A/C Refresh – Making a Meat Locker

By: Bob Goodson
August 23, 2020

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Author: Michael Yount

Set about to recharge the A/C on the Corolla.  It was working, but only “coolish” temps.  It seemed to hold pressure fine.  Weirdness – only 1 R134 fitting on the low side of the compressor with a “high” (red) cap on it.  Based on that and the way it’s behaving, I think there’s a chance that it never had a vacuum pulled; damned likely that it never had a gauge set on it.  Looks like someone might have put just put one fitting on and then tried adding the freon.

Anyhow, picked up a fitting set, removed the Schraeder on the high side and installed without incident.

Pulled a vacuum down to 29″ (only took about 10 minutes – a good sign) and left it overnight – still 29″ in the morning.  Quickly replaced filter/drier, added 1oz PAG to replace that left in the old filter/drier, then pulled vacuum for an hour (30″) and charged using the gauges as a go by.

Didn’t use a scale because I had no weight spec for the bastard system in the car – I ‘think’ it came out of an ’81 Corolla – but not certain.  Had it been the dealer-installed Nippondenso unit back in ’73 it would have had the big York 2-cylinder compressor – and this has a nice, compact Denso rotary compressor.  Smooth and quiet.  Anyhow, I got to 20-25 psig suction, 200 psig discharge and around 40F vent temps (inside of the car glass was fogging on a humid morning – daddy happy!).  I’m guessing 15-17 ozs was all it took.  Little car sat and idled at 1100 rpm for about 50 minutes – never missed a beat, temps sat right on 200-205F.  Maybe my makeshift cardboard ducting and box fans helped — but the DCC-controlled cooling fan was doing its work just fine.

Now, when I went for a ride – I damn near turned the inside of the car into a freezer.  I left the temp gauge in place.  With more revs and more air moving across the condenser I saw 21F on the temp gauge within 5 minutes of leaving the house…. I AM NOT KIDDING.  The compressor wasn’t cycling off.  Didn’t get to play with the temp setting as much as I’d like — I’m guessing the expansion valve control isn’t working like it should.  And it’s an old system with no high/low pressure switch.  It will freeze your ass out of the car.  1973.  Who’d’a thunk?  Of course, those temps are a problem as it would have pretty quickly turned the evaporator coil into a block of ice.

For the time being, I’m going to put a switch in the compressor clutch wire – so I can manually cycle the compressor from inside the car. That’ll let me attend cruise-ins and such in cool comfort. Meanwhile looking to see if I can find replacement expansion valve and add a high/low switch.  There’s a threaded spot for a switch on the filter/drier.  I’ll have to pull the system down again to add it — but now that I know what I’m doing with it — a piece of cake + $15 of 134.  The other alternative is to spend $300-400 and buy a completely new under-dash unit (that’s what’s in the car) with a contemporary control system.  I think the compressor and evaporator are working fine.  21F temps and all….  Charge must be close – get over full or under full and warm air shows up.  This is anything but warm.  So I’m calling it a win – that needs a bit more adjustment.

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