Converting factory AC to use R134a

[Andy4639]

Call these guy's they know there AC stuff and have kits for our trucks. I had their system for over 10 years with no problems.

http://www.classicautoair.com/

[Bigdav160]

I have a couple of questions if someone could address them:

- Would an AC shop need to pull apart under my dash, or in the heater core area that would require pulling a fender? I have brand new paint. It looks like the inboard section of the underhood HVAC box comes off. But are all the parts in there?

- When I buy a new pump and dryer from LMC, as I did, it has some oil in it. Would that be the old style or new? I poured it out but did not flush it.

What parts? The underhood box has the evaporator in it. Expansion valve and POA are connected to the evaporators inlet and outlet outside the box. There's also a door between the core and blower motor. It's control shaft sticks up out the top of the box.

I always replace the oil shipped in the compressor. There shouldn't be any need to flush it out.

[davepl]

Originally Posted by Bigdav160

What parts?

I guess a better way to ask is "When converting a truck over to modern refrigerant, are there any parts they need to access that are really invasive and that I should worry about them scratching stuff, etc?"

Thanks,
Dave

[Davidf]

No, all parts are under hood and in front of core support.

[davepl]

Say whaaaa? In front? Isn't there an orifice that has to be changed in the expansion valve and components removed to be flushed? Or can it all be flushed from the front?

I think I have a leak somewhere, one of my main concerns. I vacuumed it down and it would hold for hours but not overnight. A super slow leak is still a leak though. I was also worried how invasive they'd have to be to get at every component that could leak too.

[davepl]

I don't know if its the same as another local guy used that I saw, but had I known I would have eagerly sent mine off if only to get the case the right finish and the AC valves and lines the right silver, etc. It looks really nice. Mine has a little, um, "patina" by comparison because I could only clean and polish what I had.

And Andy, if I was too subtle, sorry, I wasn't really flaming you back. Just your font :0

[jimbosprint]

I think most leaks are usually in the old o-rings, not in the evaporator box. I plan to use the same evaporator for R134a, and replace everything else. There aren't any AC parts under the dash except the controls and ducts, so you should be able to get to everything with refrigerant from the engine compartment. I am not sure if it is possible to get the evaporator box off the firewall without taking off the fender, but I plan to at least remove the inner fender. You may not even need to take it off, but mine is full of leaves.

Old Air Products was helpful when I called and asked them about the upgrade to modern refrigerant. They have knowledgeable staff and parts that bolt on without customization.

[Acorn]

You can get the evaporator out without removing the inner fender. Just need to take one side of box off. ( engine side) but if you got leaves in there I would bite the bullet and drop the inner fender and remove the whole box. My .02c

[jimbosprint]

Originally Posted by Acorn

You can get the evaporator out without removing the inner fender. Just need to take one side of box off. ( engine side) but if you got leaves in there I would bite the bullet and drop the inner fender and remove the whole box. My .02c

Yep. That's the plan. Fix it right so I don't have to tear into it again any time soon.

[jimbosprint]

I painted my new compressor and drier so they will look more stock. Old Air offers the compressor in plain, polished, and chrome - why not black?

[coppertone]

I just finished redoing my ac,I also bought the pro6ten compressor, and the evaporator update kit from Old Air Products. Had to drop the inner fender wheel well to get to the bolts on the bottom of the evaporator box. My evaporator was full of leaves and it blew very little air before the tear down. Now it blows like it never did before. I had to remove the hood hinge and loosen the fender bolts behind the passenger door to put the box back on. Oh, I also replaced the condenser.I already had r134, but I wanted to replace every part on the ac system just for my peace of mind.

[Davidf]

Factory POA vs POA update (tube): Yesterday, I dumped (reclaimed) the R12 refrigerant and removed the Old Air Products POA update tube. I reinstalled the original POA valve that I calibrated to 29.5 psi. Evacuated, checked to ensure the system held vacuum (it did) and re-charged with R12. Man, what a difference. The original POA maintains very cold air out of the vents (did not measure actual temp, it was cold enough) at a constant temperature. The POS POA update tube would cycle the compressor excessively and the air would change from cold to warm constantly. Also, the off/on loading of the engine each time the compressor cycled was annoying. Further, I believe cycling the A6 compressor will severely reduce the life of the clutch/compressor.

So, moral of the story is to stay away from the POA update tube and install a genuine POA valve. I'm a believer.

[davepl]

So if I go to a shop and ask, should they know about the POA valve? Or is that not applicable to the older compressors?

