Question on the air cycle machine

[MatzeH84 81]

I noticed that the warning panel now also has an indication light for the air cycle machine (FREON ON), but when selecting COOL on the COOL/FAN switch this light does not illuminate.. in fact it never does, only when powering up from C&D. Shouldn't it be on with the switch set to COOL?

[ark 1,291]

2 hours ago, MatzeH84 said:

I noticed that the warning panel now also has an indication light for the air cycle machine (FREON ON), but when selecting COOL on the COOL/FAN switch this light does not illuminate.. in fact it never does, only when powering up from C&D. Shouldn't it be on with the switch set to COOL?

Yes and No!

Yes:  The Freon light should be on when the Cool/Fan switch is in the Cool position.

No: The Freon light is not currently implemented except as part of the overall panel light test system. That is, it comes on with ALL the other lights but there does not seem to be a Lvar that represents it individually (will confirm this with Mark at FSW).

Our resident Lear35 pilot, Joe, tells me early Lear35s did not have a Freon light, and when I checked earlier versions of the FSW Lear there in fact is no Freon light on the annunciator panel,  which I assume explains why there is no individual variable for it at this time. So we just have to consider it NO OP. Joe also pointed out that the Freon light in the actual aircraft just indicates the position of the Cool/Fan switch. With the switch in the Cool position the light will come on even if the air conditioner is not working (assuming you have at least battery power). I noted the air conditioner is not supposed to be on until the engines are running, so I guess the purpose of the light is to warn you if it is on before engine start.

 

Al

Edited August 16, 2019 by ark

[MatzeH84 81]

Thanks for the update! 🙂

[capceo 117]

The real purpose of the FREON ON light is to remind you that it's on, so you remember to turn it off before you climb through its limiting altitude. On early airplanes it was FL180, on the later airplanes, it was FL350. Naturally, the two 35A's I fly at work have two different limits, so I constantly have to think about which airplane I'm on as to when the AC needs to come off.

 

Also worth mentioning is that the airplane doesn't actually have an air cycle machine. It's a plain old electric air conditioning system. The Lear doesn't have an APU, so if it did in fact have an ACM, the only way to run the AC would be to run an engine, since an ACM uses bleed air to provide hot or cold air. The advantage to having electric AC is that we can run the AC on any source of power that provides 28VDC. In other words, we can run it using one engine driven generator with an engine running, or we can run it off a GPU.

[MatzeH84 81]

Yep, I already understood all this.. I guess the problem was the language barrier, I'd better have called it an AC unit or something instead of ACM. Should be an easy fix though, to bring this light to life and add another thing to look after. Not that it is necessary, but as the light is already there.. why not use it. 😉

[ark 1,291]

1 minute ago, MatzeH84 said:

Yep, I already understood all this.. I guess the problem was the language barrier, I'd better have called it an AC unit or something instead of ACM. Should be an easy fix though, to bring this light to life and add another thing to look after. Not that it is necessary, but as the light is already there.. why not use it. 😉

That might be something Mark will consider the next time the Lear is updated, maybe around FMC update time. 🙂

[richjb2 195]

Just to clarify, the Lear 20, 35, 55, 31/31A, and 60 series do not have air cycle machines.  Bleed air is taken off both engines and routed through a heat exchanger that only works inflight to cool the air by air drawn in through the dorsal fin inlet before it goes into the cabin.  The heat exchanger does not work on the ground.  Only hot bleed air would be pumped into the cabin on the ground, hence the use of a freon air conditioner system. 

In warm temperatures, pilots leave the Cabin Air switch OFF during taxi out and turn it on just prior to takeoff.  The older Learjet checklist (the "candy checklist" because they were colored green, yellow, and red) had the Cabin Air Switch check in three different places, Before Taxi, Taxi, and Before Takeoff.  It was the "3 strike" check, because if you missed it the third time, you took off with the Cabin Air Switch "OFF" and had no pressurization.  In 1998, Learjet introduced the new checklist with much less steps.  Cabin Air Switch was only on the Before Takeoff checklist. 

Rich Boll

[ark 1,291]

14 hours ago, richjb2 said:

Just to clarify, .........

An interesting bit of Learjet history -- thanks.

Al

Edited October 31, 2019 by ark