Dash Air Conditioner hates me

[CapnDean]

Bought the coach 2 years ago.  Previous owner had given up on the dash air after having it in the shop 3 separate times.   Each trip he left with cold dash air.  But within 30 days or so.....  no dash air.   Each time he returned to the shop, the freon charge was waaaay low.  For sure it was a leak, He got tired of paying the shop a few hundred bucks to recharge it and look for a leak.

I bought the coach and took it to the shop that works on my Big truck.   Explained to them:  Its a leak, we just gotta find it.   The coach passes the machines leak test, but the dye tells a different story.  We have replaced the dryer, replaced the condensor, replaced the evaporator, replaced the expansion valve and a couple of hoses that had a slight amount of dye on them.   Now mind you that each of these replacements has included a complete vacuum down of the system and a recharge.  (this is in excess of 10 trips to the shop) - even one instance the brand new condensor leaked! (warrantied no problem).   Each time I leave the shop, I have cold air, only to find a month or so later that I do not.

This last trip to the shop, the coach held a vacuum on the system overnight with no loss.   I was ecstatic.   We left to go on a trip, had cold air for about 10 minutes and then I can hear the compressor pressure relief valve blasting out freon.    Back at the shop.....  the system has lost all its charge again- - there is dye all over the compressors relief valve.  vacuum the system down again, charge it back up properly.... and we are seeing pressure that is too high indicating poor airflow across the condensor or an obstruction somewhere in the system.   I am as stumped as the technician is.  I believe that perhaps we have clogged the system with dye somehow?   My coach is side radiator and the hydraulic fan pulls plenty of air across it.    Essentially the entire system is new with the exception of the compressor and the long lines from the evaporator.  (Absolutely no dye on any).   I am stumped.

[Harvey Babb]

I would suspect an intermittent blockage of the high pressure line going from compressor to condenser, or of the condenser itself. Unless the system is severely overcharged there should be no way to reach high enough pressure to blow the relief valve, as there should be enough space in the condenser to accommodate all the liquid refrigerant. About the only way I can think of to troubleshoot something like this would be to add pressure test points at junctions in the high pressure side. There is normally already a test port at the expansion valve and at the suction of the evaporator. Perhaps make up some fittings to add test ports on both sides of the condenser.

I have seen a hose with a leak in the liner that did not leak externally but instead collapsed the liner, blocking flow. On releasing pressure the refrigerant would leak out of the space around the liner, "healing" the blockage, only to have it inflate and block the line again after things got flowing again. That falls squarely in the "freak occurrence" column,  but it did happen..

Best of luck! I think you'll need it.

 

[Oregon04Windsor]

Has the compressor been replaced?  I spent many years working on RV chassis and the a/c compressor is a common source of leaks and a tough one to spot.  I think when under pressure or vacuum the shaft seal may hold but then leaks out as the compressor cycles.  If the bearings are worn you will get compressor vibration which could lead to leaking.  I'd zero in on that compressor.

 

[MyronTruex]

If the compressor was leaking I suspect the dye would get blown away so you may not detect it there.

 

[Chuck B 2004 Windsor]

The problem happens when you turn on the dash air before the cooling fans that pass air through the evaporator are not running making the high Freon side Freon get too high.  That causes the Freon to leak.  The solution is to not turn on the dash air until the coolant temperature gets warm enough to turn on the fans.

Chuck B 2004 Windsor

[vito.a]

Does your coach use the Sauer Danfoss electronic controller on the hydraulic driven fan, or the mechanical wax valve controller?

Are they placing a large box fan near the radiator when servicing the A/C system?  When the coach is sitting static the engine does not develop enough heat to command a high enough fan speed for the A/C system.  

For what its worth, on the Signature model Monaco mounted the A/C condenser behind the front axle against the firewall with an electric fan.  This placement seems to work much better. 

Hope you get it figured out.  

[Guest Ray Davis]

Chuck and Vito may be on the right track.   I think Chuck misspoke saying the evaporator when he may have neant condensor.  Anyway they are both saying on some coaches the hydraulic engine fan is also your air cond fan and it does not move nough air until the engine is working hard enough to need cooling, by that time the    pressure in the air cond might be high enough to pop the compresor relief valve.

This is theoretical as I have never had this happen but have heard of it.  You could also have a defective pressure relief valve.

[TimSpencer]

The fan on the condenser is going to be your issue. As soon as you turn on the dash air the condenser will need full air flow. Best way to ensure that is to have a separate fan just for the dash A/C condenser. If you had an obstruction in the system the pressure would level off and compressor would cycle off on low pressure once the refrigerant was stacked up behind the obstruction. Personally I would add an electric fan attached to the a/c condenser and have it triggered by the clutch on the compressor (going to need a pilot relay).  Derale and others make inexpensive and powerful models. Or add a high pressure cutoff switch to prevent compressor from reaching blow off/ relief pressure. Or better yet both for added security 

[John Harris]

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.

