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high r12 pressures

dschmit on Wed July 02, 2008 1:14 AM User is offlineView users profile

Year: 1970
Make: chevrolet
Model: chevelle
Engine Size: 454
Refrigerant Type: R12
Ambient Temp: 85
Pressure Low: 35-40
Pressure High: 350-400
Country of Origin: United States

Factory air car. Original components (compressor,condenser, drier, hoses) removed before I got the car. I installed a Seltec 15hd compressor, 15.5"X27.5" parallel flow three pass condenser (china) and made custom hoses, tested POA and i am using original evaporator(flushed) and expansion valve. First condenser leaked, but after I originally charged the system with 3lb. R12 pressure were good 35 low and 180 200 down the road everything was good cooled to 39 degs. After replacing condenser that leaked I flushed the entire system again and drained the compressor and then added 7 oz. oil to compressor and charaged to 3lb. again, but this time low pressure is 35-40 and stays there but high @ idle is 185-200 coole to around 40 and as rpm's increase to 2500 high side goes to 380-400 and will kick out. While the high pressure is climbing, if i unhook the blower, the pressure falls rapidly down to 185-200. I am guessing that I might have a restriction some where. The trinary switch is located on the drier two feet from the condenser. Could I have a bad condenser? Also when i unplug the blower the low goes to 30 and stays there high falls to 125-130(I don't know for sure how low). Rear half of POA and compressor suction line @ compressor frosts over. Also while driving highway speeds with high side climbing to 300, if you let off of the throttle the presssure come right down. Driving slow in town, It seems to cool fairly well - 45 deg or maybe a little less.

Edited: Wed July 02, 2008 at 1:22 AM by dschmit

mk378 on Wed July 02, 2008 8:50 AM User is offline

Some people have had trouble with the Chinese condensers. Is it made of aluminum, or brass or steel? The latter two will give inferior performance. Also you could check for blocked tubes by feeling for cold spots on the condenser. The factory specified charge may be too much considering the new condenser has smaller internal passages. Also need to be sure of the oil charge.

dschmit on Wed July 02, 2008 8:58 AM User is offlineView users profile

aluminum. I didn't check individual tubes, but using my hand I did not feel anything too extreme from inlet to outlet, probably about 40-50 deg.

94RX-7 on Wed July 02, 2008 2:35 PM User is offline

I would suspect that you're overcharged as well. That behemoth tube and fin condenser can hold WAY more liquid refrigerant and not cause pressures to go crazy than the parallel flow unit you've got on there now. I would recover a pound of refrigerant then see how the system performs. From there you're just going to have to increase or decrease the charge depending on the pressures and vent temperatures you're seeing.

dschmit on Wed July 02, 2008 11:34 PM User is offlineView users profile

thanks mk378 and 94rx-7 for your replies. I did recover one lb. r12 and pressures dropped drastically. I then put 2 oz. back in because I had bubbles in the sight glass. 95+ degs. ambient today and gages were 36 low 125-130 on the highway. in town the high side creeps up to around 225 and still have some bubbles in the glass, but cools to 45-46 on highway. I think I will try this. We are leaving for the Des Moines GoodGuy show in the morning. thanks again for your help.

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