Ac gurus need a quick answer

[BrianX128]

I guess since it's a 134a switch and am r12 compressor I cant expect perfection. I wonder if there is a vbelt compressor for our trucks that was ever r134a..

After I added a little more coolant it now runs constant at idle but will cycle at rpms after a minute and a half.

Also if I jump it to force it on at rpms what's the worst that could happen? Just frost the condenser over or could it build too much pressure high side and hurt something

 

[riphip]

Did you add gas until the eye was clear?

 

[BrianX128]

At idle yeah. I'm gonna have a helper rev it to 1500 and see what it's doing. It's got about 40 oz in it I'd say.

Edit

It stays clear at all rpms but revved up to 1500 or 1800 the low side is only at 15psi and so the switch throws and it cycles but at idle at 700 to 900 it will stay at 25psi and run all day

 

[BrianX128]

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Not to double post but we now think the compressor clutch on the old compressor is slipping. Were gonna try and make a small bracket to put this new 134a compressor on with no working welder..

 

[gnathv]

Do your instructions say how many ounces of 134 it should take.
My factory system is 38 oz. you may still be low. You can use a digital thermometer and check the inlet temp and outlet temp of your evaporator. Are you able to measure your high side pressure? If your clutch is slipping may be high.

 

[gnathv]

Is your drier in the right way? Should have an arrow for flow.
15 to 25 psi is starving your evaporator I believe. Knowing high side pressure would give needed information

 

[BrianX128]

Doesnt have a high side port in the kit. Drier is right according to directions.

 

[raydav]

The switch on the dryer is a low pressure switch. Monitor the output side of the switch and I believe you will see it correlate with the compressor clutch engagement. With a low charge, the switch will close when the compressor in not engaged, that will allow the compressor to engage, and when the compressor engages it will pull the pressure down to where the switch opens, and the compressor will disengage, and repeat.

I charge the low side to 30# at idle.

I think a system should have a high side port.

Compressor cycling to avoid evaporator freeze is controlled by a temp sensor in the evaporator. If there is no wire going to the evaporator, then there is no temp sensor. I have assembled a system without a temp switch, and the evaporator froze, and the ice blocked enough of the air flow that cabin temp went up. Temp switches are available.

As an aside, I work on old systems that were originally R12. For at least a decade I have been using Envirosafe. It is not near as expensive as R12 but still significant. I just bought two 30# cylinders. But for several years I have suspected that it was just propane, or "barbecue gas". So I finally tried that. Works great.

 

[typ4]

I would quit screwing with it, your cycle times are about right, before changing the compressor, put a kicker relay on the clutch wire to give battery power to the clutch, 134 has higher pressure and will load the clutch more, even on the new one.
I have had to do this on all our trucks.
The compressor does not care which refrigerant it is pumping.
Again, if its cold, leave it be.
except for the relay.

 

[BrianX128]

Switched compressors, vacuumed system, only have two cans of 134a left tossed those in and it does the exact same thing as before.

I cannot understand how the pressure is dropping when the truck revs up. It does not make sense. I have a jumper to the clutch wired in and I forced it to run for two minutes straight while at high rpms and the air is so cold coming out of it but I'm nervous something will build pressure and burst.

I know it only has 24oz right now but much like before after one can was added the second didnt really do anything. I'm at my wits end here. Its better than nothing and does keep you cool but I can't help but feel like it just doesnt work right.

Literally everything is new now except the condenser which was put on new two years ago by the previous owner when he was gonna try and fix the under dash unit that used to be in it and he gave up and put the rubber plug back on and put the screwed the plastic caps over them and I pulled a vaccuum on it twice now and everything holds.

I just cannot see the failure point here. Just in case I'll type the route of my system in case I'm that dumb this week.

Evaporator suction port goes to suction line on compressor cant screw them up they're a bigger sized thread. Compressor discharge into top port on condenser, out bottom port into the in port of drier out of drier back into the smaller expansion port of the evaporator in the cab.

I don't understand why I'm filling the system on the suction side by the compressor per the instructions but the drier is on the high pressure side coming out of the condenser heading back to the evaporator and that's where the low pressure switch is at cycling the system..

 

[Thewespaul]

Pressure drop says you got a restriction. If you are getting a drop of pressure on the low side as flow increases (rpm increase) then your condenser is probably a bottle neck for the system. With these older systems, performance of the ac is more important than what your pressures are doing.

 

[BrianX128]

So in other fun observations after a few beers and staring at the truck, I put a test light on the wire that is coming from the evaporator that is supposed to power the low pressure switch, and when the system cycles off its cycling off because the evaporator quits sending power TO the switch, not because the switch itself is cutting off the circuit to the compressor..

Which makes even less sense.

Honestly it's funny cause it was 84 today and I was content in the cab with the temp but 22 clutch cycles just doesn't seem good for the compressor.

Dunno if this will help it make more sense to anyone. Tomorrow I'm gonna purge the system a third time and see if I can put the condenser that came in the kit on it to rule out some sort of a restriction in the current one on the truck just for the hell of it if I have the hoses to do so but first I might toss my jumper to the other side of the low pressure switch and see if it ever shuts the ac off.

The evaporator box in the cab had a thermostat on it and I'm wondering if it doesn't work right. I've tried moving the knob everywhere and all I can accomplish with it is to make it cycle more. Maybe it's not meant to stay on non stop but that's stupid.

 

[chris142]

The low pressure switch has an adjustment screw between the 2 male connectors. Adjust it counter clockwise to lower the cut out pressure. R134a should cut out @ 20 psi

 

[BrianX128]

I dont know if this switch has one honestly the back of it is flat and glued to the switch.

 

[hce]

Looking at the web page it appears these units use a thermostatic switch with a capillary tube that senses evaporator temperature. This switch will turn the compressor off and on dependent on the evaporator temperature to regulate the temperature. Cycling has to happen on this type of system.