Model: Grand Voyager
Engine Size: 3.3L
Refrigerant Type: r134a
Quick question to run by y'all. Not sure if any of this is indicative of a problem or not.
I've been noticing lower AC performance this past week, and decided to check into it. System seemed rather slow to cool down. Standard FSM charge procedure (other than by weight if starting from a vacuum) is by subcooling - it apparently comes out to about 25ÃÂ°F subcooling.
Hooked up the gauge set and the high side would not work - it would snap on to the fitting, but there was no rise on the gauge. Hose end coupling is designed to automatically depress the valve in the service port. Low side worked fine. High side pressure rose enough to turn on the fans though.
Ambient was about 85ÃÂ°F, low side was running 18-22, vent temp was around 53ÃÂ°F. Clutch was cycling frequently due to evap temp sensor. Verified evap temp sensor was correct by inserting an electronic meat thermometer into the evap next to the sensor - temp would drop to about 34ÃÂ°F before the clutch would disengage.
Decided (against good wisdom probably, with no high side reading) to add a few oz of 134a and see if the problem improved. Added about 4-5oz and was able to get vent temp down to 48ÃÂ°F and low side up to 20-25. Clutch continued to cycle frequently.
Got an idea to check the superheat tonight, ambient 70-75ÃÂ°F, hooked up low side and thermistor (at low side port), and superheat was ranging around 20-25ÃÂ°F. Vent temp came down to 39ÃÂ°F, and the clutch cycled a few times but not frequently.
Vehicle is very high mileage - 274K miles. Went through the AC system 7 years ago (at about 98K miles), replacing txv and drier and flushing the system, out of some concerns about a repair done by a shop during the van's previous ownership. The only AC work done since then is to occasionally top off the charge (using the subcooling method) by adding a couple oz.
All readings taken with controls on recirc and blower on high or near high.
Anything here look out of the ordinary?
The evaporator is 34 but the vents are 53 -- this is reheating from the heater core not a refrigeration problem.
Once the compressor is cycling on evaporator temperature you can't make it any colder by improving refrigeration performance under the hood, it would just cycle off longer.
Edited: Tue August 19, 2014 at 7:41 AM by mk378
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