Dash Air Conditioner hates me

[Tom Cherry]

Curiosity from a layman, but have had a small leak for years and the OTR shop usually adds a canister or two of Freon to my system every 3 years or so.  Pastime, a friend who is a graduate EE, but retired when he sold his electrical system and was bored and two several HVAC courses at our tech school and does courtesy repairs on his kids and neighbor’s cars and his beach houses and such.

He added 2 cans or canisters last year and it works about the same as new…..which is the case when the shop did a “recharge”.

as long as the leak is controlled and you have more Freon added, that is the approach that I believe was advocated here.  Now, it may be necessary to purge (release the Freon into a recycling unit) and then pull a vacuum and totally refill if things gets worse.  But as long as you add a small amount every few years….live with it.

What I am confused with, assuming the evaporator and the blower are OK then it is not necessary to go inside the unit….which is a PITA.

Is the receiver/dryer the “metering device” in the diagram and is it located outside the HVAC box so it can be serviced or replaced without major surgery.

Thanks….

[Ivan K]

1 hour ago, Tom Cherry said:

Is the receiver/dryer the “metering device” in the diagram and is it located outside the HVAC box so it can be serviced or replaced without major surgery.

The simplified diagram above appears to be of a domestic HVAC system and what may look like a receiver/dryer is just a thermostatic expansion valve.  On most recent automotive style systems I have worked on, the expansion valve has 4 ports, is mounted directly to evaporator hard lines and the temperature is taken inside of it as the evaporated gas leaves the evaporator, instead of the pictured remote capillary sensing. Regardless of which one is used, every one I have seen is outside of the evaporator/heater box. Does not mean it is always easily accessible,  mine is inside under the dash, PITA.

[David Pratt]

The Dash AC system in our Coaches hold a lot of Freon. They are the approximately the size of a 1.5 ton AC Unit. and hold anywhere from 40 to 60 ounces of Freon. You have hoses that run the entire length of the coach. Most hose failures occur in the area of the fittings unless the hose has been rubbed through or chaffed by a chassis component or improper installation. another area of a potential leak is the AC compressor shaft seal.

It is not uncommon to have to add a small amount of Freon to keep the system fully charged and operating at it's best. Check the hoses for any chafing and inspect closely the area around the fittings. If you detect any sign of an oily residue it is a sign of a leak. The older AC hoses had a tendency to become porous as they age and will show these signs. The newer hoses are manufactured much differently and prevent the hose from becoming porous. Seals in the compressor will also leak slightly as age sets in. It is very difficult to prevent this and the best way to stay on top of it is to annually have the system inspected, the pressures checked and add Freon as necessary to top the system off.

AC systems should be exercised as much as possible. They do not like being OFF.

As long as the AC system stays closed and is operating normally just add Freon as needed. You may also want to add a dye into your system the first time you have to add Freon. With the Dye in the system you will be able to detect a leak or potential failure using an Ultraviolet light. The Dye used for the AC systems is a very small amount and will not hurt the system.

There are also some very good Sealers on the market today that will seal off any small leaks that may show up in the AC system, such as Evaporators, Condensers and other components. When properly added they live in the system, will not harm the system and if a small leak were to develop may and can stop it.

I have four Coleman MACH8 Roof Top AC Units on my ih-45. The rear unit failed due to a leak in the evaporator. I installed a schrader valve in the system and recharged the unit. It leaked down again within about six months. I decided to evacuate and flush the system with Nitrogen, recharged it and added a stop leak into the unit. That was two years ago and the Unit is still working and cooling great and no leaks. The sealer is used through out the commercial refrigeration business and is called PROSEAL XL4. It is compatible with R134A and R410A and other Freon systems. You can purchase in various amounts to service AC units from 1.5 tons to 5.0 tons. When used properly it will not harm the system or the compressor.

The receiver-drier, expansion valve, pressure switches and thermostat are all installed outside of the Evaporator case and normally in plain site.

I keep a AC thermometer stuck into my center AC outlet in the dash so I can observe the temp coming out of the duct. The outlet temperature will vary based on the ambient temperature inside the coach on recycle mode. I travel with the front and rear roof airs operating and the thermostats set at 76 deg. The dash outlet temp was always between 49-55deg when the outside temperature this summer was 105 deg.

