1990 f-150 i-6cyl--accumulator FFOT type a/c system. System quit cooling recently. Found leaking quick connect and repaired. Added r12 and here's what happens: at 80F ambient temp, compressor will cycle about once every 10-12 secs. Each time the compressor engages for only about 3 secs. In other words, on for 3 secs, off for 10-12 secs (approximately). The guages (when compressor is engaged read as follows: low side drops to about 28 psi (and still dropping when compressor disengages), while the high side climbs to 230 psi(and is still climbing when compressor disengages). Compressor disengages when guages reach psi as described above. No cool air at vents. Compressor will not stay on long enough. Any ideas? Overcharged? Thanks.

 

What I would do at this point is jumper the pressure cycling switch on the accumulator to see if the compressor will stay on and watch pressure readings closely to make sure it does'nt get too high on the high side. Be ready to shut it down if it goes above 350. If it stays running are the pressures near normal and does it now cool? If so try replacing switch. If not what do the pressures do and does compressor still cycle?

 

Thanks for the info nitro24. Good idea jumping the cycle switch. Found the problem. Here it is in case anyone else has this problem. Jumped the pressure cycle switch and here's what happened: low side guage steadily dropped to -0 or vacuum level. High side steadily rose above 250 psi and was still rising when I shut it down. The high side line was barely even lukewarm. It should have been very warm. The line from the condenser to the evaporator was barely lukewarm, but, what I think is called the fixed orifice tube just above the evaporator inlet, was freezing. Problem? The fixed orifice tube was completly restricted with contaminants. It was a dirty gritty substance that felt almost like sand. Fixed problem by disconnecting the quick disconnect just above the fixed orifice (after reclaiming), removing the schrader valve core at the low side access next to accumulator and disconnecting large return line on low side (on the other side of accumulator). After disconnecting, plugged the large line by holding hand over it (with glove), used air hose with rubber tip and placed on low side schrader valve with core removed and turned air on. Air travelled through the evaporator and blew trash back out the orifice. Used a little wd40 to help break trash loose at the source. Blew it out for about 20 minutes, replaced o-rings and schrader valve cores, vacuumed the system for 30 minutes, recharged and now works brand new. I hope this info helps someone in some way. Please note that I make no warranty for this procedure nor do I advise anyone to try this. I am offering this experience only for informational purposes to those who may find it useful, and accept no liability whatsoever for any accidents anyone may have trying this.

 

Looks like you have already found what my next step would have been considering the pressure readings. Only comment now is think about where the debris came from. When this happens to the orfice tube is means that the compressor is failing internally. I would expect your fix to be short lived. If so I would recommend a conversion to R134 when it fails again.

 

Agreed. I wondered about the compressor and condenser after I read one of your other posts when you spoke of the "black death". However, I found and repaired a slow leak in the quick disconnect just above the orifice tube. I wonder, could contaminants enter the system in areas such as this where there are leaky, worn out o-rings on the low side. If so, this could account for the trash accumulating on the down side of the line (at the orifice). I drive my truck around on the job quite often, and it is constantly exposed to dust created by limestone (gravel). The contaminants reminded me of this when rubbed between the fingers. One more thing, would you care to elaborate on what specific type of compressor failure contributes to this "black death". Can this be repaired or the compressor rebuilt if it is caught soon enough? I enjoy reading your posts (Nitro94). Thanks for your input.

 

What you are seeing around the quick disconnects is A/C oil which has collected dust and dirt and thus makes it visible. Debris will not enter the system thru leaky o-rings. What you are finding in the orfice tube is material from the compressor rings and seals etc. They fail due to insufficient oiling usually due to loss thru the leaky quick disconnects. Preventive maintance would be keeping up with this oil loss. Otherwise compressors fail when they want to usually when its a 100 outside and you are out of money.