Posted by jdemaris on May 21, 2010 at 06:43:20 from (67.142.130.23):
Yes, this is on a Dodge van and not a tractor. But the subject is more about fixing AC. Since some tractors also have it, maybe this isn't so off-topic.
Main thing is, after all my attempts to fix, this thing did not work. Then after leaving it parked in my shop for half a day, it "magically" began to work fine. Being mechanically minded, I have trouble with stuff that starts to work - all on its own. So, I'm seeking explanation.
This is kind of a long post, but I don't know a good way of making it shorter and still properly describe the problem. If there are any true AC or HVAC experts out there, I'd like some input.
My main concern here is - when something works or doesn't work - knowing what is really going on.
I've been an tractor and diesel mechanic for most of my life, but am NOT an AC technician. I usually know enough to get by and fix my own rigs - until now. This van is really starting to get to me.
I bought the van 3-4 years ago. 1998 Dodge Grand Caravan AWD, 3.8 engine and convoluted electronic HVAC controls. Front air only, no rear AC. As I recall, the previous owner was constantly adding refrigerant and sealant to make it work, but it would leak out in a few weeks.
I checked the obvious. Pulled a vacuum on it, and it held fine for days. I charged it with dye, it leaked out slowly and I still couldn't find the small but persistent leak. So, some sort of leak under pressure that does not seem to bother with a vacuum on it. More of a concern was, and is, I could not get good cold air out of it when it IS charged to factory specs of 34 ounces. If I add an extra 12 ounce can, it works better. That has me a bit stumped.
Well, never had a summer yet when the AC worked. This spring, I tried to fix again. I flushed it all out. I replaced all the rubber hoses, installed a new drier, compressor, condensor, and expansion valve - along with all o-rings. Pulled a vacuum on it and no leaks show. Held steady for three days while parked in my shop. Added 5 ounces of PAG 46 oil as the system calls for. Added 34 ounces of refrigerant. Nothing has changed except it seems the slow leak is fixed. With the factory recommened fill, no cold air. With an air temp in the shop of 70F, the low side is 35 - 45 PSI, and the high side is 250-275 PSI. Both sweep from the low reading to the high reading around every 4-6 seconds. I tried to check metal line temps but my thermocouple/temp gauge is not giving perfect readings. I do know this. The cool line near the compressor shows as 64 degrees F, using my suspect temp gauge. I used that same gauge on my Kia and Tracker (both AC systems work fine in them). Same line in them reads 50 - 54 degrees F on my temp gauge. So, at least I know the line on my Dodge is 10 degrees warmer then on the two rigs with good AC. I tried to check the hot line by the switch near the firewall. Best I can tell, when pressure is 250 PSI, the line temp is around 95 degrees F (but I don't trust the reading). It feels hot to the touch, but does not burn my hand.
At this point, I'm a little stumped. If the cold line was a bit colder, I'd suspect maybe something not right in the convoluted blending doors and HVAC controls? I'm also wondering why in my previous attempt, over filling with 12 extra ounces made an improvement?
Update. Now I'm even more confused. After working all yesterday morning on van, I gave up on it for awhile.
Last night, I went back to the shop. I decided that once again, I'd overcharge and see if it made any difference. But first, as a sign of my mental illness, I decided to try it again as-is and see if magically, anything had changed. It had!
I started the engine, turned the AC on, and it all worked great! Metal low line on the compressor immediatedly cooled to 48 degrees F. 50 F came out of all the air ducts. Low side pressure was a steady 28 PSI and high side a steady 240 PSI. No more pulstating every 4-5 seconds. So, at least now I know that this thing is capable of making cold air with only the OEM spec charge of 34 ounces. But . . . what the heck could of possible changed just by letting the van sit in the shop for half a day? It was still around 65 degrees F air temp in my shop last night, so no big change there.
Anybody got any ideas why this thing would not work when I first charged it, but hours later worked great? And why at first, low and high pressure readings would pulsate every 4-5 five seconds. Low was swinging back and forth 35 to 45 PSI. High had been swinging back and forth 250 to 275 PSI. And low line temp at compressor was only 64 F degrees.
Now (last night) after sitting, got steady hi and low PSI readings and same low line at compressor at 48 F degrees. Can this maybe have something to do with a computer "reboot" of some sort, or maybe the 5 ounces of oil that was originally just in the compressor had to get dispersed and circulate?
It it keeps working, that's great. But, I'm wondering if next time I go to use it, it might revert back to the "not working" mode. We drive this van through Canada and on to Michigan a couple of times every summer. Canada always seems to be hot and it would be nice to at least once, have the AC working.
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