[TimSpencer]

Most compressors have an internal relief. If discharge pressure is to high it bypasses to the low side. Makes an odd whoosh noise. Hoses can definitely leak. Soap bubbles, refrigerant detector, dye, etc can be used 

[dl_racing427]

Were all these parts replaced at the same time, and did you do a complete flush of everything not replaced with denatured alcohol?
Any debris circulating in the system could quickly clog the new expansion valve.

Also, your fans should be going to high speed whenever the A/C is turned on. 

My 93 Dynasty has the condenser on the side opposite the radiator, with dedicated electric fans.
I always thought it made more sense to put it up front like the Sigs.

[TimSpencer]

Alcohol is not the “best” line flushing agent. It can attract water. There are line flushing chemicals available that do a better job. Be sure to disconnect  or bypass the metering device and compressor before flushing and always blow out flushing chemicals with nitrogen. Always use nitrogen to pressurize and leak check as well. Take some time to leak check it will pay off in the long run. 

[Chargerman]

When I first bought our Coach the dash A/C didn’t work. The guy that I first brought it to to charge it quickly determined it was a bad compressor. He also said there was a lot of crap in the lines and thought I would need a new condenser also. He said to remove the dryer and the lower line off of the condenser. Then get a few cans of brake cleaner spray a bunch in a line and blow it through with compressed air. I did that a bunch of times to both line until clean. Then installed a new dryer and compressor and brought the Coach back to him to charge the system. That was seven years ago and it still blows cold air today. 

[Ivan K]

Whatever works for you but there is a liquid made just for that and you can rent the pressurized tank at O'Reilly for free.

[Chargerman]

Good to know. Thanks

[dl_racing427]

13 hours ago, TimSpencer said:

Alcohol is not the “best” line flushing agent. It can attract water. There are line flushing chemicals available that do a better job. Be sure to disconnect  or bypass the metering device and compressor before flushing and always blow out flushing chemicals with nitrogen. Always use nitrogen to pressurize and leak check as well. Take some time to leak check it will pay off in the long run. 

Agreed, but it's cost effective.
I bought a pressure flush system and I've used denatured alcohol on two systems so far with good results.
Of course I do this with the compressor and orifice removed, and back flush everything until I get clear alky.
Then I blow it out with dry shop air and pull a vacuum on the system overnight before adding oil and recharging, which should boil out any residual moisture.

[TimSpencer]

Moisture is the toughest thing to remove from A/C systems. This is why nearly all systems include a filter/drier. Nitrogen can help to dry systems. But sometimes it takes a couple times of alternating nitrogen the deep vacuum. Anything that holds or attracts moisture should be avoided if possible. It seems these systems get neglected since there are alternative cooling systems. I have not used this brand but it’s very similar to the Calgon setup I use. 
https://www.amazon.com/HVAC-Guys-System-Flush-Refrigerant-Based/dp/B09XG6X77M

[det944]

Just a thought, most automotive systems have hi and low pressure switches to protect the compressor by shutting it down at specific pressures. Not sure MH systems would be different but a failed high pressure switch would allow the compressor to provide pressure that exceeds the system design, allow actuation of the pressure relief Valve as a secondary fail safe to protect the system. Unfortunately this results in refridgerent loss. May want to see if there is a hi pressure switch in the system.

[TimSpencer]

Most automotive systems use a low pressure switch only. A high pressure switch could be helpful but not always installed 

[David Pratt]

For the norm the Receiver-Drier is going to be mounted close to and in the Vicinity of the Condenser. The Receiver Drier is always installed on the High-(Pressure) side of the AC system. The High Side-(Pressure) of the AC system can be identified by the larger outside diameter hose. The low pressure side-(Suction) will normally be the smaller outside diameter hose.

The Dash AC systems that are installed in our coaches is very similar to the Automotive AC systems installed in most Ford Automobiles from the Sixty's thru the Ninety's. They consist of a Evaporator, condenser, evaporator fan motor, condenser fan motor, compressor, receiver-drier, dash controls-(either electronic or vacuum operated), Expansion valve, Evaporator thermostat, fan speed control resistor block and a low pressure compressor cut off switch. On coaches built after 1994-(when the switch was made to R134), they stopped using only a low pressure switch and went to a Binary or a Trinary Switch. The Binary Switch still has two wires attached, but the switch internally has a low pressure and a high pressure switch internally. The Trinary Switch will have three wires attached to it. It still functions the same as the Binary Switch with the addition to also providing power to the condenser fan motor when required in most new automotive systems.

