720 AC revival

[powderfinger]

I have been driving my 85 720 for a year and a half now and am to the point where I'd like to get the factory AC working. It is still configured for R12. I tried adding some oil and propane (don't judge lol) to see if the compressor was working and crossed my fingers that it would everything would just work. Of course it didn't. As soon as I started to charge the system the pressure went from 0 to really high making me think something is stopped up. One good note is as soon as the pressure went up the compressor came on so that works.

 

I tried blowing air through the evaporator with my air compressor and no air will pass through it so I am guessing that is clogged. A few questions:

 

1. I can't find an expansion valve anywhere. Where is it located on these trucks?

2. Is there a reliable way to clean out some of things in the current system without replacing them? I would like to avoid spending too much money if possible. 

I will certainly replace the drier and expansion valve (if I can find it lol) because they are cheap, and of course the evaporator because it is clogged. Mainly I would like to avoid replacing the condenser and the compressor. Although I have a feeling as old as the compressor is it will probably work for a while and then fail which is what happened to my old civic when I tried reusing the old compressor.

 

 

Edited June 21, 2020 by powderfinger

[NC85ST]

The expansion valve is under the dash in the box with the evaporator. Getting all of the clips off of that box is a pain. If I remember right there are at least 2 of those clips on the back side of that box, between it and the firewall. 

[Charlie69]

It is easiest to pull the blower box first and the the AC evaporator box and then the heater core box.  While all of these are out test, clean, and reseal all before re assembly.

Edited June 24, 2020 by Charlie69

[powderfinger]

Thanks guys, I figured it must be under the dash. Going to try to get this thing working in the next few weeks.

[Charlie69]

On the AC evaporator box you first Disconnect the wires and then pull the hoses from the evaporator tubes in the engine bay coming through the firewall.  Then you remove the phillips screw holding the retainer plate and the rubber gasket that hold the evaporator tube to the firewall.  The remove the phillips/10mm screws that holds the evaporator box to the firewall inside the cab.

 

1985 720 720 heater, AC, and blower boxes.

 

720 heater, AC, and blower boxes installed in my 1966 520.

 

 

[giantcone]

Hey Powderfinger, the propane idea is not bonkers, but I recommend that you look into R-290 (which is propane formulated for use with refrigerant systems). It is compatible with R-12 & R-22 systems from what I understand. I've seen bottles and cans of it for sale on ebay. Perhaps a bit more pricey than propane intended for combustion (grilling/heating).

 

I have a 720 that came without A/C from the factory. I'm thinking about putting in the components for getting an A/C in the truck.

If you need to replace the evap core, I've seen some new aftermarket ones going for around $60. I'm a bit uncertain about compatibility between a 1985 720 and the later D-21 models, so I haven't pulled the trigger on buying parts yet. I won't hijack this thread, but I may make a new one (or search for an already existing one) about attempting to "shoehorn" in a factory A/C system.

[Charlie69]

720 and D21 AC evaporators and condensors are different.

[powderfinger]

Good times 🙂 After cleaning all this mess up, installing the new expansion valve and drier, and charging system with propane the air is blowing COLD. Unfortunately, after running it for a few minutes the compressor starting making some pretty nasty noises so looks like I am going to need a new compressor. I kind of expected that from a 35 year old compressor that hasn't been used many years. Same thing happened when I tried to get the AC working on an old Honda I used to own except I just went without AC on that car.

 

 

 

 

[powderfinger]

I didn't realize these trucks came with two different compressors and mine is the one you can't seem to get anymore. At least not at any of the parts stores or on RockAuto. Mine is a Nihon DKV-14B and most places carry the replacement for the DKV-14C I believe. They use different AC hose connections. Of course I didn't realize that until I purchased it so now I'll have to return it. 

 

After removing the old compressor I went to dump the oil out of if and it didn't seem to have much in it so I drained it and filled it back up with Ester oil and reinstalled it and crossed my fingers. I then pulled a vacuum and charged the system with R134 instead of the propane, hoping it would cool good enough. I read a lot about propane causing the system to freeze up if you don't mix it with butane.

 

So far compressor seems to be working ok, no strange noises but system isn't getting as cool as I would like which is what I feared using R134. Had the same issue converting a late 80s Jeep Comanche pickup once. Yesterday evening it was around 90 degrees and the vent temps would only get to 50F driving at 50MPH. Idling it would be 60F. 

 

I wonder if I could find a larger condenser off another vehicle that might work better? Other option would be to pay up for some R12 but not sure I like that option for future use if there is a leak or anything which with a 35 year old vehicle is probably likely at some point.

 

My compressor

 

 

The one all the stores carry.