Air condtioning problem NOT a tractor, but . . .

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.

moisture in the system that keeps freezing up and clogging with ice particles... maybe the new dehydrator will eventually remove it. or someother clog floating around.. have pulled out hair balls, lint and black tar balls, red sand.. dont know how they get into a system. sometimes the come in on the ends of charging hoses??

Hi JD,

Hey, walk away from it, then come back at it like it was a "fresh" job and like you've never laid eyes on it before.

Look at that high side pressure. Notice anything? Betcha somewhere along the line this ol' gal ate a compressor.

Your high side limit switch is shutting you down.

Either you have no air coming across the condenser or it is full of crap. At any rate, that pressure is WAY, WAY, WAYYYYY too high.

With an air temp of 70 degrees, you ought to be seeing a high side of between 150-170 lbs.

Just my two cents,

Allan

Hello Jdemaris,
The sysytem charged with the proper amount of refrigerant should have put you in the ball park.
It seems that its about 1/6 off at the compressor return temp. 12ounces of EXTRA, refreigerant made a difference.
The blending system may be at fault, heat to air ratio is about 3 to 1,btu's there is, that is why adding heat to the air will modulate the output temp. If the heat is overwelming the A/C, and the a/c is working fine, you should see a lot more of condensate coming out of the drain then normal. 12 ounces extra is way too much. What happens with the exta amount of refrigerant is that is gives you a bit more cooling power, but it also adds pressure to the system. When the low side pressure rises so does the high side. The output temp also goes up.
I would try this. Take the heater hose/s going in to the air box and close them shut. I use 2 big flat washers and a vise grip. This will tell you if the heat is on full blast. Remember with a 3 to 1 ratio, heat will win the battle. Hope this helps.
P.S. F350 full of fuel 7440 Lb.
Good Luck................... Guido.

I agree with Allen, your pressure is way too high. You have overcharged it. I suspect your blend door is not working all of the time. In my experience the front seal on the compresser is where it usually leaks. I usually only add 1 ounce of oil. Maybe you added too much oil. This is a question I would like to have answered myself. How do you know how much oil is left in the system and how much to add?

Hello rlp in CO,
There is no way to know how much oil is in new
Systems, add 1 to 2 oz max.
Thats why you only add a little at the time. When the system is open you empty the oil out and fill the compressor withthe proper amount. Old systems you could check with a dipstick, just like your car. Oil circulates throught the system, and too-much oil will effect cooling capacity. Its a lubricant not a refrigerant, so cooling capacity goes down.
Guido.

something is plugged up.whether it is the new expansion valve or the evaperator or condensor.did the instructions that came with the compressor say it was wet or dry.if it was wet then it has way to much oil.you should be running about 40psi on the low side and 150 on the hi side

I know it is not overcharged - I measured carefully. I also know the condensor is not plugged; it is brand new. As to oil capacity? I just put in a brand new compressor, drier, condensor, expansion valve, and all new lines. The only old part remaining is the evaporator and I flushed it. Even if I hadn't, the evaporator can't retain much oil. So, with the newly added 5 ounces of PAG oil, it's not going to be over-full.

I agree, that trying to guess at oil content is often difficult, but not in this case.

As to common leaks? When I lived further south, the compressor shaft-seal was the most common problem. Here in heavily salted New York? The condensors rot out something terrible from road salt. I've had two condensors rot out in my 98 Kia Sportage. Also had to replace the condensors in all our Subarus at least once. Same for all my GM trucks. In fact, on my 87 Suburban, I've replaced the condensor twice, and also gave up on the long aluminum lines to the rear AC. After they got rot-holes twice, I made 16 foot long rubber AC hoses to the rear. I used to think aluminum held up better then steel with road-salt. Boy was I wrong.

Funny thing is, my 1979 Datsun 280ZX has AC that still works great. Still has the original factory fill of R12. Same for my 1994 Ford F-250 diesel. But neither of those rigs ever get driven in the winter.

YOU MENTIONED THAT THE PREVIOUS OWNER ADDED FEON AND SEALANT. I HAVE SEEN THIS CAUSE SLUDGE IN THE LINES LIKE TAR.IT MAY NEED MORE FLUSHING OF THE EVAPORATER,OR,EVEN THE LINES MAY BE RESTICTED WITH THE "SEALER"/TAR/GUNK.YOUR ORIGIONAL PRESSURES WERE TOO HIGH. ALLAN MAY BE RIGHT ABOUT AIR FLOW THRU THE CONDENSER. SINCE IT BEGAN TO WORK BETTER,MAY BE A PROBLEM WITH ENGINE FAN ; VISCOUS FAN LOCKUP 1 TIME ,FREE WHEEL THE NEXT? ALSO DID YOU CHECK IT WITH CAB BLOWER ON HIGH? WAS VAN IN SHADE OR HOT SUN WHEN YOU WERE TESTING IT? IT TAKES LONGER TO COOL DOWN A HOT CAB THAN A COOL ONE. AS THE CAB COOLS DOWN BOTH PRESSURES WILL DROP SOME AS HEAT IS REMOVED.BUT,IF IT IS WORKING NOW,LEAVE IT BE AND TEST DRIVE IT FOR A WHILE , MAYBE IT WILL STAY OK. GOOD LUCK,MARK

For what it is worth. The tech that set up my heat pump at homesaid that you cannot get a full charge when the outside temp is too low. he charged up my system til pressures were right. outside air was 65. when temps got up to 85 outside, he came back and charged system up to specs and everything has been great since. Something to look at. good luck. If lines are freezing then you have too much gas.

Sounds like to me the thermal expansion valve was stuck open too far. When the valve is too far open for the ambient air temp, the pressures will be elevated on both sides of the system. With the valve stuck in the closed position, the pressures will be low due to the refrigerant being mostly trapped in the condenser.

(quoted from post at 09:58:04 05/23/10) Sounds like to me the thermal expansion valve was stuck open too far. When the valve is too far open for the ambient air temp, the pressures will be elevated on both sides of the system. With the valve stuck in the closed position, the pressures will be low due to the refrigerant being mostly trapped in the condenser.

Click to expand...

I agree with you Brian, then there is always the 'but..."

He said, "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."

Yes, it is not impossible to have a new bad part, but odds are against it. Not that it isn't worth checking though.

He may have backed away, as it is only us 'others' posting now...no JDemaris in last 26 hours? But he has been active on several other forums. Sometimes good to step away & let it simmer awhile.

I'm just waiting to see how long it keeps working. We're not using the van now, but I have been starting it each day and checking since I posted. Still working well. So, at this point - I'm going to assume that maybe the problem was with the oil not being disperesed evenly throughout the system? The entire initial 5 ounce oil charge was in the new compressor when I started. All else was dry. After charging, and the AC not working, and pressures surging - I know the surge wasn't the compressor cycling (it was running steady).

Basically, it didn't work and I gave up went into the house. That was after fooling with it for maybe half an hour after the charging was done. Next day, it worked fine and is still working fine. I've never had that happen before, and it seems the first half hour should of been ample time for the oil to circulate. So, I don't pretent to know what happened, but it IS working fine. No surging, cools fast, etc.