44 PM
Hi Rusty.

I don't understand what the 10 amp number represents. Is it the steady state current draw when the compressor is running, or is it what the technician thinks is excessive current over and above the steady state current?

A 10 amp current draw is not much for an AC system. At 10 amps, you might be able to assume a 2 hp motor(at 230V.) A rule of thumb is that it takes 1 hp to provide one ton of cooling. One ton of cooling is around 12,000 BTUs. With that in mind, we can fudge ourselves into your having a 24,000 BTU system. BTW, the term "ton" rating of compressors comes from the fact that one ton of ice gives a certain amount of cooling as it melts. If an AC unit gives the same amount of cooling, it is a 1 ton unit.

Setting aside all the above, there are really on two things you need to worry about with your AC. 1) Does the technician say that the pressures at the compressor connection are correct? There are two to be concerned with, the high pressure gong to the evaporator where the air is cooled, and the "suction" return line. 2) What is the temperature at the duct outlets in the rooms. Another rule of thumb is that the air coming into the room should be 20 deg. cooler that the ambient room temp.

One last comment, you should never have to add refrigerant to an AC system. It doesn't wear out, and the only place for it to go is out through a leak. IF you have to add, you need to have the leak addressed.

Your system is 20 years old, but I wouldn't worry until it give out. Heck, it doesn't get hot in Indy. :) I would be more worried about the heating system part of the HVAC package. Heat exchanger tend to rust out and can subject you to dangerous fumes. If it were me, I would run with it this summer, then about September look for some deals in new brand name systems.

My limited knowledge comes from dealing with HVAC people over the years, and what I learned from my Dad who was an HVAC maintenance foreman at BF Goodrich for 40 years.

Jason Roehl
06-05-2003, 7:32 PM
Based on the cool, but not cold weather we've been having for the past 2 months, Rusty, I would say that dude is trying to sell you a new system!! No heat OR A/C biz right now.

Paul Geer
06-06-2003, 9:32 AM
Hi Rusty,

(1) I would say replace the the outdoor unit, after 20 some years, the condenser is losing the compacity the transfer heat from the refrigerant to the air, there are copper tubes running though the aluminum cooling fins and the bond between the copper and the aluminum is starting to fail and putting a added load on the compressor.

(2) If the condenser fan motor bearings are starting to drag, slowing the fan down (adding more currant draw by the fan motor) , that would also put more heat load on the compresser, You could oil it but then that would temperary solution. The bearings are damaged already. You could replace the fan motor but again there's that condenser.

So I don't think it would unreasonable to replace the whole cooling system, even though you could you get away with replacing the condenser only.

And of course have the furnace checked as well. I'm sorta in the same boat, just bough a house and it has a Lennox Pulse (1985) with an Lennox AC, maybe the same year, so far so good :) nkock on wood.

I spent 12 years putting the things in, and now 15 + years servicing them, including doing the woodworking here at IU.

Here's one other little thing to check, dirt and dust in the condnser, either blow it out with compressed air or wash it out with a garden hose, shut off the power first and watch the water around the motor.

Carl Eyman
06-13-2003, 1:57 PM
My condo was purchased new in 1982. In the fall of 2001 I had the whole heating/cooling equipment replaced except for the ducts, of course. I am saving about $50 per month on my electric bill June thru Sept. - something less in the cooler months, of course. The unit is quieter as well as more efficient. You ask why change it when not broken? Well I think I was the only owner out of 23 total units that had not had to replace a unit because of breakdown. I got a little better price in the fall. I feel better when I see my electric bill anyway.

David LaRue
06-13-2003, 2:28 PM
Having gone though A/C and Heating problems in the past (thank goodness for a couple of CO alarms in the house when the exchanger went) If you do decide to replace consider this:

You probably want to think of replacing the A/C and heating system as a unit. Most likely you will need to size the A/C for the new heater. They are are now much smaller in size than the old ones and much more efficient. Plus you will get a better deal, and one hopefully sized right for your house. Note that natural gas has increased 100% over that past year and Greenspan doesn't see a short term solution. So, if your electric is from a natural gas fueled plant, and your heat is natural gas, the your return on investment, ROI will be shorter than in the past. Plus factor in the SEER ratings of 12 plus, and payback, depending on how much you use it will be reasonable. Since it is slow, you may have more leverage to negotiate with other HVAC vendors now, rather than wait for this winter when everyone will want to replace their old units, because of their high gas bill. Plus it is better to do it now than to decide to replace the furnace when its 15 degrees outside. (That's when mine failed :( ) If I was to do it over I would consider one of the units that has the fans running on low all the time to circulate and filter the air in the house.

Best of luck, never an easy decision.


Jim Becker
06-13-2003, 3:43 PM
Originally posted by David LaRue
You probably want to think of replacing the A/C and heating system as a unit.

I agree totally and just did exactly that...with a 92% efficent two-stage gas furnace (about 2/3 the previous inefficient unit's BTU rating) as well as a 13 seer two-stage A/C unit. Gas usage the first month was 15% less than the previous year in the same period and we expect some noticable savings on the A/C side, too. Our old furnace was still kicking, but the A/C was shot. We feel it was a good investment and now have a system that is more even throughout our home, whether heating or cooling, and with significantly better filtration.