Air conditioning compressor 68 L-36

[Charles F.]

I have a 68 L-36 with factory A/C. The compressor (after-market) is failing and needs to be replaced. Where I can, I have gone the "numbers matching" route and therefore don't want another after-market unit. What is the best choice for both functionality and to maintain judgeability ? Where do I get that choice ?

The foil label will obviously have to be purchased and re-created. From the archives, it seems the type face should be Courier, 15 point; is this correct. The build date is April 1968; what information will be needed to correctly complete the label ?

I'm told that the system has R-12 fittings (appearance) but is actually a R-134 system.

I have been in touch with Classic Auto Air in Florida as I initially thought it was only the POA valve. They can supply a correct, re-built one for $169, with a core deposit of $45.
I've read reams of A/C material in the archives but am still confused.

Thanks.

Chuck

[Edward J.]

Re: Air conditioning compressor 68 L-36

Charlie what are the symtoms of the system that make you beleive the compressor is failing?

Is the present compressor the correct looking (A-6) ? .

about the only thing that fails on the a-6 compressor is the gas seal that retains the R-12 refrig. or if the compressor does not have enough oil in the system.

[Charles F.]

Re: Air conditioning compressor 68 L-36

The compressor has been tested by the mechanic and is not putting out enough (I'm no mechanic but he said something about the pressure differentials, intake versus output being low, with the output side about 10 when it should be 30...but I may not have understood everything). There is a restriction in the system and it doesn't blow cold. The restriction is why they thought the POA valve initially,which was restricted. Also, they substituted another (known good) compressor for mine and then the system seemed to have enough pressure (but for the POA valve).

For what it is worth, there may have been a mix up with the refrigerant. The restorer was supposed to (as I asked) have kept the R-12 system, but I just learned that there are R-12 fitting mated to R-134. I had R-12 put in the system about six months ago and now know it should have been R-134. Either way, the system never blew cold.

Chuck

[Edward J.]

Re: Air conditioning compressor 68 L-36

Chuck, have the system flushed, recharge system,with R-12, Im not sure the r-134 refig. will work very well with the old systems, pressures wil be different.and cooling is not the same as r-12.

alot of times the system is low on refeg. the system does not work very well, look for soures of leaks, sometime the gas seal leaks and will throw some oil onto the top of hood.this is a sign of leakage.

Hopefully the r-134 fittings can be removed without damaging the r-12 fitting, sometimes those r-134 conversation fittings have loctite on the threads.if so-don't force them off ,use a heat gun to heat-up and slowly backout.

average pressure on the low side should be about 30 psi,high side about175 psi, the outside temp does make a difference the hotter it is the higher the psi. will be.

[Charles F.]

Re: Air conditioning compressor 68 L-36

Edward:

Thanks for the responses.

I've confirmed the refrigerant mix-up and learned from Classic Auto Air (Florida) that this will create a sludge due to the incompatability of the two refrigerants (R-12 and R-134), clogging the system badly. I am also told that unless all such residue is removed, the A/C will not work in the long run.

They can rebuild the POA valve, the expansion valve, the receiver/drier and my compressor to remove the sludge and set the system up for either refrigerant. I am told that they will not guarantee the compressor unless all these parts are replaced and/or rebuilt. They claim the R-134 is a better choice than the R-12.

They recommend a thorough flushing of everything else to remove the sludge.

Does their analysis, requirements and recommendations make sense ?

I don't think my current compressor (A-6 type) is "NCRS-correct". Classic Auto Air has an A-6 type for $300 but does NOT have the core for an "NCRS-correct" compressor. If mine is correct (checking) they can rebuild it.

I asked about rebuilt versus new. I was told that they rebuild to order, so that the compressors are no more than several weeks old when returned to the customer; that such compressors do not leak.

They claimed that other rebuilds are "on spec", so that the compressors can sit for months in a warehouse, allowing the oil to get away from the seals and causing the seals to dry out. When such a compressor is started, with 300 PSI in it, the oil blows by the seals and the compressor "fails". Does this make sense or am I being "marketed" ?

I plan on ordering a non-"NCRS-correct" A-6 compressor from them [so I can get the system running], but would like to find an appropriate core for rebuild as the car is otherwise numbers-matching (anally). Any ideas where ?

Sorry for so many questions and thanks.

Chuck

[Edward J.]

Re: Air conditioning compressor 68 L-36

Chuck,
Since you had to add freon to the system, first start looking for a leak somewheres,oil from the system tends to leak out and dust collects on those areas, compressor leaks at the gas seal is common and if theres a problem with that seal it will sling oil onto the top of the hood. check all the fittings for signs of leaks, back of compressor,condensor, evaporator core,sometimes alittle soap and water on the fitting works if the system is still charged.

