Sorry for another AC thread but I think I’ve exhausted reading the threads and I have limited AC knowledge but have made progress eliminating issues.

Baseline: Unknown condition. Was converted to 134 at some point. Internal flaps all appear to work properly. Temp slide seems to function properly.

Step 1: Clutch not engaging: Checked continuity and volts at Freeze Switch. OK. Checked Pressure Switch at dryer. No Continuity. I suspect that the switch is good but pressure low – meaning its functioning. By passed the switch. Clutch engages. Cool

Step 2: Checked the heater valve. Vac pulls the valve closed. Have not removed it to make sure it’s functioning internally as per some threads on issue.

Step 3: Hooked up AC gauges (first time). With engine off, cold, LP is 15lbs, HP is about 15-17. Seems like a good sign since it’s got pressure ??

Started engine: LP dropped to (-20); HP started increasing but then dropped to 0.
Let engine run for 10 minutes. Saw some/minimal bubbling in drier view glass.
Turned off engine: LP back to 15 and HP back to about 15-17.

What’s step 4 ?

 

add refrigerant its low.

FWIW any areas of the system that have an oily/dirty accumulation are leaking areas.
Pay attention to the high pressure line ( small diameter line) where it passes under the Hot post area.
the factory used a flex line here and this line is known to leak thus it needs to be replaced.
Greg Brown sells a replacement kit where the old fittings are cut off and new ends silver soldered on then a new line screwed on.

 

Merlin - I checked and don't see any leaks but next time will add a shot of dye.

I added a 12oz can this morning. Now the site glass has lots of bubbles/action and the line into the expansion valve got ice cold.
With engine running (60deg outside) I got the pressure up to about 2 on LP and 35-40 HP. Decided to let it sit for a while.

Add more refrigerant ?

 

NOTE these figures are for R 12.
NOTE you would reduce the amount by 20% if using 134
yes add more refrigerant.

With R 12 your system needs just about 4 12OZ cans to filled.
NOTE with rear air it takes about 43oz. to fill it,
(With no rear air it takes about 36 oz.)
if you use 3 1/2 cans of R 12 it will be close to full.
NOTE if using different refrigerant than R 12 then reduce the amount installed by 20 %

 

Added another 12oz bottle. I thought the 134 should just easily flow in but I have to constantly adjust the valve on the can and shake the bottle. In any event, I now have pressure at about 20LP and 75HP. I disconnected the pressure switch jumper and the compressor now stays engaged ! Cool. And, yes I seem to now have cold air - but it was only 60 here yesterday. I'm going to see how it is for a few warm days and then add another can.

Thanks Merlin !

 

Don't run the system any longer with the PS jumped because the system needs a full charge of refrigerant to move the oil through the system otherwise
you could damage the compressor.

4) Depends upon how far you want to take it. A short cut would be to add refrigerant.
The medium road would be to recover the refrigerant, put in a new drier, evacuate, charge, test and sniff for leaks.
Longer road would be to recover refrigerant, liquid flush (AC Lines, condenser, evaporator with TEV off) replace every o-ring, add refrigerant oil, put in a new drier, evacuate, charge, test and sniff for leaks.

And, verify fresh air flap actuator works.

 

Just curious: If most of the R134 leaked out, I'm wondering if most of the oil went with it. You're doing crapshoots here of course, but the system might be low on oil as well. Also pressure numbers need ambient air temps to mean much.

C

 

On a system that has been running (not a fresh install), the refrigerant oil is spread out through the system (lines, condenser, compressor, drier and evap's).
Depending upon the severity of the leak you could have:
A) slow permeation, trickle, compressor nose seal (not so much refrigerant oil is lost, less than an ounce),
B) erupted hose (an ounce or two at best might blow out)

A worst case scenario, the car is 30 years old, its been 'topped off' with refrigerant many times by past owners or shops but additional oil (an ounce or so) has never
been added.

There are some 'general rule of thumbs' for adding oil when replacing components to play things safe, and they vary,
but you can guess safely with:
compressor, 2-3 ounces
drier, 1 ounce
condenser, 1 ounce
evaporator(s), 1 ounce

20LP and 75HP with 24 oz.... the pressures at 60F says you are undercharged, however the smart thing to do is recover the refrigerant, evacuate properly and charge with the known charge,
for an 86 R134a single evap about 30 oz and dual evap about 36 oz. If you had a full charge at 60F ambient you'd expect somewhere near 144 on the high