I added approximately 4.5oz of Freon to my system when I serviced it this year. This was a bit less than what I added to the system when I serviced it last year. This is another indication that the system is still tight and operating normally.

[cbr046]

I found a bracket rubbing on a refrigerant hose for the ISC engine, up top near the intake air hose / pipe.  Access through the hatch.  Y'all might look for something similar next time you're in there. 

- bob

[TimSpencer]

I would do exactly what the last couple posters suggested. Top off the charge if leak is small and frequency to top charge doesn’t increase dramatically. Taking into account that it will leak while in storage or on the road. 

[Guest Ray Davis]

The mechanics of refrigeration is often mystifying, so this site may help

The Refrigeration Cycle | HowStuffWorks 

The explanation uses Ammonia which is a great refrigerant but it's also very dangerous.  Our gas RV refrigerators still use ammonia.  There is an explanation of how those work at the link above.    I can remember when cities would have an ice plant that had huge compressors, they resembled a big old steam engine.    Those systems used ammonia as did a few buildings.  A leak would require the whole neighborhood to be evacuated.  The ice plant turned out huge blocks of ice that were divided into manageable sizes then delivered to stores etc.  I remember going to the ice plant with my dad and seeing those huge blocks come sliding down a ramp.  We had them grind some for us so we could make homemade ice cream.  Those were the good old days because I was too small to crank so my older brothers got the job. I sat on the freezer to hold it steady while they took turns cranking. Now we mostly buy Bluebell

Edited October 29, 2022 by Ray Davis

[CapnDean]

Oh heck no.  You think I can sleep knowing that the freon is leaking out on me?  The hateful AC unit has been repaired!   Throughout the process, everytime we found a leak, we replaced that component.  I sat down with my service tech and had a nice long talk.   He said "The only think we HAVENT changed.... is the compressor" - - Welp Guys......  It was the compressor.      I have good cold dash air and have made 90 days without losing freon!     Just goes to show you that you CAN pump enough money into it to fix it.

 

 A side note for those of us with SIDE radiators.   If you are running the coach from cold Iron and are only Idling  - - switch your dadh AC off.   Here's why....    I forced mine into overpressure by doing this and the relief valve blew and discharged a pile of freon.   It seems that at Idle our coach will take quite a long time to reach operating temp.  Until it does that, the hydraulic cooling fan wont kick on.   If that fan isnt flowing air across the radiator (and the condenser of course) if you run long enough the pressure will rise and psssssst out your juice.   

 

[TimSpencer]

Good to know the sequence of operation. I would add a small electric fan for the condenser to prevent “forgetting” to shut off the dash air. Could be triggered by the radiator temp or just on when A/C is one. Great to hear you located and fixed all your refrigerant leaks. To bad you had to replace the compressor. 

[dl_racing427]

9 hours ago, TimSpencer said:

Good to know the sequence of operation. I would add a small electric fan for the condenser to prevent “forgetting” to shut off the dash air. Could be triggered by the radiator temp or just on when A/C is one. Great to hear you located and fixed all your refrigerant leaks. To bad you had to replace the compressor. 

Best to power the additional fan with a relay from the A/C compressor clutch.
Interestingly, my 1993 Dynasty has the A/C condenser on the opposite side from the radiator, with it's own electric fans.

[Mondyndia]

On 10/21/2022 at 11:46 AM, John Harris said:

I have the same problem on my 06 Dynasty Diamond IV.  Condenser, compressor and dryer are all new and the evaporator checks out good. Can Someone tell me where the compressor relief valve is located. Also has anyone ever had a leak in the lines from the compressor to the evaporator and if so, how was it discovered.  Thanks, Jonh Harris.

Josh,

I have an 04 dynasty, bought it 6 months ago. Upon purchase the dash ac was adequate at best but not impressive but 2 months after purchase it quit blowing any cold air, had to open the window and thought i heard my engine compressor cycling, the gauge confirmed this so I pulled over to hunt for the air leak. Found a small hose, probably .25" od had pulled out of the round black sphere in the generator compartment. This is a vacuum hose that i assume engages the ac compressor. I cut the cruddy end off and reinstalled the hose and now the dash ac blows nice and cold. Don't think I would have found it if the hose hadn't pulled all the way off, dumb luck i guess.

