Central AC still not working well, please help!?

Question

This is the continuing saga of our Central AC: We replaced the outside unit last November. It is a 31/2 ton, and that is the same size as we had. This year, the coil went out. Replaced the coil, not cooling enough, replaced the coil, and again..... We are on the 4th coil, 2nd AC guy. Both contractors said that the coils they installed were fine, they say the problem is in the ducts- they are 30 years old, and worn out. So..... I personally replaced the ducts. Checked for leaks. Temp at coil is 68, temp at outlet (register or damper, depending on who we've talked to) is 70. Temp in house is 83. It all worked great last year, any idea of why it is not working this year?????? ANY help/ideas would be greatly appreciated!!! Thanks.

Answer 1

Check the temp of the air going into, and leaving the furnace / ac system,  you should get a minimum of a 20 degree drop across the inside coil, or something's amiss.  Take a measurement where the filter goes in, then another at the first air outlet point you can find.  If you're not getting the 20 degree drop, the system's not doing what it should, mechanically.  If the problem with the ducts is that they're undersized, you should actually get more of a temp drop, but end up with a system that will not move enough air throughout the house, and will likely cause the compressor to fail before it's time.   What you really need is a GOOD hvac tech to look the situation over, and give you an honest answer to what's going on.   You may be ready for hvac tech #3.  Ask around, maybe someone you know knows a tech they trust.

Best of luck.

20+ yrs hvac tech.

Answer 2

it also could be since you last used your ac last year the filter NEEDS to be CLEANED

good luck

Answer 3

check your heat strips

Answer 4

Did anyone try to recharge the freon in this unit or check for freon leaks?because it does not sound to me like it has any.Good luck

Answer 5

Your temp at the coil is too high. Should be 10 degrees cooler. The proper way to check temperature is inlet (at the filter) versus outlet (air off coil). This should be 16 to 20 degrees differential. Less would indicate inefficient cooling (from your outside unit -possibly dirty coil) or too much air flow across your evaporator. If higher (22 or above) indicates too low air flow or dirty evaporator coil.

Rule of thumb: the lower the refrigerant temperature the less heat per pound it can carry.

Some high efficiency units that are not matched properly or not maintained properly will not cool the house sensation wise, compared to the older units.

Answer 6

My guess is that it might be the fan speed. If it doesn't force air through the ducts fast enough, it won't do a really good job cooling the entire house. You could adjust the speed by popping  the front cover off your furnace, you should find a jumper labeled "high" and "low". Try moving the connector to the high setting and see what happens. Good luck.