AC Problems

[Byron Trantham]

My central air is 14 years old and still working or at least I think so. I had the compressor charged this Spring but it just can't cool the house down "like it used to." I have had two different companies out to look at it. It seems they want to replace the condenser ("A" frame). They say that cleaning it (the cooling fins) would cost as much as replacing it. I used compressed air and put my hand behind the air stream and determined that air was passing easily through the fins BUT it did blow out a bit of dirt. The result seemed to improve the performance but I knew I needed a hot day to figure out if could keep up. Yesterday was the day and it didn't. IT got to 73 degrees and stayed there all day. (The set point was 71 degrees.) It was pulling humidity out of the air as the condensation pump was pumping water into our deep sink. My next step is to use Simple Green sprayed into the fins and then back wash with clean water. I intend to do this tomorrow morning and tomorrow is supposed to be hot again. Anyone know if I am "fighting the tide?"

It just seems that spending $1200+ for a "maybe fix" is a bit pricey. Any opinion will be greatly appreciated. Frustrated! :(

[Ken Garlock]

Hi Byron. I think you have your terms mixed up. What I know as the "A frame" is the upside-down "V" Evaporator in the plenum of the furnace. The condenser is the coils surrounding the compressor outside. You are smart to clean the evaporator coils, they can get pretty dirty. But, also clean the condenser coils outside. They are just as important as the evaporator coils. Usually a garden hose is all that is needed.

Basically, there are only three things that can go wrong in an AC unit. 1) a leak in the tubing thus releasing freon. 2) a bad expansion valve, (aka capillary tube,) in the evaporator. and 3) the compressor wears out. A good AC man can zero in on the problem quickly.

With a 14 year old unit, you are into the declining years of your system. A new AC system is not out of the question. While you are at it, check the conditon of the furnace. The heat exchanger in the furnace can/will rust through and expose your family to CO fumes.

Finally, $1200 for fixing an evaporator sounds very high to me. For $1200 you should be looking at a complete low-end AC system, IMO.

[Byron Trantham]

Hi Byron. I think you have your terms mixed up. What I know as the "A frame" is the upside-down "V" Evaporator in the plenum of the furnace. The condenser is the coils surrounding the compressor outside. You are smart to clean the evaporator coils, they can get pretty dirty. But, also clean the condenser coils outside. They are just as important as the evaporator coils. Usually a garden hose is all that is needed.

Basically, there are only three things that can go wrong in an AC unit. 1) a leak in the tubing thus releasing freon. 2) a bad expansion valve, (aka capillary tube,) in the evaporator. and 3) the compressor wears out. A good AC man can zero in on the problem quickly.

With a 14 year old unit, you are into the declining years of your system. A new AC system is not out of the question. While you are at it, check the condition of the furnace. The heat exchanger in the furnace can/will rust through and expose your family to CO fumes.

Finally, $1200 for fixing an evaporator sounds very high to me. For $1200 you should be looking at a complete low-end AC system, IMO.


Ken,
Great response. First, you're right about my use of the terms, sorry about that. Second, the AC guy did clean the outside condenser coils - very well. Finally, I now have a working knowledge of the basic components of the system. One of the techs checked the current flow at three or four locations in the compressor and determined that everything is nominal. BTW, I have a 4 ton unit for the mail level of the house and a 2 1/2 ton unit for the upper level. It's the 4 ton unit giving me fits. An evaporator for a 1 ton unit, installed was quoted at $900 then they found out I have a 4 ton unit and it costs about $1,200 installed. They quoted a Trane 4 ton compressor for about $4,000.

I'll let you know if cleaning the evporator helped. :rolleyes:

[Tyler Howell]

Thanks Ken for the schooling.
Just a note to all. What ever you spray into your system for cleaning, You will be breathing for a while. One of my towers was evacuated because of a over zealous maint. man.:eek:

[Randy Moore]

Byron, did the AC Tech check the freon in the system? Check your return air and supply ducts grilles for anything that might be blocking them. Make sure the connections in the breaker box are tight as that can cause problems too. Have the thermostat checked, it could be off.

Also you said it got to 73 degrees and the set point was 71 degrees. I would say that everything is OK. T-Stat might be out of whack

[Bill Turpin]

The only reason an evaporator coil needs to be replaced is erosion of it's aluminum fins. Less surface area means that less cooling work is done. If the fins seem to be all there, are not pitted, etc, this is not your problem. All of these prices seem HIGH. EPA regulations require service people to reclaim the old freon. This has added hours of labor and disposal costs to all of this. I would suspect, with the age of your system, that worn discharge valves in the head of the compressor. The compressor is pumping but some of the freon is leaking back into the cylinder. This can be difficult to detect in a residential system and amp draw will not reduce that much. If you truly have an expansion valve, it might not be feeding enough freon. Determining what is going on inside a closed system is somewhat "smoke and mirrors". Having spent 35 years in this industry, in four states, and on both sides of the parts counter, I would say that at least 80 to 90% of the servicemen are NOT TRAINED PROPERLY.

About 90% of all defective AC compressors fail beacuse of DIRTY filters. Poor air flow causes liquid slugging of freon, which damages valves. Bad valves cause overheating of comp. which leads to motor failure. Then everybody wants their insurance company to pay for lightning damage. Not, this was caused by failure to spend a dollar six months to a year earilier for a filter. Do not buy a filter that you can read a book through. If you can see thru it, dust will pass also. If this system sees the sawdust from your shop, you need to check the filter fairly often (less than monthly).

The most important thing you need to do is find a knowledgeable and HONEST service company. I appoligize(spelling?) for the rant.

Bill in WNC mountains
NC refrigeration license #2821

[Ken Garlock]

It is good to see a professional response. My knowledge of the AC area is from my father who was head of the HVAC repairmen at BF Goodrich back in Ohio. Like many things, the principals are straight forward, but knowing the details is where it counts. You know the details :)

[Jim Becker]

When you combine the age of your system with the vast improvements in efficiency of current systems, it's certainly worth investigating a complete replacement. We did that last year and went from an "old honker" to a 92% efficient gas heat/13 seer AC system. Although the rise in fuel cost has increased the payback period, the long warranty and much more even comfort we are enjoying was worth it. Some utilities also have rebate programs which get you anywhere from $200-500 back towards the cost of the system and 6 month/no interest financing also helps.