I'm struggling to find a shop that knows a great deal and won't scratch my new paint. I've found one of each but not one shop that can do both!

[Davidf]

All the vintage GM air conditions (i.e. what was used in the '67-72 trucks) use a POA valve. So, any a/c shop that knows their stuff should be familiar with a POA valve. A POA valve lets the compressor run constantly by limiting the amount of refrigerant that can pass through the evaporator based on pressure. The colder the refrigerant, the lower the pressure. So, if evaporator is about to freeze up, the pressure drops below a given value of 29.5 psi (R12) and the valve restricts the refrigerant flow until the evaporator temp rises again. But, it never shuts off the flow and thus the occupant does not notice a rise in air temp at the vents. Make sense? I think I got that right. There is some interaction with the expansion valve as well. The EV meters the refrigerant change from liquid to gas.

The stupid POA update tube simply monitors refrigerant pressure and turns off the compressor if pressure gets too high. Not very elegant and during the off state, the evaporator gets too warm.

POA valves are readily available on Ebay and they are all the same no matter what vehicle they came out of.

[leddzepp]

I've read where some people have just by-passed the POA update valve switch so that the compressor never shuts off when the AC is running.

I bypassed the one on my 01 Yukon about three years ago when I got tired of the compressor cycling off. It works great with no issues.

[MARKDTN]

Originally Posted by leddzepp

I've read where some people have just by-passed the POA update valve switch so that the compressor never shuts off when the AC is running.

I bypassed the one on my 01 Yukon about three years ago when I got tired of the compressor cycling off. It works great with no issues.

You don't want to do that. If you make the compressor run constantly with an orifice tube system you will jack up the high side pressures and blow hoses among other problems. That low-side switch is there for a reason.

Your Yukon is probably low on refrigerant.

With a proper charge you should not see much cycling on that type of system.

[dkooi]

Does anybody know if you can use the factory AC brackets to mount the Sanden style compressor?

[leddzepp]

Originally Posted by MARKDTN

You don't want to do that. If you make the compressor run constantly with an orifice tube system you will jack up the high side pressures and blow hoses among other problems. That low-side switch is there for a reason.

Your Yukon is probably low on refrigerant.

With a proper charge you should not see much cycling on that type of system.

Been working for years now, I have no plans to change it.

Refrigerant is where it should be.

[kwmech]

bump to the front

[RedRoad]

Im planning on bypassing the rear A/C on the burb and just run the front system. Thinking on going through what I have and try to charge with R12 if possible. Since the compressor shows system requirement for the front and rear how many pounds should the front system need?

Anyone recommend a shop in the L.A. area that can run a LONG vacuum and possibly charge R12? If no charge how many cans from ebay are required?


If the R12 is not an option and I need to go R134 is the tractor A4 compressor the best way to go to keep the seal alive?


Thanks

[webfoot]

All that remains of my AC system is whats inside the box on the firewall. I guess I'll be sourcing a new condenser and all the brackets. Is there one aftermarket bracket I can buy to go on the modern replacement compressors? Do I have to get one specifically for this truck or can I use a late model? I assume the problem with this is they take different fittings.

I saw this bracket but not sure if it will work. http://www.oldairproducts.com/catalo...1030&Year=1970

[jimbosprint]

Speaking of brackets,

I had to slightly modify my stock compressor brackets to fit on the Pro6ten compressor I got from Old Air Products. The holes on the back bottom bracket were too close together so I drilled them a little oversized. One hole on the front compressor bracket also needed adjustment.

Another thing worth noting is that the bolts included with the compressor are not the same size/thread as the factory bolts. All of them work, but I need to get a couple bolt/nuts/washers for the top adjustable bracket and ground wire that were not included.

The clip that secures the hose with muffler to the front of the compressor needed to be moved and bent to work with the hose set. The clip that secured the POA valve to the evaporator case is too big to secure the POA adapter, but Old Air assures me it is not necessary.

All fairly minor things, but it isn't quote as "bolt-on" as Old Air makes it sound when you talk to them. I also think they should sell the compressor in black so it looks more like stock (I painted mine).

[jimbosprint]

I got everything put back together, just need to get to the AC shop for a charge of R134a. I sure hope this works well because it was a lot of work and $.

[jimbosprint]

Truck is at the AC shop getting a charge right now. I will report how well it works as soon as I know.

Here's some more photos from the project:

[picklito]

Jimbosprint,
Is this Drier- 21-4215A $65.00 from your post #20? That's the look I'm after.

Originally Posted by jimbosprint