2nd Gen Non-Engine/Transmission Another ac problem/question

[esamuelson]

I have looked through the previous post for ac problems but am not seeing the problem that I am having. I do not have a leak or if so a very slow leak. The system holds good pressure, but just is not blowing cold air (65 degrees F. ). Outside air temp was at 88, low pressure was at 55. I have found that the lower the low pressure side is the colder the air at the vents. The problem is when I set the pressure at around 40 psi at idle, when you drive the truck, the compressor cycles because I believe the low pressure is drops below 25 psi. I tested the low pressure switch and when pressure drops below about 23 or so the compressor kicks out. It seems I have to have my low pressure higher at colder temps to keep the compressor from disengaging but than at higher temps the low pressure is high and my vent temps are high. I removed the blower fan and looked up in and didn't see any debri. My drain is clear and working. Are these systems that inefficient? My father in laws Dakota has 39 degree temps at the vents :--)

 

[Steve Graham]

What is your high side reading?

Steve

 

[ToolManTimTaylor]

Sounds like uncompressables (I. E Air , moisture , left over nitro from p-testing) in the system or the accumulator is very dirty.

 

[esamuelson]

I had taken high pressure readings before the above test and they were within factory specs but in the process I found a leak at the high pressure fitting. I resolved this problem but did not borrow the full manifold gauge set again to do the above tests and tuning, I had just a single gauge. I can retest high pressure readings if this would be helpful. How would I tell if the accumulator is dirty or do you just replace it? To fix the moisture in the system or nitro ( which I didn't use) you would drain system and vacuum correct? Could there be to much oil in the system? How would you know?

Thanks for the help.

 

[ToolManTimTaylor]

The accumulator contains desiccant to remove moisture. Once saturated they can become very ineficcient and can allow acids to build up in the system that form when moisture is present. The reason for evacuation or drawing a system into a total vacuum for at least 30 minutes is to remove air and moisture from the A/C system after being serviced.



In instances where the system was open for a short period of time, or if contaminents like air are introduced into the system, this will ensure that the refrigerant is boiled off and the proper charge is made with the best results. Off the shelf charge cans from autozone introduce small ammounts of air into the system as the hoses are not purged prior to hookup. The whole system has I believe 2. 8 Oz of oil and an accumulator is something like 25 bucks from Rockauto. I replaced mine back when the evap and heater coil was replaced up at Massdiesel. I figured it was cheap and easy insurance for the completion of a major undertaking.

 

[Neal Cassady]

On my truck the low pressure switch cuts out at around 23 psi. I add refrigerant until I get around 34 psi at idle. Vent temp should be around evaporator temp plus approx. 10 degrees. If you overcharge the system a little bit you will have higher vent temps at low speed/idle but the compressor won't cycle as much on the highway. When you are moving down the road you get quite a bit of air across the condensor and that will pull the high side down a bit which will allow the low side to drop as well.



Vent temps should be between 38 and 42 degrees at temps around 88 with moderate humidity. Check to see if you blend door is operating properly. I don't have my gauges handy but with R134 temp is about 4 degrees above pressure in the 30/40 degree temp range.



Neal

 

[Reb.B]

possable causes could be a plugged suction line accumulator (ie. a/c dryer), plugged orface tube, or the valves in the compressor are worn. Also, does it work well when driving down the hiway or is it always warm. If its bad just around town, then the fan clutch could be bad. It fairly reasonable to change orface tube ($6) and the dryer. If you can get an old r12 can, you can save the old freon. Just hook up the can to the low side and put the can in a freezing container or full of ice. Its best to freeze the tank over night.

 

[esamuelson]

I have no problem changing the drier/acumulator. The orifice tube, I thought was in the middle of the liquid line and is non serviceable? I thought you had to change the whole line? The liquid line is cool on one side of the orifice tube and hot on the other, the fsm says that means the tube is ok? Should the compressor cycle while you are driving or be on all the time? The higher I have the low pressure the better it cools at highway speeds but still only about 50 degrees, but than the low speed/idle is higher temps yet. How do you test the fan clutch? I wish I had an electric fan or a switchable fan like the Kenworth I drive, you can run the fan at idle and chill the interior down quick.

Thanks for all the help so far!