A/C unit help

For the last couple of months every once in a while my wife or I would come home from work and its hot inside our house. We normally keep the thermostat on 75 degrees. So I will turn the unit off at the thrermostat and let it defrost for atleast an hour and then turn it back on. Most of the time it will start blowing cool air. Sometimes I have to turn it back off b/c you can see the frost build up again on the line from the ac unit to up under the house. It is a split system. So I had a guy come look at it yday and I told him that it hasn't froze up for the last week. He put his gauges on it and then crawled under the house. He came back and said the (whatever is under the house) lines are sweating on the duct work and it has rusted a leak. So its cooling under the house and in the house. He put about 2 pounds of freon in it and I asked him what he suggested and he said its up to us. We could see how it goes or put in a new unit. He said if we did a new unit, he would recommend putting in new duct work throughout under the house b/c the new unit is going to sweat more which will rust out even more. He said for a 3 ton unit and new duct work it will be roughly $5,000. What would ya'll do? I told him I would have to go get a loan from the back b/c I didn't think that much.

 

he sounds like a ding dong I would call somebody else

 

How old is your house? My pops house is a 70s or so. Ac unit never gave us a problem. I don't think you'd need a new one. These new units don't last as long, at all.

Is that freezing the problem, or what's the problem?

 

Our house was built in 1983 or 84. When I told him that is wasn't freezing up all the time just every once in a while he didn't know what the problem could be. We had more trouble with it in June when it was really hot. Then I just set the temperature on the thremostat to cut off and let it stay off for a couple of hours and then it would come on and work fine. Just didn't want it to run and run while we were at work. So I'm not really sure what to do. I'm probably going to try to go under the house and look for the rusted out spot and can you repair that with some sheet metal and some duck tape or something? Also, I don't think this is the original unit b/c there is another air handler under the house that is not being used.

 

First thing is crawl under the house and look for yourself take pictures and post them.

 

Yeah I think I''m gonna do that this afternoon when I get off work.

 

X2

I would apply duct seal to all the duct connections in the crawlspace... and maybe wrap it in insulation.

Your evaporator is freezing up because either your filter is too dirty and not letting air pass over the coils.... or the refrigerant is way low.

Have a reputable HVAC tech use a sniffer to find the leak and braze it.. and if he does any brazing without running nitrogen through the lineset, kick that guy out of your house and find another tech that will braze with nitrogen.

 

One more thing, When was the last time the condenser coils were cleaned?

 

Sorry for my ignorance, but where is the condenser coils? Is that the coils on the unit outside? I cleaned them last year but the unit is under two trees and there's not much grass in that area so I'm sure it is dirty. The guy did tell me to get some coil cleaner from lowes and spray it out.

 

You got it right. The condenser coils are outside and the evaporator coils are in the air handler (the unit in your house).

The condenser coils outside actually contain the heat that was in the house... the fan pulls air through those 'hot' coils to get rid of the heat.

If you have dirty coils, the heat cannot be effectively removed from them. Bent fins (many of them) can be a problem too, comb them straight if possible.

 

Sorry for so many questions but how do you comb the fins back straight if they are bent? Will the spray cleaner in a can at Lowes do a pretty good job of cleaning them? I've read on the reviews that it may take more than one can

 

...can you access the evaporator coil (that's the one on the furnace unit inside the home)?.. if the evaporator coil is freezing up, then the issue is an inability to transfer heat to the refrigerant; ...filter problem, coil problem, ...

 

There is a little tool that looks like a comb. It is made of plastic. You use this to gently straigten any bent fins. This fins are very light aluminum and can be straightened very easy, but you must not damage the supporting tubes the fins are attached to. Damage the tubes and the refrigerant will be reliesed.

Harbor freight has them. they are cheap.

 

Sounds like a dirty evaporator, since it probably an A coil in the plenum, it is likely clogged with dust bunnies ( scientific term) . File ifr is right a fin comb will help or you may need to use something like blast a coil, or calgon cal clean. Good luck, and post your results.

 

What are the Low side and High side Pressures? and I take it that the system is using R22?

Pressure in the air conditioner's refrigerant suction line (low side pressure during compressor operation) and this will be a relatively low number, often less than 100 psi but not below 68 PSI.

(high side pressure during operation) is the pressure of the compressed refrigerant gas as it leaves the compressor motor. In other words, refrigerant gas returns to the compressor through the suction line from the cooling coil (which is cooling inside air) and should be somewhere in the 225-255 PSI range now this is all depending on 90-98 degree day.

 

I did know the low side and high side pressures that were on the gauges but I forgot now. I want to the low side was around 80 and the high was 240 I believe. I'm not saying this was the issue b/c the maintenance guy here at work don't think so. I got some coil cleaner and sprayed on the outiside part of the unit and used a water hose to wash it out and it hasn't froze up since. We haven't had any or many 90-95 day temps lately either though.

 

Buy some insulation to put on the big freon line, home depot might have it. Its specific for freon lines. Re wrap the pipes. Then seal up the wholes in the duct with sheet metal if they are big. Use the silver metal tape, not duct tape to seal up the ducts after that and maybe even mastic (duct sealer). Should solve the sweating and possibly dust problems.
If the duct with a hole blows out cold air it should have insulation on it too. Indoor coil may need to be cleaned but is a little more complicated.

They make cans of sealer to go inside the system but Im not sure how good the stuff works. The coil could just be rusty and leaking if it is old. Or the lines could be leaking.

If you clean the coil and re wrap the lines your unit might start working more efficiently and could start freezing up again.

Also you can SHUT THE POWER OFF TO THE OUTDOOR UNIT! Then take the top off and was out the crap from the inside too. Might help some.

 

Also the pressures can vary depending on outdoor temps and stuff.

 

Ok guys, here's a little update but still nobody knows what is going on. Another HVAC guy came out (repitable too) and he said it was only 1/2lb low on freon and then he cleaned the coils on the outside unit. A couple days later I called him back and said I was freezing up again. He said "you're kidding", so he came back out and went under the house and check the coils under the house since its a split system and he said they were clean. On the thermostat inside the house, He said for me to leave the system to ON (of course) and the Fan in the ON position over the weekend. So when the thermostat is "satisfied" the fan under the house still blows air. So I did and we haven't had anymore problems. He told me to call him after the weekend, so I did and he didn't answer. I left him a voicemail saying we didn't have any trouble but I haven't heard back. We got the light bill today and we got to figure this thing out. $100 more than last month. I called him again today and it rang a few times but went to voicemail again. Do any of you know what is wrong with it? Could it be something to do with the defrost switch or whatever? He did say that the unit was in good shape for the age, he said if the numbers are right on the serial number then its a 2003 model.

 

Can you give me the M# and S# or can you post a pic of the data plate I will look up some stuff here at work as I have some manufacture direct website info since I am a Chief Building Engineer here in DC.....

There is just a lot of stuff I need to know like Full load amps,Run Amps,compressor tonnage etc:

How far is the Condenser from the air handler?

What are the coil temps on the gauge set?

What is sub cooling and super heat?

If the fan running at right RPM's on both units?