In a nut shell, I need help to know I am dealing with the low pressure port on my AC. But first, let me tell you what I have and what is going on.

1995 Dodge Ram 3500/12V Cummins/47RH

Last year, my AC was working, but seemed not as well as it was. End of season, so I just left it for this season. This season, now AC not cooling at all. I assumed it just needed a re-charge. Today, I went in to connect my gauges. I found two ports that I assume are the low and high sides. One is at the front passenger corner of the engine bay, behind the headlight. The other is also on the passenger side, but lower near the engine block (front). As I started to connect my QD fittings from my gauges, I noticed both those ports are the large size and only connect to the high pressure fitting from my gauges. I do not seem to have the smaller port for the low pressure QD. Now I am confused as to which is which? I can connect the high pressure QD to either of these ports. But I can not seem to connect both gauges at the same time since I only have one of each QD (small & large). Which one of these are the low pressure service port? Or if neither, where can I find the smaller port for the low pressure side? Any help and/or pictures would be very helpful. Thanks in advance.

As a side note, checking these ports seem to show the same pressure (around 90-100 psi). The compressor clutch is cycling, but on/off ever few seconds. If that is the high side, it is low of course, if it is the low side, it is high. So, I am not so sure I am even at the low side at all. I am confused. Thanks again.

 

Compressor cycling quickly is generally a sign of low charge. You can get a service manual for your truck from here. Should show which port is which.

I suspect you have a slow leak somewhere.

 

I actually have that manual. But it does not show the ports, only tells you to connect to them.

 

Should be a diagram that shows them somewhere......

I could find the high pressure port, it's supposedly on the block the lines go to on the compressor. I suspect your system might have originally been R12?? And just has the adapters on the pressure test port??

 

that is what I originally thought (originally R12), but in the manual, it says that 1995 has R134a system. Everything that I see shows that it should be the one at the right (passenger side) front corner of the engine bay (behind the headlight). It does have a port there, but it has the larger QD port (like the high pressure QD). That port should be the smaller QD fitting. This is what has me confused as hell as to which one, and if it is the one it is supposed to be, WHY would it have the larger QD fitting? I am at a loss, this is why I would love someone with a 95 show a picture of theirs, and if they have the large or small QD fitting there.

 

Here is the port that I would believe is the low pressure/suction service port, But, it has a large quick disconnect fitting on it. (I can connect the high pressure QD to it, but not the low pressure QD).

 

Is there a fitting on the receiver/dryer?? Some pics show it, others don't, still others show that's the port for the low pressure switch.....

 

Something ain't right. The FSM says "The low pressure hose (BLUE with BLACK STRIP) attaches to the suction service port. This port is located at the right front of the engine compartment in the condenser-to-evaporator line" but the condenser is definitely on the high pressure side. On my 2001 the port in the picture is the high pressure side, and the low pressure port is near the accumulator. Some googling shows that the 12 valves might have two high pressure ports, one before and one after the condenser which might be causing the confusion. Trace all the A/C lines the port must be hiding somewhere...

 

Thanks Dertruck. That is what is confusing me. I looked back by the accumulator and did not see a port, but will look again and try and follow the lines. Hopefully, one will turn up. I just might have two high pressure lines, because of the size of the fitting (which is what has me confused also), and the fact that the pressures in each of them was about the same at 80-100 lbs, which is low for the high side. I just need to find another port along the line somewhere hiding from me.