AC went "poof"

[kensousa]

So I'm learning (the hard way) about air conditioning.
I picked up a '71 Cheyenne that was a factory AC truck.
It was missing a compressor and the PO had taken most of the other parts off and handed them to me.
So with some pictures from this board, and a lot of trial and error, I was able to find and mount a compressor, re-mounted the condensor, and re-mounted the hoses, brackets, etc.
I'm pretty sure that I had everything hooked up correctly......

So I picked up one of the home conversion kits to change it from R12 to R134.
Put the low pressure adaptor on the low pressure side.
Fired up the truck.
I'm missing a switch that fires up the compressor, so I put a hot lead jumper to the compressor.
The compressor clutch pulled in.
Everything looked ok.
I put one can of the R134 into the low pressure side.
Pressure rose to 10 ish PSI.
I put a second can of the R134 in.
Pressure rose to 15 ish PSI.
I didn't want to put any more in, so I sat there and let the truck run (with compressor clutch engaged) for a bit.
2 to 3 minutes later, I hear this fairly loud "Boom" and see oil and coolant leaking out of the evaporator both from the firewall side and inside the cab.
Not dramatic leaks, but definitely stuff "oozing" out.
I pulled the inside duct work and the evaporator looks ok, at least with a cursory look.
Other than the obvious advice of "take it to someone who knows what the hell they're doing", can you guys give me some tips on what to look at next?
I'm trying to avoid pulling everything off of the firewall and pulling the evaporator out, but wonder if I haven't blown something up that's serious in there.
thanks

[leddzepp]

I take it you skipped pulling vacuum on the system?

[eldogg]

It could be a number of different things. (clogged evap, too much high side pressure,bad compressor,etc etc) Let me know if I can help.

[68gmsee]

Originally Posted by kensousa

So I'm learning (the hard way) about air conditioning.

.............. I hear this fairly loud "Boom" and see oil and coolant leaking out of the evaporator both from the firewall side and inside the cab.

...............Other than the obvious advice of "take it to someone who knows what the hell they're doing", can you guys give me some tips on what to look at next? ............ thanks

Part of the fun of working on the old trucks. A similar thing happened to me years ago while working on my mother in law's old car. Blew the compressor. I told her must have been moisture in the lines. She took it in to the experts and it cost her $850 to fix. Still don't know what I did wrong.

Welcome to the site.

[sleepertruck72]

Before you add R134 (or any refrigerant for that matter) into an A/C system you need to I.D. the refigerant that is in the system. R134 and R12 are mixable but not compatible... Lets assume the R12 was pulled out of the system with a vacuum pump. To me it sounds like the compressor did not cycle on/off and the pressure went too high for too long. 2-3 minutes is a long time to run the compressor straight without cycling on/off. Of course I could be wrong, Ive had ALOT of Mickeys tall cans tonight and the A/C class I took was a long time ago Anyhow Im interested in finding out what happened and hopefully its not too serious. Even if the parts were new, you should pull a vacuum on the entire system to ensure any moisture is boiled out avoiding contamination of the refrigerant... You also need to know how much refigerant the system needs and have a machine charge it to get an accurate charge. ..

[kensousa]

Yeah, I'm cheap and figured one way to learn is trial and error. I'm learning A LOT....

I did not use a vacuum.
I assumed that since this was all in different pieces and disassembled, there would be no old R12 in there.
It now makes sense that there would be a high pressure regulator sorts, disengaging the clutch to maintain pressure. I have a copy of a schematic, but can't remember seeing a pressure regulator anywhere.
I guess since I ran it for that long with a hot wire, that I likely ran the pressure too high and blew some lines in the evaporator or connections in there somewhere?

thanks

[ChevLoRay]

If you didn't pull a vacuum before starting to charge the system, you had numerous contaminants in the system, along with whatever was in the ambient air, like the moisture in the air.

But, a lesson learned....is a lesson.

[68gmsee]

Yeah, I've found out through the years that you can get by for a short period without pulling a vacuum on an a/c system but it can cause some internal damage later. Moisture and refrigerant creates a corrosive atmosphere and damages the components.

When you pull a vacuum in the system the moisture evaporates and is sucked out. Sometimes you can do a flush and clean any other contaminants in the lines out as well.

First thing is to find the leak. If it's a small one that's hard to find it might be better to bite the bullet and have a shop that has detection devices locate it for you. If you feel like learning more, try a can of leak detector and see if you can see it coming out.

[stsalvage]

well I heard the story's about 134A and R12 I hear that 134A if you lose a little your system goes Hot.But with R12 you can lose almost half and it will stay cool.Now when you have a open system I've been told to Change the AC Receiver Dryer that is the most important thing to change.Most shops do not want you using the leak detector stuff it will jack up there system and it can cost you 500 to 1000 if you lie to them.they will ask you point blank if you used any Leak detector dyes it really Plugs up there machines and cost them 2000.00 to have then cleaned cus it contaminates other peoples systems.So be for you put that leak detector in ask a shop to see if that dose not work will they reject your car from getting any Air conditioning services.

Most important thing to change is the DRYER

i HAVE A 1971 CHEYENNE THAT IS FULLY LOADED AND IT DID NOT HAVE THE AC BRACKETS AND NOW I HAVE THEM ALL AND IT LOOKS REALLY GOOD

[stsalvage]

NB#2 PIC'S OF Air conditioning BRACKETS

[kensousa]

Obviously finding the leak will be my next task.
I think I'll bite the bullet and dive into removing the evaporator so I can get a closer look.
Knowing what I did wrong is important too. Is there in fact a pressure regulator that drives the compressor on and off to maintain a certain pressure level?
If so, where is it, and what does it look like?

thanks

[dingesb]

I worked on tractors for quite a few years and from what I can tell this system is similar to the old John Deere compressor. These would have had an internal diaphram system that controled the pressures. If it got too high, these had a external pressure pop off system that released pressure until the compressor was satisfied. I wish that I could offer more help, as air conditioning was my specialty on the older tractors and now I have my own home a/c repair business, but I'm just not at all familiar with these systems. I do own one, but I've never even seen the pickup yet...lol...yeah I know that's bad right? I should be back home next weekend to look over my sisters HVAC system before they move her new house. I will try to get down to the '69 and have a once over on the system. I know there's alot of guys with factory on here so hopefully one of them can help you out a little better!

[1972RedNeck]

Originally Posted by dingesb

I worked on tractors for quite a few years and from what I can tell this system is similar to the old John Deere compressor.

Very similar indeed.If you need to get a new compressor I would a John Deere compressor even though they are reman. Knock on wood I have never seen one go bad.

[mrein3]

I just finished up re-habbing an old stock R12 system to run with R134a.
Look here and scroll down to post #8.
http://67-72chevytrucks.com/vboard/s...d.php?t=478564
Don't skip any of the steps.
ALL of the old oil needs to be flushed.
The POA MUST be adjusted for the different refrigerant.
This system does NOT cycle the compressor. When you turn it on it stays on until you turn it off - or you blow it up.
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