It was kind of hard to look at the heat exchange fins due to the way the mechanism was mounted and the location of the access panel, but they seemed perfectly clean. Shiny metal and nothing left on my fingers when I touched it.
Sounds pretty clean. We can tentatively rule out low airflow across the evaporator, I think. The furnace fan *is* running, correct?
Just to be certain, the condenser is the big fan unit outside, right? That may well need to be cleaned. It's worth looking at, but I'm not going back outside in the heat today if I can help it.
Yep, that's it. Also, if the fan isn't running (burned out motor, bad switch, whatever) that would do it. The condenser fan should run with the compressor is running.
Like I said, the cold pipe was about as cold as the outside of a glass of iced tea. I would have hoped that it would be cold enough to be unable to hold onto it for very long, but I'm pretty sure that I could have held it indefinitely.
Was the evaporator quite wet? I want to know if the evaporator temperature is below the dew point.
As I understand it, the AC cycle goes like this:
- Compress refrigerant, which generates heat
- Dissipate as much heat as possible in compressor unit
- Pipe refrigerant to evaporator
- Allow refrigerant to expand, absorbing heat
- Pipe expanded refrigerant back to compressor
- Start over
Does that sound right?
That is *exactly* right. The evaporator and condenser coils are "heat exchangers", which attempt to change the temperature of what's inside them (the refrigerant) to the temperature of the ambient air blowing through them. That's why airflow through these coils is so critical.
My thought at this point is that it is not able to dissipate enough of the compressed refrigerant's heat at the compressor. Does that sound reasonable? (It could still be undercharged, but I'm going to save that as my last resort.) If so, the problem seems likely to be that the compressor isn't able to move enough air over the hot tube, which could be several things, but dirty coils seems likely. I'll check that when the sun goes down.
Yep, that's reasonable. Do you have an air compressor? If so, figure out which direction the fan is blowing the air, and then use your air compressor hose to blow the opposite direction through the coils and blow all the dirt and leaves and shit out of it. Really the only other thing it could be on the condenser side is the fan not coming on.
I expect you are low on refrigerant. Like the other Jim said, an AC repair guy is just going to put some more in and say "there you go" (because people seem inherently lazy). What you really want is a full evacuation. Ideally, you'd pump it down to a good vacuum and let it sit evacuated for a while, watching the pressure gauge (pump turned off). If it loses vacuum, which you can see on the gauge given some time, then you have a system leak. If you have a leak, then you have to find it. This is typically done by recharging with a refrigerant containing an ultra-violet reflecting dye. You charge with the dyed refrigerant, then run it for a while, then come back with your blacklight and look for where the refrigerant is leaking. Looking at your evaporator, there seems to be quite a bit of corrosion on it, so I would not be surprised if there was a pinhole leak where one of those tubes joins the heat exchanger area.
Jim
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