Air Conditioner Question

[Txbyker]

I have the factory A/C in my plane.  The air blows strong but the compressor cycles on and off, which alternates blowing cool air and un-cooled air.  Freon is at the proper level.  Any ideas where to look for potential issues?

Russ

[flyboy0681]

Wish I had that problem

[jaylw314]

Is it supposed to?  Most car AC's have a clutch that cycles them on and off depending on demand.  They have to work well at low or idle speeds, so they can't run constantly at cruising rpm's.  Of course, I don't know anything about AC's in aircraft, but I'm guessing if you get adequate cooling while idling and taxiing, there must be some kind of clutch

[Txbyker]

37 minutes ago, jaylw314 said:

Is it supposed to?  Most car AC's have a clutch that cycles them on and off depending on demand.  They have to work well at low or idle speeds, so they can't run constantly at cruising rpm's.  Of course, I don't know anything about AC's in aircraft, but I'm guessing if you get adequate cooling while idling and taxiing, there must be some kind of clutch

Yep, these look like OEM AC from Chrysler I hear.  The compressor cycles on for a minute then off for a while.  Of course, when on its cold.  But it is not cooling anything off.  It used to blow cold full time.  I dont think there is a thermostat.

Russ

[N231BN]

You need to have a set of gauges connected while it's running to see if it's tripping the high or low pressure switches. My guess is it's going high after a while which probably means the receiver/dryer is partially plugged.

[MARZ]

Hey Russ - I have a set of gauges if you want to throw em on.  I even know how to use them

Im thinking it may be a bit low - there's a low pressure cut off to protect the compressor when you don't have enough freon.

[Txbyker]

30 minutes ago, Mike Ropers said:

Hey Russ - I have a set of gauges if you want to throw em on.  I even know how to use them

Im thinking it may be a bit low - there's a low pressure cut off to protect the compressor when you don't have enough freon.

Thanks Mike.  No it’s full.  Something else seems to be causing the cycling.

[MBDiagMan]

How did you check the refrigerant level?  Short cycling is an indication of low refrigerant level as is decreased cooling capacity.  Why are you so sure it is full?  What are the pressure readings with the engine running above idle and the ambient temperature at that time.  It would be helpful also to know the temperature at the vent.

Edited August 9, 2018 by MBDiagMan

[Txbyker]

15 minutes ago, MBDiagMan said:

How did you check the refrigerant level?  Short cycling is an indication of low refrigerant level as is decreased cooling capacity.  Why are you so sure it is full?  What are the pressure readings with the engine running above idle and the ambient temperature at that time.  It would be helpful also to know the temperature at the vent.

IA was connected to the port in the tail while I ran the engine at 1500 rpm with the AC on.  

Thanks

[MBDiagMan]

If he was only connected to the high or low, you cannot determine proper charge.  You must monitor both high and low pressures and temperatures to confirm proper charge and operation.  You need someone well versed in refrigeration.  For even the very best aviation mechanics, refrigeration is rarely in their area of expertise.

[Jerry 5TJ]

What type refrigerant?

What pressure and sub-cooling temperatures do you see during the time when compressor is running?

Agree with other posts that a single pressure reading won’t tell you the system performance.  

To be picky—you most likely need to possess an EPA 609 certificate to do any of this legally.  

 

 

[MARZ]

There's a couple things that would lead to the compressor cycling excessively - the only way to diagnose what's really going on is to monitor both pressures as the system cycles. (Yes I'm certified)  I'm a "start with the easy stuff first guy" so here's some thoughts. 

Low Pressure Cutout - in order of likelihood

• System undercharged - a result of a leak in the system 
  • If you go from a normal system to a cycling system start here. 
  • If you go from a cycling system to no A/C your quest is complete - you have a leak somewhere in the system.
• Plugged orifice - expansion valve (system internals coming apart
  • If you are getting near normal cold when the compressor is running - discount this item 
• Faulty switch
  • Kick out at predetermined pressures - if the pressure at kickout is correct - discount this item

High Pressure Cutout - in order of likelihood

• Condensor airflow blocked (dirty fins)
  • Look for clogged fins 
• System overcharged
  • Unlikely as I assume this has just reared it's ugly head without other contributing circumstances
• Plugged orifice - expansion valve (system internals coming apart)
  • If you are getting normal cold when the compressor is running - discount this item 
• Faulty switch
  •  Kick out at predetermined pressures - if the pressure at kickout is correct - discount this item

Faulty cabin temp sensor

• If equipped - the sensor that controls the cabin temperature 
  • when reaching the predetermined temp this will cut out the compressor.

[Jerry 5TJ]

Ok, say he has a leak (my guess, too).

What is the best way to locate the leak?  Pressurize with nitrogen & look for bubbles?   Something more sophisticated?  

[MARZ]

An electronic leak detector.  

Freon acts like a roughly like thermometer - the hotter it is the higher the pressure - you can expect @90 psi on an at rest system with a 90 degree ambient air temperature.

