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Dash a/c charge amount


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I have a 2007 diplomat. The low side schrader valve leaked part of the charge out. Had the system evacuated the rest of the way-pulled out 22oz.  Replaced high and low valves, and vacuumed system down. Sticker says 52oz r134. At 52oz, low side was 15psi and high side was 55psi.  Added a total of 96oz.  At 94° ambient, static low side was 110psi and high side 135psi.  Running pressure at high idle, max fan, not recirculating, was low 21psi, high 165psi. Vent temp was 59.4°. Pressures seem low and vent temp seems high, but I am already double the charge of the sticker.  Any insight would be helpful. Thanks

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a properly charged system will lower the air temp in the motorhome 20 degrees measured at center vent. I question the pressure gages. You have way to much freon in system.

Bob U 2000 Dip

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I would stick with the 52 oz.  If that is what it says.  There is no way to check the performance of the system unless you are moving the proper are across the condenser.  Try the 52oz. and get it out on the road under normal operating conditions.

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Matt, Is the condenser fan running when the coach is running? I doubt that this would be the problem though.  It is very probable that you have a failing compressor. The differential pressure looks weak. There is that possibility that there is air in the system. What was the gauge reading on the vacuum gauge and how long did you hold it for without the vacuum pump and did it hold? Just my two cents worth 🤗.

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First, never charge the high side, in fact don’t even open the valve. The gauge will read with the valve closed. Only charge the low side. When you are done the low side will read around 90 lbs, the high side anywhere between 230lbs to 250lbs, it should blow about 40 degrees below the outside temperature. If you cannot get the charge correct it’s because you put liquid  the high side. If you just let it sit for a day or two in the off position it might possibly balance itself out. Be patient. Remember; liquid only in the low side. I wish you the best. JM

Edited by Xracer
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MrAmbassador, 

The condenser fan is mounted on the side of the coach.  I swung it out so it could exhaust freely.  I also put a box fan in front of it.  The factory fan comes on when the dash switch is set to a/c. It was vacuumed for 1.75 hr at 30 inches.  It held this for 12 hours.  Static pressure says it is in the ballpark for charge, but the  low high side pressure made me question the compressor also.  Vent temps are 35° below ambient, better than nothing.  

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That’s a lot of R134 but it still sounds like you don’t have enough gas in the system. At 95° I would expect over 300 head pressure and the low side in the 40s or 50s, I’d have to look at the chart to be sure. Keep us posted. 

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Suction pressure will be low due to the long suction hose. 15 PSI isn't out of the ball park in my experience, but that high pressure is low for sure. What are you using to measure the charge, a bulk tank and a scale?

Also stupid question, but you turned the quick couplers clockwise to depress the service valve cores, right?

Edited by trailmug
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5 hours ago, MrAmbassador said:

Matt, Is the condenser fan running when the coach is running? I doubt that this would be the problem though.  It is very probable that you have a failing compressor. The differential pressure looks weak. There is that possibility that there is air in the system. What was the gauge reading on the vacuum gauge and how long did you hold it for without the vacuum pump and did it hold? Just my two cents worth 🤗.

Air in the system causes intermittent high side pressure spikes.. I'm with Bob, I doubt the gauges. Our coach was contaminated so badly when we bought it that it trashed a gauge set with sludge. (I think somebody put mineral oil-based UV dye in it.)

Also, the service valve cap is the primary seal.. the service valves are only there to give you time to get the cap back on.

Edited by trailmug
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Matt,

My 07 Diplomat dash A/C was acting similar to yours. I tried servicing it but never got it to perform any better than you. The high was too high and the low too low and discharge air was higher than I thought it should be. It cooled marginally at idle but at highway speeds the evaporator would freeze up. When I pulled over it would thaw and drain a lot of water.  I verified the condenser fan was working by wiring up a remote test light. I then suspected a contaminated expansion valve or drier so I replaced both, evacuated the system and charged it to specs. It works well now.

I cut apart the drier and found some rust inside. That led me to think improper servicing might have introduced moisture that led to  clogging the expansion valve or a restriction making it freeze up at highway speeds. 
Roy

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I had a situation once where the condenser fan was running slow and would stop. It would draw too much current that it tripped a 20 amp self setting circuit breaker.This also caused the compresser to stop as they are on the same circuit breaker. Replaced the fan which fixed the problem. Expansion valve being clogged can also cause your problem. If properly charged and everything is working right Then you should get a 20 degree drop at the center vent with a/c on max and blower on high.Get a temp gauge with a probe and measure at center vent, this is your ambient temp.Start engine,turn a/c on max, turn blower on high. Temp will drop 20 degrees in a few minutes.

Bob U  2000 Dip

Repairing a/c's since the old R12 days.

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