The next thing is the replacement parts,My say is only replace what needs to be replaced, the system will need to be flushed even if you decide on r-12 or r-134 , the down side on r-134 is the cooling is not as good as r-12, and if your in traffic the pressures rise in the system with r-134 and cooling is less effective. on the C-3 corvettes its tough enough to try and cool the samll area with R12, our cars have the worst air flow of any car I can remember, and create more heat from the engine and exhaust.

If you have a local A/C and radiator shop that specializes with the older systems, and has a machine that can flush the system. and locate the leak or leaks, that might be the way to start.

If you decide to do the NCRS correct way you'll want the R-12( pretty expensive today and may have to do little leg work to maybe find about 4 LBS.) and the correct decal for the compressor.

[Larry M.]

Re: Air conditioning compressor 68 L-36

Chuck:

I would also call/check with Old Air Products in Fort Worth, Texas. www.oldairproducts.com. They are also an excellent company, and lately seem to have a better track record/reputation that Classic Auto Air in Florida. However, both are excellent companies.

You may be able to purchase a correctly rebuilt (original) core from AC Delco. The part number for the compressor only is #15-27. Other part numbers that might be applicable are #15-2141 (non superheat rebuilt compressor with clutch) or #15-2226 (non superheat new compressor with clutch).

Long Island Corvette Supply also sells a rebuilt compressor with clutch for 1963-67 cars. I think that 1968 is similar/identical, but would need to verify with a judging manual or GM parts manual. You could also call LI and inquire about the casting and part numbers.

Another source for used original AC stuff is www.thepartguy.com. I have never used him and would approach with some caution. But he has old, used AC parts available.

Larry

[Larry M.]

Re: Air conditioning compressor 68 L-36

Ed has some excellent advice, and you should follow it.

However, regarding refrigerant prices, a can of R12 is about $20 on E-bay right now. A can of R134a sells for about $9-10 at the auto parts store. Your car uses 4 cans initially, and maybe a can per year thereafter.

R12 cost has come down significantly in recent years, and you can buy it simply by signing a waiver/release or by going on-line and getting you Section 609 license. This takes about 1 to 2 hours of time, requires an open-book test, and costs about $40. Then you are set "forever" for legally buying R12 for your car.

Nothing is easy anymore........but this is not that difficult.

Larry

[Edward J.]

Re: Air conditioning compressor 68 L-36

Larry, there is some R-12 compatable stuff out there ,My last purchase of R-12 for my 72 was about 40.00 a LB. if e/bay has the real deal for 20.00 thats great.

Chuck be aware there are R-12 substatutes out there.

[Larry M.]

Re: Air conditioning compressor 68 L-36

Larry, there is some R-12 compatable stuff out there ,My last purchase of R-12 for my 72 was about 40.00 a LB. if e/bay has the real deal for 20.00 thats great.

Chuck be aware there are R-12 substatutes out there.

Ed:

30 pound cylinders of R12 are going for $400 to $600. The higher $$$ comes from the reclaiming companies that are EPA certified. The lower $$ are from us common folks selling R12 from old inventories.

Cans are a bit higher per pound, as you might expect. $25/can seens typical during the summer, but winter prices and occasional "deals"are a bit lower (like $20/can). Shipping is extra, but you don't pay tax.

I just auctioned off 4 cans of R12 for a NCRS charity (plus a lot of other parts/stuff) for $50. The bidder got a pretty good deal, and the charity made some $.

Larry

[Jim T.]

Re: Air conditioning compressor 68 L-36

Charles this may not be your problem with your 68's air conditioner. But it is something you have not mentioned in all your postings.
The expansion valve's inlet connection has a metal screen to catch debris. If your dryer's desiccant bag has ruptured, the desiccant will flow through the condensor and will be stopped by the expansion valve's metal screen.
It will not take very much desiccant in the screen to stop/restrict the flow of R12.

What I have described to you actually happened to my 1970. The local Chevrolet dealership garage did not diagnose what the real problem was when my Corvette was taken to them because the air conditioner was not working right. The technitions wanted to replace my evaporator core to fix what they thought the problem was. It was a blessing that they could not disconnect the largest connection and quit. I was out of town on business when my wife took the 70 to the dealership. If I had been home the dealership would of never seen my Corvette.
I got out my service manual when I got home and read it. First thing I did was check the expansion valve's screen. It was packed with desiccant. Installed new dryer, cleaned the expansion valve's screen, and flushed the system from the dryer connection of the condensor to the expansion valve inlet.
Had a professional shop pull vacuum and install R12 and compressor oil.This happened in 1988 and the air still works. My Corvette's GM service manual has a good picture of the expansion valve and the metal screen.

[Larry M.]

Re: Air conditioning compressor 68 L-36

The screen that Jim mentions is available from NAPA (and others) for about $3. Let me know if you need a part number.

The hard part is replacing it.....since entire system must be depressured and then re-charged.

