I need some help.

DIYer here. I have manifold gauges, vacuum pump, recovery pump and cylinder. I just replaced the evaporator, accumulator/drier, orifice tube on my unit. I had an evap leak and heater core issue. While I had the plenum out I rebuild the entire thing in hopes of not having to remove the dash again in the near future. The truck says it holds 1lb 11oz of refrigerant, I have refilled it with what should be the proper amount but I can not get my pressures and temps right. According to a r134a pressure chart @ 85deg I should have pressures in the range of 45-55 on the low side and 225-250 on the high side. I am more like around 35 on the low side and 175 on the high side. When I check my superheat and subcool temps I have the following. Subcool: gauge on high side reads 175 psi which equates to around 120 deg on the PT chart. My line temperature at the high pressure inlet is only around 93 deg. I have seen it up around 100 but not more than that. Superheat: low side pressure is reading around 35psi which equates to around 30 def on the chart/guage. My lines at my evaporator are running around 47deg, which puts m y subheat at 17. I did manage at some point to get my evap temps down to like 42 and the truck was cooling great sitting at idle, but when I drove around the block by the time I got back to the house I had 65 degree air coming out of the vents. I figured at that point, I may have overcharged it so I evacuated a little with my pump but no dice. The best I’ve been able to achieve are the numbers above with 50 degree air blowing out of the vents while idling in the yard and driving around the block. What do I need to check next? It seems to me my out put side of my compressor may not be doing what its supposed to be. From what I can tell my condenser is only dropping temps of lines, at the most 10 degrees from input to output. My condenser fan runs as it should. One thing I noted is my compressor never seems to shut off. Once the system has enough refrigerant in it to activate the clutch it runs as long as I have the ac on, no cycling at all. Is that correct? Thanks for any help you guys can offer.

 

i did fail to mention I added 2.5 ounces of Pag oil back to the system after the accumulator and evap change.

 

Looking at the numbers, I would say you are still undercharged.

How are you adding refrigerant to the system? If you are using the cans from the parts store, you can never empty those completely......

 

Yep that is what i'm using. I added it as follows. truck calls for 1lb 11oz which would be 27 oz. I added 2 oz for mainfold hose and 1 oz for each can which gave me 32oz. I added 2 cans and half or so of the other one. I can add more, but felt like i should have been pretty close on what i had charged it back with.

 

Pretty close, yeah. Trouble is, unless you have an actual pump sucking the stuff out of the can, and pumping it into the a/c system, the can will only empty to the point where pressures are equalized, and the more charge you have in the truck, the more you end up leaving in the next can you try to use. So, while you may thing you are putting in 12ozs per can, (assuming a 12 ounce can) that really isn't the case. Its more like 10 for the first one, probably 8 or 9 for the second..... etc.

 

thanks for the replies. this afternoon I hooked the gauges back up and I had around 40psi on the low side, around 55 degrees on line coming out of the evaporator, 200 on the high side with a 93 degree temp on the high side line. i added more refrigerant a little at the time and as I would add my low and high side pressures would climb along with the temp coming out of the evaporator. according to the ambient temp my low side pressure should have been around 55 and high side around 250. i got the low side up to 55 but the high side never got over about 230. when the low side got up to 55 my evaporator out line was reading like 65 degrees. high side line was around 96 to 100. i was seeing about a 10 degree temp drop differential between the input and output of the condenser.

 

So you added more refrigerant, and outlet temps (vents in the dash) went UP?

 

 

Ok your Dodge truck has a fixed metering device on the a/c. 35 psi on the low side gives you a saturation temp of 39.95 not 30. So you had 7.5 of superheat. Whit the fixed orifice the charge is critical. You need to charge using superheat... You might have been a little overcharged.

 

Four year old thread.......