AC works. Blower inside runs. Fins clean. Filter new. Outside fan runs. Compressor runs. Cooling fins clean. AC repairman checked pressure and said it was fine. But I'm roasting. I only get 5 degrees of cooling measured between the intake vents and register air.
Help. What am I missing? The unit is 20 years old and maybe it's bored with work but I just cant afford to replace it.

 

Go outside and feel the two copper lines connecting to the outside unit. The larger diameter line (should be insulated) should be nice and cold, while the smaller diameter line should be slightly warm. If the large line isn't cold, or just cool, the system isn't working properly. Either the system is low on refrigerant (I know that tech said it was okay) or there's an obstruction (e.g. bad TXV). Are you getting a "normal" amount of air coming out of the vents? Often, if the system is low on refrigerant, the evaporator coil will freeze up, significantly reducing the airflow.

 

The large line isn't cold. Its 90 degrees and the small is 88 degrees.

 

What about the airflow, does it seem like a "normal" amount?

 

Welcome to the forums.

90° on the suction line won't yield much cooling.
I don't see how the refrigerant pressures could be normal. I can't discuss them on this board but it might be time to call that tech back .

 

Or call someone else. Once or twice I've had a repairman come out for something or other, and their answer was "it's normal" or "can't find anything", when indeed there was something wrong. I got the impression they were just lazy and didn't really feel like doing the work. Or perhaps, he didn't feel the work was worth doing, you know? Yeah, I'd get someone else.

 

Is has some serious problems.
Do some easy safe temp testing on your own to see if it's way under-performing:

This is a check to see how your system is performing in respect to its 'Nominal Rated Btuh' you need at least the following numbers:
Performance Data Collection – Best Time to collect data is Late afternoon around 4:30 pm, when attic is HOT; also when outdoor temps are around 85; 95; 100°F etc.

*All you need is a good air-probe thermometer (digital reading in tenths preferable) & and indoor Humidity Gauge Walmart has a good digital humidity gauge... everyone needs one! Around $8.00

That data form is only a partial check so a contractor can be called, & should NEVER-EVER be used to try to fix something, only technician's have the high priced necessary test instruments to check superheat & sub cooling & the MFD of capacitors, and so on; you are apt to cause a lot of serious damage to the system because everything has to be done just RIGHT...!

1) Helpful; Tonnage & SEER ___________ of Unit & outdoor
condenser model number: __________________
2) TXV or, orifice metering device? _______. Only if U know…
3) Outdoor condenser’s discharge-air-temperature ______°F Subtract
Outdoor air temperature: _______ - from cond. air _______ =
Condenser Air-Temp-Split ______°F
4) Need the ‘Indoor’ percent of relative humidity - away from Supply-Air outlets ______

5) Indoor Return-Air Temperature ______ °F Subtract Indoor Supply-Air Temperature ____ °F Indoor temperature-split _____°F

Fill-in the above information for troubleshooting & performance analysis.
A high indoor split with low outdoor condenser split = LOW indoor airflow (common problems) or dirty blower wheel & evaporator coil.
Low indoor split very-high outdoor split = drawing Hot Humid air from the attic or outside source into return-air duct to evap-coil.

At 50% indoor RH the indoor temp-drop should be around 18 to 20°F. Outdoor condenser split varies some according to the SEER of the condenser; higher SEER lower split. It is important to check it...!

These simple skills will help to protect the compressor from early costly failure & protect you from many huge & needless future high dollar costs!
If you're lacking in knowledge you cannot protect yourself from a poor performing HVAC system or incompetent service...

 

I appreciate the advice. The tech came out originally because the compressor wasnt running. Replaced the capacitor. System started putting out moderately cold air. I watched him connect his guages and saw it was in the "green" zone. But perhaps all the activity with an old unit has caused a leak and now thats the problem. I'm going to borrow a friend with a guage and test again.
If the system is sealed...why is there a line dryer? How could that be useful? If it is doesn't that mean the r-22 can get less pure over time? Also, can the copper tubing get clogged? I can't imagine how but logic is failing me.

 

The liquid-line filter-drier is a good thing & helps keep the refrigerant clean & dry; check temp-drop across the drier to reveal a restriction.

The service Tech's job is to always find & fix any leaks & then check indoor airflow so that it is delivering the correct CFM for your climate conditions. After that charging the system using superheat with a fixed-piston-orifice or subcooling with a TXV metering device.

You use both SH & SC along with pressures to troubleshoot the system...

 

When sources talk about replacing the line dryer they dont say: Connect equipment to contain the r-22 and later restore it. They just talk about copper braising or welding or soldering. Are they assuming thats a given? Can you do any of this work without needing to reclaim and/or replace the refrigerant?

 

The EPA has mandated that only a licensed tech can handle refrigerants like that and they cannot be deliberately released into the atmosphere..... they must be reclaimed.

 

Right. My question is: Does replacing the line dryer release r-22?

 

The filter-drier is in the refrigerant line. You have to "open" the system and reclaim the refrigerant in order to replace it.

 

Thank you. I'm absolutely going to understand all this if it takes me 3 years and 5000 questions.

 

Is every part of the system sealed together? Or put another way, can you replace any component beyond the capacitor and obviously seperate wiring/electrical components without reclamation equipment? Legally.

 

In a word, no. Apart from the electrical components (contactor and capacitors and possible time delay circuit), just about everything else has refrigerant passing through it (compressor, condenser, evaporator, pressure switches, lines, etc.).

 

You can valve-off the liquid service valve & have the compressor pump the refrigerant into the condenser. However, it is possible to damage a Scroll compressor if it goes into a vacuum; so it is better to recover some of the refrigerant.

You have to take refrigerant somewhere to get it reclaimed so that it can be reused.

 

This diagram is a generic one that illustrates the piping interconnections.