Motorhome R134 Problems

[philipswanson]

The system in my Wanderlodge Bluebird bus has never worked right so I have done lots of work and spent lots of $$$ on it but its still not working very well. I put a new compressor from ACKITS on it, and spent over $1K to have the condensor and evaporator flushed out and repaired by Pacific Coolers in L.A. ( A new condensor was not available from Transair). I replaced all the rubber lines traveling the length of the coach with new swedged fittings, replaced the drier, as well as the cube type expansion valve behind the evaporator. I have been messing with this system for three years trying to get it working right and it still isn't performing.

In the process of trying to get it charged, its running 25-30 on the low side and 100-110 on the high side. After about 20 minutes of charging it still pretty much stays there. On evacuation, it held vacuum just fine so no apparent leaks. Output temperature at the vents is 55 degrees, only 5 below ambient. The compressor is cycling on and off (mostly off) constantly. Anybody have any ideas where to go from here?
THANKS!

[bohica2xo]

It can be very hard to diagnose a system at 60f ambient.

You indicate "20 minutes of charging" Trying to charge a large system with vapor is a waste of time. Try to get as much liquid in as possible while the system is in vacuum.

How much refrigerant is in the system right now?

What is the drive ratio for the compressor and expected compressor RPM at idle?

[philipswanson]

The system doesn't seem to take refrigerant as it should. Probably only has about 7-8 pounds in it. As far as liquid charging are we saying I need to charge the high side with engine off and tank inverted? I know you can't put liquid in to the low side or you will kill the compressor with a fluid lock. Compressor ratio is stock for this Transair system. Ratio of pulleys is 1.8:1. Crank pulley is 9" and the a/c compressor pulley is 5". RPM is 1200 at idle. Compressor is turning at 2160 (est)

[bohica2xo]

Well, with 8lbs of 134a in it, and the pressures you listed you should see cooling at that kind of compressor rpm.

Does the low side cycle on a pressure switch or a thermocouple on the evaporator?

The suction line on the evaporator should be cold - is it?

[philipswanson]

The suction line is cool but not cold. The high side line is very hot to the touch. The compressor cycles on and off on pressure switches. One for the high, one for the low. They are new and the correct pressures according to Transair.

[bohica2xo]

I am guessing the 1200 rpm is high idle on a diesel? What is cruising rpm?

With 8lbs of 134a circulating, and the low side cycling between 25 & 30 psi - something is getting cold. The cool suction line at 28 psi, and the hot compressor discharge @ 110 psi point to significant heat transfer. Is the evaporator air going someplace else? Re-heating from the heater?

.

[philipswanson]

The evaporator air is totally separate from the heater core. It is off and cannot mix. Cruising is about 2400 RPM. This morning, the low side is 25-28 pounds and the high side is 100. The compressor is staying disengaged and no cycling. I think it's still low on Freon but it doesn't want to take any more.

[philipswanson]

I put another 20 oz of Freon in and got the compressor to cycle a couple of times for sort duration. When the compressor ran, the high pressure side went up to 280-300 but as soon as it cut out, the pressure went back down to 110-125 and pretty much stayed there. No cooling at the outlets, just ambient.

[bohica2xo]

Static high side pressure of 110 psi is VERY different from running pressures. When you posed 110 psi earlier the assumption was that was with the compressor running.

Is the ambient temperature still 60f? If so you are seriously overcharged.

The low side should be at least static refrigerant pressure after standing overnight. Where are the low & high side service ports located on this system?

Diesel clowns rarely get the drive ratio right on accessories. That compressor does not produce full output until 3500+ RPM at the compressor shaft. I have fought this stuff with "truck" people for decades.

[philipswanson]

Yes, all pressures are with the compressor running. Service ports are easy to get to because I moved them to the rear, upper area. It's a diesel pusher motorhome. OK what should the static pressures read? I'll check them out. How can I tell if the system is overcharged?