[David Pratt]

There is no compressor relief valve installed in you AC dash System. There is a pressure switch installed that is discussed in detail in a prior post on this thread. On your coach it my be a low pressure switch that will cut the power to the compressor if the low side of the system gets below 20psi. It may also have a Binary Pressure Switch which includes a low and a high pressure cut off switch and will cut the compressor off below 20+/-psi or if the pressure exceeds 375+/-psi on the high side.

[dl_racing427]

14 hours ago, Mondyndia said:

Josh,

I have an 04 dynasty, bought it 6 months ago. Upon purchase the dash ac was adequate at best but not impressive but 2 months after purchase it quit blowing any cold air, had to open the window and thought i heard my engine compressor cycling, the gauge confirmed this so I pulled over to hunt for the air leak. Found a small hose, probably .25" od had pulled out of the round black sphere in the generator compartment. This is a vacuum hose that i assume engages the ac compressor. I cut the cruddy end off and reinstalled the hose and now the dash ac blows nice and cold. Don't think I would have found it if the hose hadn't pulled all the way off, dumb luck i guess.

Wish I could have problems like that. LOL
Glad you found it so easily.

[CapnDean]

In my system we found leaks in the condenser- replaced it, found leaks in a hose, replaced it, found leaks in the evaporator - replaced it.   Replaced the thermal expansion valve and the air dryer. Continued to lose freon.   We inspected the lines from the compressor all the way forward to the evaporator with the system charged with dye.   Every time worrying that the leak that we could not find, was in fact a ruptured line that we could not see. In the end it wasn’t - the compressor was the ticket.   Mind you that the coach always passed the vacuum test that the ac machine put on it.   But we never asked it to hold a vacuum overnight or any duration over an hour.   
 

my unit has an over pressure “pop-off” valve.    It has blown due to over pressure twice.   Both occasions it was my fault!   I started the Coach cold and let it idle while i replaced the air bag control valves.    I left the dash air running and the main never achieved the temp needed to light off the hydraulic fan (i have side radiator and condenser) no cooling air flow caused over pressure and the relief valve relieved.    Wife thought it was smoke and shut the motor down.      Good thing I had dug a trench…..    i had an air bag valve out and a quickly escaping air supply to deal with.

[dl_racing427]

20 hours ago, CapnDean said:

In my system we found leaks in the condenser- replaced it, found leaks in a hose, replaced it, found leaks in the evaporator - replaced it.   Replaced the thermal expansion valve and the air dryer. Continued to lose freon.   We inspected the lines from the compressor all the way forward to the evaporator with the system charged with dye.   Every time worrying that the leak that we could not find, was in fact a ruptured line that we could not see. In the end it wasn’t - the compressor was the ticket.   Mind you that the coach always passed the vacuum test that the ac machine put on it.   But we never asked it to hold a vacuum overnight or any duration over an hour.   
 

my unit has an over pressure “pop-off” valve.    It has blown due to over pressure twice.   Both occasions it was my fault!   I started the Coach cold and let it idle while i replaced the air bag control valves.    I left the dash air running and the main never achieved the temp needed to light off the hydraulic fan (i have side radiator and condenser) no cooling air flow caused over pressure and the relief valve relieved.    Wife thought it was smoke and shut the motor down.      Good thing I had dug a trench…..    i had an air bag valve out and a quickly escaping air supply to deal with.

Glad you survived.  NEVER, EVER get under a coach supported by either air suspension or hydraulic jacks.
Make sure it's supported by properly rated jack stands under hard points on the chassis.

Congrats on finding your A/C leak, they can be elusive.

[Guest Ray Davis]

On 11/16/2022 at 8:49 PM, CapnDean said:

Good thing I had dug a trench…..    i had an air bag valve out and a quickly escaping air supply to deal with

This trench,  was it a trench you drove the coach over sort of like a pit?

Who would have expected that series of events, it shows you just can't be too careful, especially under the coach.

BTW, I have placed an elect fan blowing over my side radiator to guard against high head pressures.