roughstock

I just had ac serviced, everything worked fine except compressor won't kick off. The pressure get to 250+ hi side. Seems high.
I changed out hi pressure and no change.
Other relatively new parts include drier, o-tube, condensor, compressor.
It cools great, hi side just seems too hi.
Any help is appreciated.
I'll trouble shoot the wires to hi pres. later today.

1-2-3

250 isn't too high. It will change as outside temps change. On a really hot day it'll be 300. Your system will hold 600 easy. On an average day, 250 on the high with a properly working system will put the low about 35 which would be about right.

nickg

I've gone thru a couple of switches that seem to "stick" on causing the ac system to ice up

roughstock

I'll do some more checking, but it was 75 yesterday and it still wouldnt kick out. I just dont want to blow out any seals from too much pressure. Just got AC charged and ready for summer. Its suppposed to be in the 80s+ thru the weekend.

Stamey

What normally kicks out the compressor is the low side switch, on the accumulator. When the pressure drops to a certain point it kicks the compressor out to keep it from icing up on the low side, and too much pressure on the high side.
I would not worry about the high side pressure until I saw it exceeding 350 psi. Then you might want to look for a blockage in the system.


Chris

bob4x4

here you go

HIGH PRESSURE RELIEF VALVE
The high pressure relief valve is located on the compressor manifold. The valve is used to prevent excessive system pressure. The valve vents the system when a pressure of 3445 to 4135 kPa (500 to 600 psi) and above, is reached. This prevents damage to the compressor and other system components due to condenser air flow being restricted or an overcharge of refrigerant. The valve closes with a minimum pressure of 2756 kPa (400 psi)

The high pressure relief valve vents only enough refrigerant to reduce system pressure, then re-seats itself. The majority of the refrigerant is conserved in the system. If the valve vents refrigerant, it does not mean the valve is faulty. The valve is only serviced as part of the compressor assembly, and must not be removed or otherwise disturbed.

HIGH PRESSURE CUT-OFF SWITCH
The high pressure cut-off switch is located on the discharge line near the compressor. This switch is connected in series between the low pressure clutch cycling switch and the Powertrain Control Module (PCM) This switch prevents compressor operation when the discharge line pressure approaches high levels.

When the discharge line pressure rises above 3100 to 3375 kPa (450 to 490 psi) the switch contacts open and interrupt the A/C request signal circuit to the PCM. The PCM responds by de-energizing the compressor clutch relay, which will cause the compressor clutch to disengage. The switch will close again when the pressure drops to 1860 to 2275 kPa (270 to 330 psi)

The high pressure cut-off switch is a factory-calibrated unit. The switch cannot be adjusted or repaired and, if faulty or damaged, it must be replaced.

roughstock

Thanks. Now I have to figure out why it wont cool at idle. My AC guy says the Oreilly's Brand Fan clutch is not moving enough air.
Might go to OEM clutch or mybe dual electric and no belt driven fan.

roughstock

FYI,
It was 80 today and I put gauges on the AC and it was 400+ on high side, so I shut it off before it got too high, but I guess that isnt too high.

nickg

if condensor is externally plugged (or fan not working) could give same symptoms, have you looked inbetween your rad and your intercooler to make sure its not dirty, usually they are plugged solid with dirty oil,(from puke bottle) lack of air flow will not allow the fan to enguage, causing overheat issues and poor ac performance

roughstock

NickG,
Thanks for the input. I checked that. we have those problems at work with the construction tractors working in the dirt all the time.
The truck runs cool, has a OEM cummins thermostat.
The fan clutch is what I am thinking is part of the problem. it is an aftermarket from O'reilly Auto. It is keeping the truck cool(not too hard to do), but its not locking up enough to keep AC going. Im going to junk yard on Tuesday to pull an electric cooling fan from some thing and put it in front of condensor and wire it into the AC. But first I'll prob experiment with a box fan
I'll prob just try a box fan, just setting in front of condenser, first before I actually start fabing the elect. fan thing
Or maybe I could just go to dodge and get OEM fan clutch.
Wonder how may hundreds of dollars that is?

roughstock

I put a big box fan in front of condensor. it helped quit a bit at idle, so I guess im not moving enough air.
Also, the line that has the Orifice tube is super cold until it gets to the O-tube, then it is scorching hot after that point. is that normal?

Stamey

Yep, normal.

Chris

roughstock

OK, i thought so.
Ive been noticing that the AC doesnt get real cold until the truck temp heats up, which makes be believe that the Fan isnt moving enough air, then when the truck gets hot, it engages and moves more air and then AC is better.
SO,
Do i get a new OEM/cummins fan clutch,
or,
Get an electric cooling fan(wired in to AC) and run it in addition to Belt driven fan,
or
ditch the belt fan and go with two electric fans?

Stamey

Step back a minute. What is "real cold"? Get a thermometer into those vents. Most AC systems in vehicles work in the fashion that riding down the road gives you cooler air than sitting still, because of the additional air coming through the condenser. I'm trying to figure out if your expectations are too high now. What is the temp coming out of the vents sitting still, at idle, on Max AC, with fan on high? Now, what is it when riding down the road at 55mph? You can do this test cold then again when the engine is warm to see what difference there is.
Whatever you got from O'Reilly's should be functionally equivalent to OEM, though it may not be of the same quality. If it isn't, you should be getting a different one. It appears that they carry 2 different brands, Murray and Hayden. Which do you have?


Chris

roughstock

OK, I see your point. Ill put a thermometer in it. But just me sitting there i can tell it is Very cold going down the road and at idle it is almost warm. I used to be able to sit and idle all day and it would keep up.