Air Conditioning - A/C will not cool

My AC unit just will not cool the house down. Everything is running, there is plenty of freon and the compressor seems to be good. All filters are clean and fan is blowing, the only thing I can see is the suction or low side of the compressor pressure is swinging 12 to 15 psi. I don't know what that means, if anything. Can some one please help with a suggestion. Thanks.

Is this a new install or your first time using it (recent house purchase)? I guess what I'm getting at is:

1. Has it worked before?

2. If so, has anything significant changed such as additional square footage added to home (even changing to vaulted ceilings adds square footage), etc?

15 psi on the suction side is the problem. Either you are out of freon or the system is restricted.
I suspect you may not be certified to handle refrigerants.

Low side means very little without the high side reading/outside ambient plus interior return temp. I would first investigate the cleanliness of the coils especially the evaporator. If your evaporator coil is partially frozen (big ole chunk of ice) you could have a unusually low reading such as this even with a full charge level. You see a lot of units get overcharged with refrigerant due to careless techs not letting the unit throughly thaw before recharging. But as noted you need to be sure and have the proper EPA refrigerant handling certificate before fooling with the internal sealed system. And also there could be a restriction etc etc. If you have the EPA thing and some training as to how to safely do high pressure system checks I guess can DIY but please be careful Safety glasses and gloves are a must anytime dealing with refrigerants. You are probably well aware of the risks (especially eye injury or blindness) if you have some training, just thought I would bring that up.

Thanks to all of you for your help; no I am not a tech, but my uncle is and he looked at it and added some freon. After reading alot of these messages I checked the system again. From what I've learned the High side line should be warm to hot almost too hot to touch and the Low side should be cold and wet but not frozen. The low side is cold and wet, not frozen, but the high side is room temp. not even a little warm. What do you think may be the problem. Hopefully not a bad compressor. Please let me know.

Thanks to all of you for your help; no I am not a tech, but my uncle is and he looked at it and added some freon. After reading alot of these messages I checked the system again. From what I've learned the High side line should be warm to hot almost too hot to touch and the Low side should be cold and wet but not frozen. The low side is cold and wet, not frozen, but the high side is room temp. not even a little warm. What do you think may be the problem. Hopefully not a bad compressor. Please let me know. Also all of the coils and fins and filters have been checked and are clean. I do however have an air flow issue. I have a 4 ton unit which requires some where around 1800 cfm I think and according to my duct chart my current return ducts are only cabable of moving about 1200 cfm. So we are going to put a larger return line to make up for the differecne. Again I am not a tech and I do appreciate the safety tips and I will not be attempting any of this with out a tech present.

Sorry. I meant to answer your questions. No it is not a new house, I have been in it for 6 years and the system was put in when the house was built 3 years prior to that. Yes the system has worked before, it was working fine until about 4 days ago. And No there hasn't been any changes in square footage or to the system itself.

The small line will not always be warm to hot. Sometimes just a little above the outdoor temperature. Cold & wet on the large line is good. Before calling your uncle back, take a thermometer & put in the return duct close to the air handler. Wait about 5 minutes & take a reading. Repeat on the supply side. There should be 15-20 degees difference. With the undersized duct, the difference is likely to be 20+. Let us know.

I did try something close to what you are suggesting but I used a laser heat gun. I shot the return register at the filter and shot several of the supply registers around the house and the delta T was only about 5 to 7 degrees. I will try your suggestion with a themometor unless you think what I did was enough for you to guide me to the next step. Again, thank you for all of your help.

When you say the pressure is swinging do you mean that the pressure rises 15psi then drops 15psi continuously ??

You need to use a stick type thermometer to check the air temp. The infra red is reading surface temp, not air temp.

Yes, the low side pressure will be within 5 psi of the high side for a few minutes and then will drop about 15 psi for a minute or two then slowly come back up to within 5 psi of the high side. The high side remains constant the entire time. You are write about the infra temp it does have to read from a surface so I will use a thermometer to check this next time.

With the low & high side pressures being that close together, it is almost certain the compressor is bad. Time to make the call.

That is what I was afraid of. My uncle is comming back out tomorrow to take another look, but I'm thinking you are right we will probably be putting a new outside unit in. Thank you so much for your help, everyone. This is the first time I have used a web site such as this and I have learned ALOT.

Thanks; Timmy