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Old 05-28-2013, 07:16 AM   #1
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Roof top a/c heat pump problem

I have a Dutch Star 4320 with two Dometic 15,000 BTU a/c's. the front unit will not heat or cool. The fan and compressor run, but just will not do their job. I suspect low coolant, as the condenser is clean and the system moves air through the ducts. The unit does not cycle or trip circuit breakers. I have been told by an RV service center that coolant cannot be added to these units and if it is low on coolant, then replace it. I have read the maintenance manual for the unit and it speaks of purging and refilling the coolant as a fix for my specific problem in the trouble shooting chart. I realize that a technician needs to do this and if the unit leaked down once it might do it again, so there is potentially a leak to fix.

Has anyone had this problem and recharged their unit, or is it just cheaper and easier to replace it?
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Old 05-28-2013, 07:37 AM   #2
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Originally Posted by vraines View Post
I have a Dutch Star 4320 with two Dometic 15,000 BTU a/c's. the front unit will not heat or cool. The fan and compressor run, but just will not do their job. I suspect low coolant, as the condenser is clean and the system moves air through the ducts. The unit does not cycle or trip circuit breakers. I have been told by an RV service center that coolant cannot be added to these units and if it is low on coolant, then replace it. I have read the maintenance manual for the unit and it speaks of purging and refilling the coolant as a fix for my specific problem in the trouble shooting chart. I realize that a technician needs to do this and if the unit leaked down once it might do it again, so there is potentially a leak to fix.

Has anyone had this problem and recharged their unit, or is it just cheaper and easier to replace it?
Here is what a technician passed on to me:

These units are hermetically sealed at the factory and have NO PROCESS VALVES to allow the use of pressure gauges to determine the state of charge remaining in the unit. It is not economically feasible to add valves to these systems to " just give it a shot of FreonŽ". The process is as follows:

• Remove unit to bench
• Add piercing valves and vacuum out any refrigerant in the system (it is a Federal crime to knowingly allow the discharge of ANY refrigerant gas into the atmosphere. Fines are $10,000 per occurrence!)
• Remove piercing valves and solder permanent Schrader valves in their place
• Re-pressurize the system with nitrogen and dye to check for leaks
• Find and repair leaks if possible (If not possible, like a leak inside one of the could, you are done at this point and need a new unit)
• Evacuate any nitrogen and purge the system again with pure nitrogen and pressure test.
• Remove nitrogen after a positive pressure test and re-charge with appropriate refrigerant (R-22 or R-410A) in the quantities listed on the data plate
• Remove gauges and re-start the unit to test.
• Re-install unit with new gasket seals

Note* All of this is happening on a test bench AFTER the unity has been removed from the trailer. It must be re-installed after completion.

As I said, it is no longer cost effective to do all of this when you can get a new factory fresh unit with a warranty for the same or less than completing the above precess.
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Old 05-28-2013, 10:55 AM   #3
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Here is what a technician passed on to me:

(it is a Federal crime to knowingly allow the discharge of ANY refrigerant gas into the atmosphere. Fines are $10,000 per occurrence!)

Whoa, .......all those Airsoft Gun owners will become very nervous after reading that.

From Wikipedia on 134a AC refrigerant:

"Other uses include plastic foam blowing, as a cleaning solvent, a propellant for the delivery of pharmaceuticals (e.g. bronchodilators), wine cork removers, gas dusters and in air driers for removing the moisture from compressed air. 1,1,1,2-Tetrafluoroethane has also been used to cool computers in some overclocking attempts. It is also commonly used as a propellant for airsoft airguns."
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Old 05-28-2013, 11:18 AM   #4
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Before doing any of the above, I'd check the compressor Start Capacitor & replace w/a known good start cap. This is the most common fail part in your AC and would cause these symptoms except for the compressor motor running (i.e. my theory is that may be wrong, compressor isn't properly running). Start caps are about $20-25, and you should carry a spare anyway.

I'm guessing you'll find you start cap is 43-53 micro-farads @ 250V (I wouldn't replace w/one @ 120V, you could use one at 330V or 440V which are more heavy duty).
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