Outdoor AC Compressor Replacement - double check

[crybdr]

I'm ready to replace my outdoor AC unit (and indoor coil). It's 17 years old and is not keeping up with the temps - it works all day and can't keep up.

I had a service guy come out to check it. He added freon and couldn't get any temperature change to occur. Additionally, after the freon add (or maybe before) a curious temperature gradient around the exhaust fan was noticed. His explanation was something along the lines of the system feeding itself - valves, relief valves or something like that. Basically, some of my coolant is bypassing the path to the house and recirculating through the outdoor loop. Here's a diagram of what's going on....



I know this unit is way past it's life probably. Does this failure mode make sense?

Just curious if there are any AC folks out there that could offer an opinion.

[crybdr]

Additionally....

The amp draw on the compressor was low - not working hard.

And, the thermocouple on the freon line running back into the house held steady at about 60 degrees - before and after the freon add.

[LCHIEN]

i never heard of that failure before but if you got 17 yrs from that unit its done its job.
I suppose if he adds freon and the temp doesnt go down and the amps don't go up then there's probably a closed loop bypass leak in the compressor as he says makes some sort of sense. usually the air exhaust is quite warm from the fan on the compressor - rmoving heat from the freon. Cold idicates the freon is expandin where it shouldn't be. Again, leak.

Pay the man. Al gore says its just going to get hotter. Oh, maybe he was talking about his new girlfriend. (humor, not a political comment! Don't respond except to do a ROFL, LOL or something, please).

[crybdr]

Yeah, 17 years is a lot to expect from anything.

I was 90% sure it needed to be replaced. He's been paid for his diagnosis time and the freon - and he will be the one to get the replacement business (and recollect the freon).

I just wanted to make sure I'm not missing the 'oh yeah, you could change out the $5 valve and make it work as good as new' scenario. Which, I doubt to be a workable solution - considering this unit's age, but worth a try.

I haven't worked with this contractor before and am simply double/triple checking. Thanks for the input.

I'm sure I'll be sweating less after the replacement.......

[LCHIEN]

A/C compressors are usually sealed units and not servicable.

[gsmittle]

i never heard of that failure before but if you got 17 yrs from that unit its done its job.

Pay the man. Al gore says its just going to get hotter. Oh, maybe he was talking about his new girlfriend. (humor, not a political comment! Don't respond except to do a ROFL, LOL or something, please).

Now, if I could just get my 17-year-old to do HIS job…

Re Gore comment:

g.

[gjat]

I'm not an AC guy, but living in Florida, we learn a thang or two.
The freon works for heat exchange by pressure differential. When it goes from high pressure, to low, it loses energy and cools. When it compresses, it absorbs engery and warms. Or vis-a-versa. However, it is mandatory you have a pressure differential to create the heat exchange. That's what the compressor does. If the compressor isn't compressing, it's running without effort (low amps) and not creating a pressure differential to transfer heat.

[master53yoda]

If the condensing coil(out door unit) is u-shaped you will get a temp pattern off the fan somewhat similar to what you have drawn. as the air against the sheet-metal side doesn't have as much heat density as the other sides, because you say that some of the airstream is warmer that tells me the unit is working some. I would suspect either a plugged capillary tube or failed Thermal expansion Valve. on the indoor coil.

As for the description of the problem that the tech gave you it is a wild guess. If the unit has a Thermostatic expansion valve on the indoor coil and if that valve fails it will do exactly what you described as it makes the unit appear to be low on refrigerant with the exception of a liquid line temp that is close the the outside air temp instead of somewhat warmer, about 25 degrees. If the valve is bad it is simply not allowing the refrigerant into the indoor coil and the refrigerant just sits in the outdoor coil. which looks like not enough refrigerant.

Did the tech give you pressure readings and a superheat and sub-cooling reading. As well as supply air and return air wet-bulb and dry-bulb temps. if he did not get that minimum information he won't know what is wrong.

The high pressure bypass valve is inside the compressor and if it goes open you can hear it and it will overheat the compressor and shut it down on thermal overload in about 15 minutes, it will normally stay off for 2 to 3 hours then restart and do it again if that is what is wrong there isn't any guess work as the compressor is to hot to touch.

If the technician cannot give you a solid diagnosis with documentation to back it up I would not use him again . It sounds to me like he just wants to sell a knew unit. System life is 25 to 30 years if they are put in properly if not they normally die in about 5 to 7. 17 years is about like a 50 year old person. getting there but could live to be 100 if he gets the right maintenance.