1974 F100 cooling performance poor

[northbay]

Hello,

I bought a 74 F100 with a later model engine using a FS10 compressor, TXV, & parallel flow condenser of original size. The previous owner never tried making AC work. The compressor & condenser & evaporator were on the truck & they dont look new, but they were capped off. I removed compressor, drained 6oz oil & refilled with 6oz of new pag46. I replaced TXV & drier, made hoses, evacuated for couple hours & charged with 2 cans. Original r12 capacity shows 2lbs. My understanding is less r134 is needed when converting. Vent temp of 55 measured with ambient of 85. After running for 15min, low side 15-20, high side 275-300. I didn't want to add more refrigerant and drive up the high PSI. Used thermocouple clamp for the following line temps in degrees: Compressor In 70, Out 165. Condenser In 158, Out 123 (after drier as it's connected to condenser). Evaporator In 43, Out 55. I can get my hand in the heater box inside truck and feel the evaporator. It's cold at the bottom 1/4 only. The rest is not cold, only cool. Is the entire evaporator on a TXV system supposed to be ice cold?
BTW I tried attaching the TXV bulb to the evap outlet on top & at 9 oclock but it didn't seem to make any difference. Also it was clamped using a typical hose clamp (couldn't find the metal type clip) & was wrapped in cork insulation tape.
Any suggestions or advice would be appreciated.

thank you,
Ray

[Cusser]

Mist the condenser with water to see if the high side pressure at 2000 rpm drops considerably. If so, test the fan clutch.

[JohnHere]

I bought a 74 F100 with a later model engine using a FS10 compressor, TXV, & parallel flow condenser of original size. The previous owner never tried making AC work. The compressor & condenser & evaporator were on the truck & they dont look new, but they were capped off. I removed compressor, drained 6oz oil & refilled with 6oz of new pag46. I replaced TXV & drier, made hoses, evacuated for couple hours & charged with 2 cans. Original r12 capacity shows 2lbs. My understanding is less r134 is needed when converting. Vent temp of 55 measured with ambient of 85. After running for 15min, low side 15-20, high side 275-300.

The old oil that you drained from the compressor looked good? That is, it was amber to dark-amber in color (not black), and there were no metal or plastic particles in it?

There is no Rule of Thumb that says less R-134a is needed when converting a system from R-12. It might hold true, or it might not.

One method of converting from R-12 to R-134a is to "sneak up" on the correct charge by monitoring the center vent temperatures and pressures by adding one ounce of refrigerant at a time, starting at about 75-percent of the R-12 amount. Once you reach the point where both the vent temperature and pressures start to rise, you've reached the optimum charge. Stop adding refrigerant there and call it done.

However, it appears that you have a two-part issue going on, based on the pressures you posted: A low-charge condition, and a condensing problem. The latter should be solved first by using the method discussed in the previous post, and then you can continue charging using the method described above.