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mark iv monitor r134a conversion not cooling

dusterbd13 on Tue July 07, 2015 7:55 PM User is offline

Year: 1964
Make: chevy
Model: el camino
Refrigerant Type: 134a

so i have built a system for my 64 el camino.

66 vintage mark iv monitor underdash unit
new expansion valve
r134 barrier hoses, all o-ring fittings except the two flare fittings for the underdash unit
new parallel flow condenser, as big as the radiator
new drier
vintage air manifold for Harrison r-4 compressor
used 89 vintage Harrison r-4 compressor, complete with the rest of the serpentine accessories (from extended cab fullsize truck)

the system was built by me, and initially charged with PAG oil and r134a straight out of the can. no vacuum applied. I never got the pressures up to where the gauge on the can dispenser said it should be, but the system was blowing about 10 degrees below ambient temperature inside the cab.

I then took it to a local shop for a line flush, proper oil, vacuuming, and correct r134 charge. it reads within spec on the gauges according to the shop, but blows ambient temp. the low side fitting coming out of the evaporator is cool to the touch, but not very. no condensation being formed. this is regardless of engine or vehicle speed, so I doubt its airflow related.

engine has a mechanical clutch fan.

what are my options here? did I miss something in system design? did they miss something with system pressures? anything I can do to make it work better? am I expecting too much?

thanks guys. usually I install aftermarket streetrod kits and sanded compressors, but wanted to do something different (and cheaper) this time. hoping im not going to regret this.

mk378 on Tue July 07, 2015 8:33 PM User is offline

And what are those pressures?

It's important to attach the TXV sensor bulb to the side of the evaporator outlet line (not the top or bottom) and insulate it from external heat. Attaching it incorrectly to the evaporator's inlet (right after the TXV) will cause exactly what you are experiencing.

Several components are sensitive to the direction of flow: condenser (in at the top out at the bottom), evaporator (in at the bottom out at the top), receiver drier and TXV according to markings.

Edited: Tue July 07, 2015 at 8:37 PM by mk378

dusterbd13 on Tue July 07, 2015 8:57 PM User is offline

I will check the expansion valve bulb location.

I will also insulate from external heat. the old insulation had failed, and I had not done anything about that yet.

the directions of flow are correct, surprisingly enough. never thought about the condenser orientation, and seem to have gotten lucky so far.

dusterbd13 on Tue July 07, 2015 8:59 PM User is offline

do not know what the pressures are, as the shop did not relate that to me. they just gave me the blanket "correct for conditions". these guys have always done right by me in the past, so even though I have no idea what the numbers are, id believe that they believe they are correct.

mk378 on Tue July 07, 2015 10:09 PM User is offline

If your fan clutch is worn out or otherwise poor airflow (missing shrouds, gap around the edge between radiator and condenser, etc.) the high side will be very high with a proper charge-- this often leads one to undercharge when they stop at the "correct" high side pressure.

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