So you hook a gauge and see if you have any pressure - test all the connections at rest.  Another tell tale is that the freon carries lubricating oil - a leak will accumulate dust/dirt in most instances.   

Some folks swear on the fluorescent detection additive - but I won't use it, never had much luck with it. 

[N201MKTurbo]

It most likely isn't an expansion valve system (TXV) but a CCOT (Cycling Clutch Orifice Tube) system. Most auto air-conditioners use this system. It will cycle the clutch according to the system pressure. If your sub cooling is not correct it could be short cycling. Just filling it up with refrigerant isn't necessarily the correct thing to do.

https://www.freeasestudyguides.com/ac-cycling-clutch-orifice-tube.html

I'm not an air conditioning professional, or certified, but I've never met an air-conditioner that I couldn't fix.

 

[Txbyker]

I have been puzzled by my AC issues.  But I think I have found a cause indicated by data.  The pressures of the system seem ok, fans blow well, etc.  First, some more info...the AC stopped blowing cold after my annual.  At annual I had the alternator rebuilt per 500 hr spec.  Also, I had the autopilot fan replaced.  During this work some chaffed wires arc'd against the frame where they were tie wrapped and fried my voltage regulator.  That was replaced and wiring fixed.  But in reviewing my post annual Savvy Analysis flights I notice my amp draw is now flat lined.  Prior to this arcing issue, AMPs would show +20 during AC operation and 0-1 when AC is off.  So, question is, assuming the arcing and voltage issue fried something causing the AC compressor clutch to not engage now, where is a pilot to look?

Russ

[Yetti]

There are going to be a couple of wires on the compressor that engage the clutch.  By the fan belt.  Start there. trace them back.

[MBDiagMan]

I am confused.  In the original post it was stated that the compressor was cycling.  The compressor can’t cycle without power.

Also, how can you know the pressures are okay if the clutch has no current draw?

[Yetti]

The compressor could cycle if the wires to the clutch are flaky/shorting.   Could possibly have a auto reset circuit breaker.....

[Txbyker]

2 hours ago, Yetti said:

The compressor could cycle if the wires to the clutch are flaky/shorting.   Could possibly have a auto reset circuit breaker.....

Kelly, I think it’s the evaporator fan relay but good suggestion.  That breaker was ok.  Put a multimeter on the relay and it tests bad.  I was informed it is the evaporator fan that creates such a draw on the battery, not the compressor as I had thought. So no draw means no fan.

Russ

[Yetti]

fans draws many amps

 

[Txbyker]

Fixed.  I am posting this in case future MooneySpacers have the same issue.  Symptom - cockpit fans blow.  Air starts cool, then turns to ambient if not warm.  Freon and pressures normal.  AMP draw is nominal.  Issue - Blower fan that cools the recirculating freon in tail not operating.  Fix - measure voltage of relay located under blower breaker in tail. Check fan voltage and check bus voltage to relay with switch on and off. Kissling part number 26.72.03 price $179.  

Russ

[mike_elliott]

33 minutes ago, Txbyker said:

Fixed.  I am posting this in case future MooneySpacers have the same issue.  Symptom - cockpit fans blow.  Air starts cool, then turns to ambient if not warm.  Freon and pressures normal.  AMP draw is nominal.  Issue - Blower fan that cools the recirculating freon in tail not operating.  Fix - measure voltage of relay located under blower breaker in tail. Check fan voltage and check bus voltage to relay with switch on and off. Kissling part number 26.72.03 price $179.  

Russ

Russ, did you find this fix or did DMAX? Great troubleshooting!

[Txbyker]

45 minutes ago, mike_elliott said:

Russ, did you find this fix or did DMAX? Great troubleshooting!

Mike, admittedly, it was a combination of Brian Kendrick and Savvy Analysis. Brian debugged with me over the phone but it was the AMP draw revelation that helped me figure it out.  I checked Savvy past flights and noticed the AMPs went flatline after the annual this year.  The AMP draw on the G-1000 where it adds 20+ during A/C operation is purely due to the big fan blowing in the back sucking air through the bottom vent that A/C planes.  Savvy does a nice job of charting voltages in addition to CHT and EGT as you know.  I was incorrect in thinking it was the compressor clutch turning that draws AMPs.  

Russ

[mike_elliott]

3 minutes ago, Txbyker said:

Mike, admittedly, it was a combination of Brian Kendrick and Savvy Analysis. Brian debugged with me over the phone but it was the AMP draw revelation that helped me figure it out.  I checked Savvy past flights and noticed the AMPs went flatline after the annual this year.  The AMP draw on the G-1000 where it adds 20+ during A/C operation is purely due to the big fan blowing in the back sucking air through the bottom vent that A/C planes.  Savvy does a nice job of charting voltages in addition to CHT and EGT as you know.  I was incorrect in thinking it was the compressor clutch turning that draws AMPs.  

Russ

great info. Brian and Savvy are great, as was your tenacity to resolve it and just not resign yourself that "AC's in Mooney's su@k" as so many have.