John, I hope the following advice is applicable. If a system goes to zero
pressure, you will have to jumper the compressor to make it start to get a
certain amount of refrigerant in the system. After that it will start
working by itself but not until. As I recall you just find the connection
and run a jumper wire to ground. I have done it, can't quite visualize it.
It has been a long time.

Jim

On Wed, Apr 26, 2017 at 7:21 PM John Rodgers <jrodgers113@gmail.com> wrote:

> With the summer heat coming on, I'm back on this.
>
> The story: I had never even turned this AC on the years I have had it, rut
> set about to resurrect it. When I first turned it on, I did so with
> ignition   in accessory mode, not actually starting the engine. The AC
> condensor fan did not turn on as it should. I figured the refigerant
> pressure was so low or non existent, that the system was in automatic shut
> off mode and would require enoungh refrogerant pressure to trigger the
> relay to turn the system on. The car had been in mothballs for several
> years, but to  my surprise  the system still had some R12 in it. I was
> running down the road, whe  I heard a kapow in the back of the van. I could
> hear a whistling sound, an on checking, I discovered that the trinary
> switch which is essentially the high/low pressure switch, had blown out and
> dumped the refrigerant. Replacing the switch, which is ni the left
> D-pillar, was no big deal, but I doing so, I discovered the real culprit.
> The schrader valve port to which the trinary switch mounts had given up the
> ghost. The 'O' ring in the valve had dry rotted letting the pressure out
> into the trinary switchsince I would be adding newer refrigerant I had the
> system evacuated and that blew out the trinary switch rubber seal. Since I
> was going  to convert the system and run  H152a in it, i had it vacuum
> checked. It held at 29 in. Hg. I started the engine, turned on the AC, and
> started adding the 152a. The compressor did not start. I am at a loss where
> to go next. A new receiver/drying was installed. I did not install an
> expansionvalve. Just hoping to get by.
>
> Suggestions!!
>
> Thanks!
>
> John Rodgers
>