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Switched back to r-12

mhfd112 on Mon August 04, 2008 5:26 PM User is offline

Year: 1977
Make: Chevy
Model: Truck
Engine Size: 350
Refrigerant Type: r-12
Ambient Temp: 95
Pressure Low: 40
Pressure High: 250

I recently came into a supply of r-12 so I thought I'd switch my old work truck back. R134a didn't cool real well when driving around town. I put in 3.75 lbs of r-12. I wasn't impressed with the results. I went for a test drive and the coolest vent temp I got was 55.

Kind of wish I had left it alone now.

TRB on Mon August 04, 2008 10:03 PM User is offlineView users profile

That truck should freeze you out with R12. Need more data to work with.

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Underdog on Tue August 05, 2008 9:02 AM User is offline

I fairly new to this and by no means an expert but here's a thought. My buddy has a mint 1982 Chevy pickup he converted to 134. Says it will freeze you out on the highway but in town not so. My suggestion was check the fan clutch or install an axilliary electric fan. You mention around town. Does it cool better on the highway?

mhfd112 on Tue August 05, 2008 8:27 PM User is offline

I don't believe it to be the fan clutch. I have changed it several years ago and it is still makes a lot of noise.

It always workded good on 134 early in the day and when highway driving. I have a water shut off valve in the heater hose.

I'll give it another road test in the morning and see how it does when it is a little cooler outside. It was a hot SOB Sunday when I put it back on r-12. Truck had been sitting out in the sun.

johnboy123 on Tue August 05, 2008 10:06 PM User is offlineView users profile

I hope this will be some help. first is a question - did you change your orifice tube back to the original?. second, if you did not then you would need to change back to the original to get the temp out the vent you are asking for. before you dump all of your R12 there may be another solution to the situation. what we are working for is to lower your pressures with out costing you a mint. disconnect your wires from the low pressure switch - remove your low pressure switch - 5/8 open end wrench - look and see where the plug was in and you will see a flat head screw - take a flat head screwdriver and turn it to you left 1/2 turn - this will lower the amount of pressure that is required to start your compressor to working - generally from 25 to 30 psi verses 40 psi. "recover" (yeah right) some of your r12 until you get you high side down to 180 to 240 - that should improve your vent temperature considerably. good luck

mhfd112 on Wed August 06, 2008 7:42 AM User is offline

I don't remember for sure which orifice tube I have in there. There is a good chance it could be a blue one. I can recover the charge an change back to white if it comes down to that.

mk378 on Wed August 06, 2008 10:20 AM User is offline

Were you using PAG or ester type oil with the R-134a? PAG oil reacts with R-12, so it must be completely removed from the system to convert back.

mhfd112 on Wed August 06, 2008 1:42 PM User is offline

I used BVA 100.

I put the white o-tube in this morning. I got about 3 1/2 lbs of freon recovered using the storage tank on ice method. Pretty good results considering the total charge was 3 3/4 lbs.

I weighed the storage tank before putting the freon back in the system. This time I put in 2 lbs 12 oz. On the road test it got down to 44.6 at the center vent. I don't know if the o-tube fixed the problem or using less freon. At idle it will get up to the mid 50s.

Pressures at high idle were 235 high and 36 low. Temp in front of the condenser was 100.

mhfd112 on Thu August 07, 2008 10:54 AM User is offline

This morning it was about 75 degrees and raining. On the way to work center vent temp got down to 31.2 before the compressor cycled off.

I think I may need to reevaluate the condition of my fan clutch. Yesterday the vent temp was 44 on the highway and when stopped it would go up into the 50s.

webbch on Thu August 07, 2008 11:01 AM User is offlineView users profile

You can check for an airflow problem by misting the condenser with water when the engine is fully warmed up and seeing if the high side pressure drops like a rock. If you're not certain about clutch "feel", this may help.

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