Larry

[Jim T.]

Re: Air conditioning compressor 68 L-36

Edward:

Thanks for the responses.

I've confirmed the refrigerant mix-up and learned from Classic Auto Air (Florida) that this will create a sludge due to the incompatability of the two refrigerants (R-12 and R-134), clogging the system badly. I am also told that unless all such residue is removed, the A/C will not work in the long run.

They can rebuild the POA valve, the expansion valve, the receiver/drier and my compressor to remove the sludge and set the system up for either refrigerant. I am told that they will not guarantee the compressor unless all these parts are replaced and/or rebuilt. They claim the R-134 is a better choice than the R-12.

They recommend a thorough flushing of everything else to remove the sludge.

Does their analysis, requirements and recommendations make sense ?

I don't think my current compressor (A-6 type) is "NCRS-correct". Classic Auto Air has an A-6 type for $300 but does NOT have the core for an "NCRS-correct" compressor. If mine is correct (checking) they can rebuild it.

I asked about rebuilt versus new. I was told that they rebuild to order, so that the compressors are no more than several weeks old when returned to the customer; that such compressors do not leak.

They claimed that other rebuilds are "on spec", so that the compressors can sit for months in a warehouse, allowing the oil to get away from the seals and causing the seals to dry out. When such a compressor is started, with 300 PSI in it, the oil blows by the seals and the compressor "fails". Does this make sense or am I being "marketed" ?

I plan on ordering a non-"NCRS-correct" A-6 compressor from them [so I can get the system running], but would like to find an appropriate core for rebuild as the car is otherwise numbers-matching (anally). Any ideas where ?

Sorry for so many questions and thanks.

Chuck

Chuck I question how a compressor just installed on a car will have 300 PSI on startup.

Ref my previous post about the desiccant and the expansion valve's screen. The screen is stainless steel and sets in the expansion valve's inlet. Something that can be used to extract it is an easy-out. Easy-outs are tapered and just a light twist will extract the screen .

[Tom L.]

Re: Air conditioning compressor 68 L-36

Well, here's my 2 cents. Unless I understand you correctly, your mechanic has diasgnosed the problem with your compressor as being ineffecient in pumping capacity due to low suction pressure, 10psi. I think. Typically a symptom of an inneficcient compressor is high suction pressure, not low.

As Jim mentions, there is a possiblity that the inlet of the TXV (expansion valve) screen is clogged. This will result in low suction pressure. One way to determine if that may be a cause without dissasembling the system is to check the superheat accross the evaporator.

I'll describe what superheat is as simply as I can. First, the air that is cooled by the evaporator is cooled by the refrigerant entering the evaporator and boiling. It takes heat to boil a liquid, the heat used to boil the liquid is absorbed from the air passing over the evaporator.

Unlike water, refrigerants have a very low boling point, for R-12 and R-134a it's about 35* F, + or- a degree or two at 30 psi (a typical suctuion pressure in an auto A/C system). As the refrigerant travels through the evaporator heat is absorbed and the liquid should boil off completely before exiting the evaporator.

Superheat, you thought I'd never get there, is the heat added to the refrigerant vapor above it's boiling temperature in the evaporator. To beter understand what I mean about "heat added to the refrigerant above its boiling temperature" I'll compare it to water. Here at sea level water boils at 212*F, as long as there is water in the open pot that will never change. The only way that the water can be at a higher temperature is if it is in the form of water vapor (steam). As we know from trying to taske a radiator cap off of an overheating engine, steam is hotter than boiling water, it has been superheated. The same happens to refigerant in the evaporator.

In the evaporator we want only a little superheat, 5-10 degrees depending on system design. This means that there is boiling liquid throughout the majority of the evaporator, a good thing. If the superheat is very high, say 20 degrees, that means that the evaporator does not have boiling liquid throughout the majority of the evaporator, a bad thing that typically results in poor cooling. A symptom of this is low suction pressure.

Possible causes of this are:

Low refrigerant charge
A restricton in the liquid line such as the drier
A restriction at the TXV such as a clogged screen
A restriction in the TXV's orifice due to sludge
A defective TXV

I hope this helps you get to the root of your problem before you begin changing parts only to find what the real problem is. If your mechanic doen't know what superheat is then perhaps it's time to find one that does. There's nothing worse than chasing a problem by throwing money and parts at it. Have fun!!

[Larry M.]

Re: Air conditioning compressor 68 L-36

Charles:

Lynn Larsen has some excellent points and info. If you know the temperatures and pressures throughout your AC system you (or a good AC technician) can quickly calculate superheat and subcooling, and troubleshoot and repair the problem the first time.

Trouble is, trying to find this person is often difficult. Keep us informed on your progress. We can help. There is a lot of EXCELLENT knowledge on this forum from the members.

Larry