1993 A/C system coupler strangness - advice sought! (1 Viewer)

John Young

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I've been posting about my unfortunate journey to replace the heater core on our 1993 Middle East 80. After cleaning and refurbishing the heater box and straightening the fins on the AC evaporator I've got things back together and it was time to vacuum the AC system to look for leaks in preparation for re-filling the system with refrigerant.

The only label under the hood says R12:

WhatsApp Image 2020-08-20 at 14.21.22.jpeg

But when I took out the expansion valve on the evaporator, it was an R134A type expansion valve, and it looked new. So new I decided not to replace it.

But when I started hooking up hoses I found only one quick-connect. On the high pressure side of the AC compressor:
1597948033744.png

The other side, the low pressure side coming from the evaporator inside the cab, had what looks like an ordinary schrader valve. I was able to get the hose from the manifold set to screw onto it:
1597948128759.png

And just for fun here is a photo of me using my weird, antique lab pump to pull the vacuum:
1597948202762.png

My question to the assembled wisdom of this forum is what about the schrader-type valve on the low-pressure side. Is this something I should replace? Is this normal for a 1993? Should I just close up that side and refill only on the high-pressure side? I remember that the schrader valve was not working very well--when I took the dust cover off it, the refrigerant hissed out. The AC was working fine before I had to take the whole thing apart, but I'm suspicious of the schrader valve.

This is my very first sojourn into the world of AC. I have literally no prior experience to draw on. Any advice would be gratefully received!
 

flintknapper

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I've been posting about my unfortunate journey to replace the heater core on our 1993 Middle East 80. After cleaning and refurbishing the heater box and straightening the fins on the AC evaporator I've got things back together and it was time to vacuum the AC system to look for leaks in preparation for re-filling the system with refrigerant.

The only label under the hood says R12:

View attachment 2410416
But when I took out the expansion valve on the evaporator, it was an R134A type expansion valve, and it looked new. So new I decided not to replace it.

But when I started hooking up hoses I found only one quick-connect. On the high pressure side of the AC compressor:
View attachment 2410419
The other side, the low pressure side coming from the evaporator inside the cab, had what looks like an ordinary schrader valve. I was able to get the hose from the manifold set to screw onto it:
View attachment 2410421
And just for fun here is a photo of me using my weird, antique lab pump to pull the vacuum:
View attachment 2410425
My question to the assembled wisdom of this forum is what about the schrader-type valve on the low-pressure side. Is this something I should replace? Is this normal for a 1993? Should I just close up that side and refill only on the high-pressure side? I remember that the schrader valve was not working very well--when I took the dust cover off it, the refrigerant hissed out. The AC was working fine before I had to take the whole thing apart, but I'm suspicious of the schrader valve.

This is my very first sojourn into the world of AC. I have literally no prior experience to draw on. Any advice would be gratefully received!

So.....looks like at some point the system was converted to R134a. There may or may not have been an 'adapter' on the low side port at one time. I'd recommend you put one on it. You can service your system 'as is' since you are able to connect to both high and low side service ports BUT....you already know you have a leaky schrader valve on the low side. So at the very least replace it....or you'll be leaking refrigerant right from the start.

You can charge refrigerant into the high side (into vacuum as a liquid, ENGINE OFF) but its unlikely you'd get the full charge into the system. The rest would need to go into the low side as a gas, compressor running, engine on.

First see IF the system will hold a vacuum like it is. No point going any further until you know that.
 

John Young

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Thank you very much for your reply and the information, FlintKnapper. I was able to connect to the low side with the 1/4" gas fitting that was on there but I've been suspicious of the schrader valve on the low side for a while--when I unscrewed the dust cover at the beginning of this project gas escaped. Later it seemed to be holding. But these were obviously old valves and easy to change. Originally I ordered on Amazon but the kit was going to take a couple of days. Then I thought of the Mr. Tire down the street--I've dumped a truckload of money with them and they know our crazy Land Cruiser addiction in this family so I gave them a call and one of the techs, Kevin, was kind enough to pass me a kit he had in his box along with the valve removal tool. My older boy and I changed out the schrader valves on both the high and low side and then we evacuated the system from both sides and left it overnight.

This is how the gauge read last evening:
1598015262370.png


This morning it was still holding about 30 inches of mercury:
1598014348224.png

What do you think? Is this good enough? I'm thinking yes.

Last evening I also dropped by the local parts store and picked up a quick connect for the low side and I just put it on.
1598015128914.png

I'm pumping it down again now for another 40 minutes or so.

I started thinking about compressor oil and decided to just leave well enough alone. When I pulled the evaporator I did loose a few drops of oil, but only a few drops and it was clean--very light gold in color. I'm not going to change the dryer because the AC was serviced in Dubai before I shipped it over about a year ago and my recollection is that they replaced it at that time. Also, I taped over the ends of the lines with rubber tape while the system was open so I don't think much water could have gotten in. I'm also not wanting to uncouple any more fittings than I have to for fear of introducing more leaks.

The next thing is to figure out how much R134A to put in the system... I've got several 12 oz cans of dupont R134A. Should I fill at least partly before I start the engine? Time to google a bit...