The Condenser will have a smaller OD hose and a Larger OD hose connected to it. If you are having trouble finding the Receiver-Drier follow the smaller OD hose from the condenser and it should take you to where the Receiver-Drier is mounted. The Expansion Valve will be installed in the outlet side-(Low Pressure) at the Evaporator and the Low Pressure Switch will also be installed in the Suction side of the system and is normally installed close to and after the Expansion Valve. The Expansion Valve's function is to change the Freon from a gas back into a liquid after it passes thru the evaporator.

If your system has been out of Freon because of a leak in the system you should always replace the Receiver-Drier and evacuate the system after repairs have been made. The Receiver-Drier is the filter in the system and is the primary defense in keeping the system from contamination. If the AC system has been open for any length of time because of a leak  the receiver-drier will pull in whatever moisture and crap from the atmosphere and will plug it up. It is very rare to find an expansion valve plugged up unless you had a compressor failure that contaminated the system.

I will now let the experts chime in!

Edited October 28, 2022 by David Pratt
Corrected hose information.

[Ivan K]

Well, reluctantly I must admit that I am confused by some of the info, maybe I read it wrong. Like the suction line size vs high side line size and the expansion valve function.

[dl_racing427]

10 hours ago, Ivan K said:

Well, reluctantly I must admit that I am confused by some of the info, maybe I read it wrong. Like the suction line size vs high side line size and the expansion valve function.

Mr. Pratt has a couple errors in his description.
The smaller line is usually the high side carrying hot gas from the compressor to the condenser.
The condenser gives up heat to the outside air,  cooling that hot gas and condensing it into a warm liquid, which then travels through the expansion valve or orifice tube, which drops the pressure, and consequently the temperature of the liquid, and sending it into the evaporator.
The evaporator absorbs heat from the air inside the car, and the liquid evaporates into a cool gas, before heading to the accumulator/drier and back to the compressor, which raises it's pressure and temperature and starting the cycle over.

Most systems have a low pressure switch which cycles the compressor based on the pressure at the accumulator.  This is done to prevent overcooling the evaporator and freezing it up.  It also prevents the compressor from engaging if the system is low on refrigerant.
Some systems also have a high side pressure switch, but many do not.
More modern systems, which use the engine ECU to control the compressor and fans, may have a pressure sensor instead of a switch to provide feedback to the ECU.

Of course, there may be some variatons in systems, but this is basically how every system works as far as the flow and phase change of the refrigerant.

[TimSpencer]

David has it correct. Lots of variables depending on the designer of the system but automotive and RV systems are fairly basic. Receiver/drier has to be on the liquid line as it stores a bit of excess refrigerant and filters the refrigerant. Liquid is metered through the expansion valve into the evaporator. The liquid is vaporized lowering its pressure and it then can absorb heat from the air coming across the coil. This vapor then returns to the compressor. The compressor compresses the gas raises its pressure and corresponding temperature. This hot gas is then sent to the condenser where the heat is transferred to the air coming across the condenser coil and condenses the gas back to a liquid. And the cycle repeats. Line sizes in automotive systems can be tricky as the rubber hose outside dimensions don’t always give an idea of the actual inside dimension. But at the compressor the larger “cooler” line is the suction line from the leaving side of the evaporator the liquid line from the condenser to the expansion valve/evaporator is much smaller and the discharge”hot” line from the compressor to the condenser will be somewhere in between the suction and liquid lines. I’ll look for a pic to show a refrigeration system. 

[David Pratt]

Most, if not all the Class A Motor homes that have the aftermarket Dash AC systems, such as SVS, Frigette and others do not use an Accumulator. Instead they use a Thermostat mounted on the Evaporator Assembly that has a capillary tube that protrudes into the evaporator and will cycle the compressor based on the temperature of the evaporator coil to prevent it from freezing up. This thermostat functions basically the same as the Accumulator except it relies on temperature instead of pressure. If you have the Wiring Diagram Manual for your coach it should have the schematic for the AC System that is in your coach which can help you to understand the flow of the system and its components.

The Class C and other RV's will differ from the above basic system because the Dash AC Systems are the Manufacturers Automotive System and the components can vary along with their functions, but the basics of the systems and operation are the same.

Another issue that has not been discussed very much is the fact that R134A Freon is going to be phased out because the new Climate Change Initiative and will no longer be available in a few years. The new Freon replacement is Designated as R123A. The Automotive manufactures started installing the new Freon in their vehicles after 2020. This new Freon is not available to the Public yet and is also very difficult for the Dealers to purchase. You may want to stock up on a supply of R134A for the future. The cost of R134A has tripled in the past six months. R134A Freon has no shelf life and can be stored until needed.

[Ivan K]

Yeah. EU has outlawed R134 in new cars a good while ago. Usually only matter of time for EPA to do same.