R12 TO R134 Conversion

[chengny]

If the outlet on the condenser is cold, my guess would be the condenser itself has an obstruction. Where else could there be an obstruction?

Exactly, sounds like you're "all over" (i.e. completely understand) this issue. I would guess there is some trash stuck in one of the bends in the outlet riser. The obstruction will act like a metering device. That should make it easy enough to locate - the tubing should change from warm to cold right at the point of the blockage.

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This opening around/through this obstruction must be fairly large. If it were small, your cooling capacity would be severely limited.

Another question, if I decided to put a variable orifice tube instead of the regular one I put in, do I have to evacuate the system and pull vacuum and recharge again? Or can I just swap them really quick like?

Yes, you can do this on the fly. There will be plenty of refrigerant still entrained in the oil. This takes quite awhile to boil out. As it boils out, it will maintain a slight positive pressure within the system. Be a good idea to do the change on a warm day. The refrigerant will boil out of the oil faster and this will keep any moisture/non-condensables from contaminating the system.


If the residual refrigerant boils completely out - try to close up quickly. Don't forget, that big silver thing is a filter/drier. It will absorb limited amounts of moisture. But there is no easy way to remove any air (non-condensables) that get in - while you have the piping open to atmosphere.

 

[VAL]

If the outlet on the condenser is cold, my guess would be the condenser itself has an obstruction. Where else could there be an obstruction?

Exactly, sounds like you're "all over" (i.e. completely understand) this issue. I would guess there is some trash stuck in one of the bends in the outlet riser. The obstruction will act like a metering device. That should make it easy enough to locate - the tubing should change from warm to cold right at the point of the blockage.

You must be registered for see images attach

This opening around/through this obstruction must be fairly large. If it were small, your cooling capacity would be severely limited.

Another question, if I decided to put a variable orifice tube instead of the regular one I put in, do I have to evacuate the system and pull vacuum and recharge again? Or can I just swap them really quick like?

Yes, you can do this on the fly. There will be plenty of refrigerant still entrained in the oil. This takes quite awhile to boil out. As it boils out, it will maintain a slight positive pressure within the system. Be a good idea to do the change on a warm day. The refrigerant will boil out of the oil faster and this will keep any moisture/non-condensables from contaminating the system.


If the residual refrigerant boils completely out - try to close up quickly. Don't forget, that big silver thing is a filter/drier. It will absorb limited amounts of moisture. But there is no easy way to remove any air (non-condensables) that get in - while you have the piping open to atmosphere.

Thanks Chengny.

 

[THart87]

Hi, i know this thread is old, but it has been the best one I have found on the internet so thanks for the description. Hopefully, you guys still get notifications about it. I am looking at doing this same conversion on my 87 K5. I just recently bought the truck and have been going through it. The AC System is completely empty. I pulled the orifice tube and the filter had metal shavings in it so I think it had a compressor failure. Going to replace the compressor. Should I replace it with the same compressor or get a different one that would work better with the R134a? Also if I change the compressor do I need to change the other components? I also bought a new drier and orifice tube.

 

[84stepside]

No component changes are required to switch over from R12 to 134a. All the currently installed parts can remain and will work just fine with a 134a charge. You might want to change to replace the filter drier and the expansion tube. The filter drier is that big silver canister attached to the evaporator housing. The expansion tube is accessible by opening the fitting that connects the liquid line to the evaporator inlet.

Filter drier:

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Expansion tube:

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Couple of notes:

You will have to dump the remaining R12 before anything else is done. You can release it to atmosphere, but certified shops cannot.

They have special re-re (refrigerant recovery) equipment that captures the R12. When they have a full bottle it gets sold to a facility that purifies and repackages it for re-sale. The production of new R-12 was banned worldwide years ago, so the only source is what can be reclaimed.

Anyway, if a shop does this conversion, that recovery process will trigger an extra charge. If you do it yourself it is free.

Whatever way you do it, after the system gets dumped, it will need to be flushed, evacuated and recharged with 134a.

Flushing is required because the oil used with R-12 is non-compatible with the oil used with 134a. There is a specific, involved, expensive way to do this - or there is the easy way. Provided your system is not being changed over due to a "black death" casualty you can do it with all the components in place and using just compressed air.

Black death is just a term used to describe a refrigeration system that has been disabled due to a catastrophic failure of the compressor. All the components and connecting tubing/hoses are contaminated with burnt (caked on) oil and all the metal particles that resulted from the compressor failure.

Release all the tubing fittings that connect the 3 main components (compressor, condenser & evaporator). Remove the suction/discharge hose manifold from the back of the condenser. Pull the existing expansion tube from the tubing that leads into the evap. Remove the filter drier.

Using 100 psi compressed air at a good volume:

Blow the residual oil from the condenser and evaporator coils. Do this in in both directions. Repeat until you feel that the bulk of the old oil is removed.

Blow out the liquid line that connects the condenser to the evaporator.

Blow out both compressor hoses.


Understand that the old R-12 oil is not like "poison" to the newly added 134a - it just does not circulate as well. So if there is a bit that remains in the system it will not be an issue.

That's it for flushing.

Using new o-rings at the fittings, replace your filter drier and expansion tubing.

Add PAG 100 oil in quantities as below and close the system up.

•Compressor- (1 ounce)
•Evaporator - (3 ounces)
•Condenser - (1 ounce)
•Accumulator (2 ounces)

Evacuate, leak check (system should hold 28" Hg overnight) and charge with about 50 ounces (4 cans) of 134a. You will have to jump your low pressure cut-out switch to get the first 2 cans in. After that the system will have enough pressure to allow the low pressure switch to operate normally and keep the compressor running.

You will need to buy a set of adapters for the service ports so you can charge and attach your gauges - if you have them. The adapters just screw on to the existing service ports.

Great post. Just don’t use PAG oil. Use Ester oil. That way it’s compatible with both R12 and R134a.