Thanks again for the reply!
 

flintknapper

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Thank you very much for your reply and the information, FlintKnapper. I was able to connect to the low side with the 1/4" gas fitting that was on there but I've been suspicious of the schrader valve on the low side for a while--when I unscrewed the dust cover at the beginning of this project gas escaped. Later it seemed to be holding. But these were obviously old valves and easy to change. Originally I ordered on Amazon but the kit was going to take a couple of days. Then I thought of the Mr. Tire down the street--I've dumped a truckload of money with them and they know our crazy Land Cruiser addiction in this family so I gave them a call and one of the techs, Kevin, was kind enough to pass me a kit he had in his box along with the valve removal tool. My older boy and I changed out the schrader valves on both the high and low side and then we evacuated the system from both sides and left it overnight.

This is how the gauge read last evening:
View attachment 2411153

This morning it was still holding about 30 inches of mercury:
View attachment 2411145
What do you think? Is this good enough? I'm thinking yes.

Last evening I also dropped by the local parts store and picked up a quick connect for the low side and I just put it on.
View attachment 2411152
I'm pumping it down again now for another 40 minutes or so.

I started thinking about compressor oil and decided to just leave well enough alone. When I pulled the evaporator I did loose a few drops of oil, but only a few drops and it was clean--very light gold in color. I'm not going to change the dryer because the AC was serviced in Dubai before I shipped it over about a year ago and my recollection is that they replaced it at that time. Also, I taped over the ends of the lines with rubber tape while the system was open so I don't think much water could have gotten in. I'm also not wanting to uncouple any more fittings than I have to for fear of introducing more leaks.

The next thing is to figure out how much R134A to put in the system... I've got several 12 oz cans of dupont R134A. Should I fill at least partly before I start the engine? Time to google a bit...

Thanks again for the reply!

Sounds like you are in good shape then and have approached this correctly.

You'll be using less R134a than the previous refrigerant (R12). IF your 80 series does not have the Rear Air option (available in some markets) then I would expect you'll end up using between 1.80 lbs and 2.0 lbs.

I think I would shoot for the lower figure and then check your vent temps.

Typically a fully charged system with R134a will show high side pressures about 2.25 to 2.50 times the ambient temperature.

So....if it is 90° F outside when you charge the unit....look for about 200-225 psi on the high side . Low side will probably be 35-40 psi.

Let us know if you run into any snags or need any additional help or information. There are several people on the forum well qualified to help out.
 

flintknapper

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If you have an FSM, it tells you pressures and amount of refrigerant to put in.

Trouble is...if his FSM is for a model that originally had R12...the amount stated will be MUCH higher than that for R134a.

Probably best to go by the amount recommended for later models (R134a) which is what I stated previously.

Hopefully, he has the correct PAG46 oil in the system too?
 

John Young

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Messages
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Trouble is...if his FSM is for a model that originally had R12...the amount stated will be MUCH higher than that for R134a.

Probably best to go by the amount recommended for later models (R134a) which is what I stated previously.

Hopefully, he has the correct PAG46 oil in the system too?
I have the rear AC unit, and also the AC-driven fridge between the front seats which are a couple of complicating factors. I ended up going with the original R12 label under the hood and then employing the conversion factor from this table:
1598194815854.png

This worked out to be between 1.193 and 1.287 kg of R134A, or between 3.5 and 3.8 standard 12 oz cans.

My son and I slowly filled the system after starting the car. Honestly, the most nerve wracking part was starting the car with the dash apart and a whole lot of things not connected. I wanted to fill the system and make sure it worked before putting the dash back because the PO's wiring for the radio and a bad old amplifier really, really sucked. I want to take some time and sort all that out.

I'm very happy to say that the heater core and the AC both work now. I still have some tuning to do. The heater control valve does not fully close at the moment, for example.

I really appreciate the advice from all of you.
 

flintknapper

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Joined
May 22, 2004
Messages
9,466
Location
Deep East Texas
I have the rear AC unit, and also the AC-driven fridge between the front seats which are a couple of complicating factors. I ended up going with the original R12 label under the hood and then employing the conversion factor from this table:
View attachment 2413390
This worked out to be between 1.193 and 1.287 kg of R134A, or between 3.5 and 3.8 standard 12 oz cans.

My son and I slowly filled the system after starting the car. Honestly, the most nerve wracking part was starting the car with the dash apart and a whole lot of things not connected. I wanted to fill the system and make sure it worked before putting the dash back because the PO's wiring for the radio and a bad old amplifier really, really sucked. I want to take some time and sort all that out.

I'm very happy to say that the heater core and the AC both work now. I still have some tuning to do. The heater control valve does not fully close at the moment, for example.

I really appreciate the advice from all of you.


Thanks for the follow up. Glad you got it working.

Rule of thumb conversion for R134a is: 80% of what the recommended charge was for R12. Then 'fine tune' it by adding or subtracting refrigerant until you meet the point of diminishing returns (Increase/Decrease of refrigerant no longer gives lower vent temps).

Good job!
 

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