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01:26:44 - 12/20/2024
General Dakota Board
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mpbronso
Dodge Dakota
JOIN HERE
6/29/2006
15:00:41
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 Subject: Weird--AC Pressure Buildup?
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2000 CC 4.7L
AC is hit and miss. I’ve read a lot about the problem with the evaporator drain tube getting plugged, but I am confident that is not my problem as the tube seems to be clear (I can stick my finger in up to one knuckle) and water drizzles out of there when the AC is running well.
After about 20 mins. of running it will stop blowing cold air. When it does this the compressor will not engage, despite the AC control being set to max. Also, when it does this pressure in the system is about 75-100psi, so obviously the compressor shuts off because of the high pressure (On the other hand, pressure after about 5 mins. of running is in normal range).
Sometimes after a prolonged period of the compressor not turning, it will come back but only for really quick spurts (maybe 10 seconds at a time), but not enough to keep the air cool.
Here are some other symptoms I’ve noticed:
--The accumulator, in summers past, used to collect a lot of condensation and even freeze it, coating itself with ice. The accumulator does not get wet, even when the AC is working well.
--The line from the evaporator to the condenser collects a lot of condensation, but the line from the accumulator to the evaporator collects none. I understand this second line is actually supposed to be colder than the first…?
--At times, usually within a few minutes of starting the truck, I hear running water from the passenger side. This is a mystery to me as I am confident the evaporator drain tube is clear and drains well.
Anyway, I know the compressor engages, the fuse and relay are good, the high pressure switch obviously works…
What gives? Why is it building up so much pressure, what else can I check or try to fix?
Thx
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BigEd
GenIII
6/30/2006
07:14:32
|  RE: Weird--AC Pressure Buildup?
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Message:
High pressure cut out is in the 300 psi range on the HIGH side. if your suction pressure is 75-100 on the low side, that would be normal with the compressor off. (pressures equalize when the compressor is off)
The suction line (evap to the compressor should be cold to the touch, even sweating)
From what you've said, you are short on freon. You most likely have a small leak.
The LOW pressure switch most likely cut out the compressor when the temp in the truck dropped and the pressure on the LOW side dropped below setpoint. (about 15 psi or so)
As for the water on the pass. side floor. I had this problem also, it was my drain tube on the fire wall behind a heat shield. It was clear but it seemed that turbulant air in the engine compartment would "push" the condensate back and leak inside the truck instead of draining down the outside firewall when moving on the highway. I installed a 90 deg street elbow (1/2 inch)and this allowed the cond. to drian downward.
So, did you actually have a set of refrigeration guages on the system???? If so, you should have about 35 psi on the suction side when running and the compressor engaged. Run up the RPM to about 2500, pressure will drop, if it goes below the suction pressure switches setpoint, it will cut out your compressor.
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mpbronso
Dodge Dakota
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6/30/2006
09:48:29
| RE: Weird--AC Pressure Buildup?
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Message:
that makes sense about the pressure equalizing with the compressor off--thank you. but why will it stay off for 20-30 mins at a time?
eh, I just had a cheap-o Wal-Mart gauge on the low side. i've tried putting more 134a in it. sometimes it seems like it's not taking any, or it will just take a quick spurt and then it seems like the pressure is too high for it to accept anymore...
as far as a leak, i've meticulously checked the lines and don't see any signs of any oil, or excessive wear or weathering.
i don't know...
i have a 13 month old who i take care of most days, it kills me to have to drive her around in the Texas heat without any AC...
could it be that the relay is faulty, but still works enough for the compressor to engage when the engine is cold?
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Tfw
Dodge Dakota
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6/30/2006
13:16:59
| RE: Weird--AC Pressure Buildup?
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The line from the condensor to the evaporator should be hot with the compressor running. If it's cold there's a restriction in the line or condensor. I too had an intermittent problem with my 98, turned out to be the compressor relay, so I just swapped with the horn relay as I seldom use the horn.
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BigEd
GenIII
7/01/2006
09:45:35
| RE: Weird--AC Pressure Buildup?
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Message:
Could be a restriction but I believe your short of refrigerant. If your low enough the refrigerant will boil off BEFORE the evap. (In the line from the condenser to the evap.) Causing it to be cold. You really need to put on high and low side guages to see what the system is doing on either side of the compressor. If there is a restriction, you'll know for sure if your high side goes way up and the high side safety stops your compressor. But if you say it runs for 20 min or so, I say no restriction cause if there were, it would stop almost immediatly.
You really need to have the system evacuated, put on a vacuum pump to get any moister/noncondensibles out of the system, leak checked and then recharged with the proper amount of refrigerant.
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mpbronso
Dodge Dakota
JOIN HERE
7/07/2006
13:18:09
| RE: Weird--AC Pressure Buildup?
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UPDATE--
I think I had a crappy guage and R134a can/system thing. I bought another one yesterday and it worked much better. I also was making the mistake of not tripping the high pressure switch so that the compressor would stay on while trying to charge the system.
So, I did all that yesterday and the system took a good deal of 134a...with strange results. The line running from the condensor to the evaporator (beneath the accumulator) actually froze up, but the line from the evaporator to the accumulator never got cold. I let the system run for a minute, but it never blew cold air. Then when I shut off the engine, I heard air hissing out, and from all I could tell it was coming out of the actual low pressure side access port/valve. Putting the plastic cap back on seemed to stop the hissing...
Is it possible my leak is at the port?
My other thoughts are possible a bad evaporator or a blocked line near or at the evaporator?
Sorry to keep this post going, I'm just very reluctant to give the dealership any chance at my business, even for a diagnosis...
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BigEd
GenIII
7/07/2006
14:31:59
| RE: Weird--AC Pressure Buildup?
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Message:
Without proper gauges, you really don't know what the system is doing. You need to to take high AND low pressure readings with the compressor running. Sounds like you've found the leak. If you put the recommended amount of refrigerant into it, you should be ok. You won't know that unless you evacuate whats in there now, have it put on a vacuum pump to remove all air and other noncondensibles, then weigh in the right charge. There should be a sticker in your engine compartment with the proper amount. You can get by with pressure reading but weight is the best. If you have alot of moister in your system, it can freeze also and cause a temporary blockage. I think your just low on refrigerant and its leaking out too fast to really make it work right.
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shatto
Dodge Dakota
JOIN HERE
7/09/2006
18:41:09
| RE: Weird--AC Pressure Buildup?
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Message:
Big Ed mentioned a small leak.
My mechanic found my small leak under the cap on the tube along the fender. The rubber valve stopped sealing. New unit on order.
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