Yes, correct. Those are left and right from a Citation. Looking clean notwithstanding they're 27 years old. I'd like to get deeper down this rabbit hole chasing new ones.

Those pictures are perfect. They give the impression the units are fine without actually showing any detail of the fin condition. So you have no clue until you get one.

Mike C.

On this (timely) topic - can anyone recommend someone in the Texas region that actually understands A/Cs and will take the time to sort through mine? I’ve had my shop work on my Keith system in my 501 several times but it’s just not cutting it once it gets over 90F. Getting at best a 20d drop. Tons of airflow in the back, but very little airflow up front. They say they checked the ducts and didn’t find any issues. I have the cool sticks.

Thanks in advance,
Matt

20 degrees drop is the normal. I don't know what Nishant did to his to get his amazing results.

Jet Shades has been the lifesaver for me in the 501 cockpit. Everyone in the back enjoys cool temps while I used to cook up front (MU2 too). Jet Shades are a game changer. They block the heat tremendously. Worth every penny. Don't think that cheap tint shades are going to cut it, it's a greenhouse in the cockpit.
I also am super anal about passengers covering/blocking my only AC floor vent by the barrel seat. I bought the Cool Stiks system/STC but haven't been able to install it yet, but it will help with cockpit comfort too. Did I mention Jet Shades are awesome?

I let the airplane heat soak today for a few hours in the afternoon sun. Interior was 103. After turning on the A/C and letting it run for 10 minutes, the a/c was blowing 59F.

After running for 20 minutes, the interior temp dropped to 90. These systems are really under powered for the size of the cabin even when working optimally.

I invited Matt to come down so we could fix his a/c. 20 degree diff is not even worth having an a/c. A swamp cooler can do better than that.

Really high pressure on the high side due to an overly tight expansion valve setting and a somewhat slow blower speed on the evaporator.

The compressor will be working hard and you won't cool that well due to lack of good evaporator air flow.

It will also freak out passengers if the air is so cold i tis below dew point and the fog will look like smoke.

I had that once in my MU2 with the ACM.

Mike C.

None of those things are true in my situation. All speculation.

If you over charge the system, it reduces the cooling capacity. I absolutely did not do that.

There's a fine line in cooling speed where you don't want your system to cool too fast, but also not ever get the temperature down. If the system cools too fast you won't suck out any of the moisture and humidity will remain. Too slow and the ambient temp will over power it and moisture will collected on the cooling fins and freeze.

We deal with AC issues on our boat all the time and often feels like we are chasing our own tail. These systems aren't overly complex but they do seem temperamental at times. More often than not our problems are due to some small leak somewhere. In a plane it's probably less likely but still possible.

Chip-

Over charging is not the same as over pressure, two very different things.

Mike C.

The pressures are well within MM values.

Evaporators not freezing. No fog in the cabin.

I’m not sure what number you are thinking when you say high pressures, but there is a high pressure limit switch and blow off plug so the pressures can’t be really really high.

Mike C.,

How old is your compressor? When was the last time it was serviced? If the oil level is wrong or dirty the pistons will underperform. It’s not just about freon and pressures.

Could some of the components of the old Keith systems be upgraded under a field approval? I have to imagine there are a LOT higher performing and more efficient compressor and blower options available today.

For example:
https://duryeatechnologies.com/dc-air-c ... ectronics/

It would likely be tough to get a field approval, but easy to get DER approval

My system was converted to R134a in 2012 which was a new compressor and condenser assembly, so relatively young. It is an automotive part.

This was unexpected since the maintenance tracking said it still had the R12 system in it when I bought the plane. So I lucked out and had the R134a conversion I didn't expect.


Shortly after I bought the plane, I found the system setup all wrong. Wrong pressures, wrong balance, very poor performance, etc. It got carefully tuned and adjusted and now works decently. Also, all the evaporators fins were clogged with carpet dust. After 4 hours of carefully cleaning them, much better.

The freon system being way out of whack was one of many things wrong with my plane when I bought it. Almost all those things took very little money to fix, but took careful diagnosis to find the root cause. I don't think the Textron service center knew how to detect these problems or how to fix them without gratuitous part replacements.

Mike C.