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adminvtt
Dodge Dakota
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8/26/2003
08:30:12
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 Subject: AC not blowing cold enough
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R-134a charge is right on the money at suggested lbs. of pressure. Ac compressor clutch works fine kicking the compressor both on and off in cycles like it should. R-134a dye added no leak detected. Evap does drip allot of water but as far as I can tell it is not iced up. But air coming out the vents is just not cold at least not enough to make you comfortable in 89 degree weather. Low pressure side is cool to the touch but not cold, high pressure side is hot like it should be. Sounds to me like possible clog causing freon not to move through the system but I would like another opinion as getting it flushed cost money and I'm a poor boy.
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peedee
Dodge Dakota
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8/26/2003
14:34:50
|  RE: AC not blowing cold enough
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If the pressures are good, there can't be a restriction. A restriction would cause high pressure on one side and low on the other. The problem with most ac units not providing cold enough air is either an externally dirty evap, or condenser, but again, the pressures would be off. Pressure / temperature relationship is the key to refrigeration, as you probably know.
The most likely culprit is the humidity of late all over the country. The reason; the specific heat - amount of btu required to heat, or btu absorbtion capability - of air is .25, while the specific heat of water is 1.0 . So, to heat one lb of water one degree requires one btu, and to absorb the same amount of heat, one btu of potential is required. To heat / absorb one degree in air, requires .25 btu. Best thing is to run the ac on normal to get outside air which is usually cooler than inside when first started, then switch to max for recirculation of inside air which may be still warmer than the outside, but much drier, and therefore much less of a load on the system. Of course the rpm means a lot too. if a compressor is rated at 5hp of cooling that hp is only achieved at about 1/2 to 3/4 rpm. Plus the fact that this time of year the sun is at a much steeper angle and heats surfaces in the vehicle much more thoroughly. But, the humidity is the BIG factor, usually. Take it for a ride on the highway to have constantly higher rpm, say at least 1500 - 2000 and see if it makes the diff. If so then the system is probably working the best any can. Or move to a less humid place...... lol
Hope that helps, and i hope you live in a humid area of the country, or my theory is blown to hell, and in that case then I was forced to type all of this.....
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PeeDee
Dodge Dakota
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8/26/2003
14:40:13
| RE: AC not blowing cold enough
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BTW, cooling requires more potential than heating in btu because the process of cooling has to account for friction whether mechanical or molecular - superheat.
Also: most cooling sytems that use gas for a refrigerant are designed to have 95 degree air over the condenser at 75 - 80% humidity. Any more humidity = high load on the system. But you would have had a high condenser side pressure if that were the case, so again it is most likely the humidity inside the compartment and the heat the inside surfaces are emitting.
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adminvtt
Dodge Dakota
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8/26/2003
14:59:54
| RE: AC not blowing cold enough
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Thanks Peedee. I gave that some thought and I was aware but just wanted to make absolutely sure that pressure good means no restriction on freon flow. I also understand that R-134A usually only reduces temp. to 20 degrees below outside ambient temp. But my system is definitely not doing this, humidity I did give some thought to that. Driving on highway with engine RPM at 1500-2000 makes a slight difference but Temp still not dropping low enough. At a minimum it should be cooling 20 degrees below outside air and I'm firm on this there must be something, what do you know about R-134a does it break down in composition? Could it be old and need to be flushed and replaced with new?
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TexasTodd
Dodge Dakota
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8/26/2003
16:00:53
| RE: AC not blowing cold enough
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Want to turbo charge it? Put a ball stop valve in the water inlet to the heater. It works!
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PeeDee
Dodge Dakota
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8/26/2003
19:48:32
| RE: AC not blowing cold enough
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It won't break down w/o some ather failure such as an electical component burning, moisture or something else to contaminate. At a standing temp - inside, 70 - 75, your low side pressure should be around 70 - 75, 134 is works out close in #'s. At operating temps inside at 70 - 75, your evap should be around mid to high 40's. but up to 55 is not bad. The pressure is the average of the low side from the cap tube- or expansion valve - to the compressor. to get a true temp, you would have to stick a therm in between the fins of the evap. Then take the temp of the line leaving the evap to the compressor. You should have about 10 degree lower temp leaving - subcool. The high side is a bit more tricky. ambient has so much to do with it. but the industry standard is @ 95 degrees air through the condenser coil. tought to state a pressure here, with superheat and all. but the compressor is doing light duty when you are testing in the driveway at low rpm, and reving is not good, because you would have to for too long to let the system stabilize. If the pressures remain constant and dont climb or drop too much too sudden, you are good. As the low drops the high should too, it is doing less work. But it should not drop too far from what i stated. If you get a coil temp lower than at 70 compartment, you may be low on charge. the systems don't take much charge, so a small amt low is big.Sorry I can't help more, if I had hands on then it would be easier. I usually work on industrial equipment 300 ton or larger and cold absorbtion machines so I do a lot of diagnosing at work.How does it perform at night, w/o the sun beating down? that should let yo know how it is. Usually a slightly low charge will start to ice the coil as the compartment temp lowers at night because there isn't too much load.
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adminvtt
Dodge Dakota
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8/27/2003
07:12:21
| RE: AC not blowing cold enough
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Thanks TexasTodd but I just want it to run like it did when I bought it. And PeeDee thanks your info is very accurate. I put a tune up bottle in the system and it put it right on the pressure line between full and whoa! back up a little. It did get colder I also bought another pressure gauge just to make sure and they both read the same. I drove to work this morning and got to the base at 0455 and it was very cold in the cab of my truck but I'm sure by this afternoon it will be warm. Outside air is 79 and in the cab its 48 that was the difference I got this morning.
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adminvtt
Dodge Dakota
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8/27/2003
08:20:34
| RE: AC not blowing cold enough
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one more question there PeeDee. You seem to be very knowledgable about Dakotas, What Store bought brand and weight tranny fluid can you use with Dakotas. I have I believe the NX1500, manual 3.55 gear ratio 98 model for a 3.9L V-6. I haven't found a manuel that states the specifics they all refer to a part number for a dodge parts and I looked up mopar parts and I still didn't find anything under the part number. I just want to run into Autozone or Advanced auto and grab some 80W or 90W and change it myself. But some manufacturers require a specific additive like Ford or the tranny foams and dies. Also if you know what to use for the rear differential I sure would appreciate it.
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