Automotive Air Conditioning Information Forum (Archives)

acbob on Mon September 16, 2013 11:48 AM

Year: 1966
Make: Chevy
Model: Impala
Engine Size: 396
Refrigerant Type: R134a

Newby here so sorry if issue has been addressed. I blew the high pressure hose off my condenser so I thought it would be a good time to convert to R134a. New compressor, expansion valve, POA upgrade valve, and dryer. I drained and measured the oil that was pre loaded and added an additiional 2 extra oz of PAG oil to the compressor to bring the total to GM service manual requirements (11 oz.). Flushed the system, evacuated for one hour and charged. the compressor got so hot it was smoking. One line to the evaporator was cool (not cold) and the other was so hot it couldn't be touched.

I removed the compressor and drained to oil to measure. I only got a drip. Where has the oil gone? No leaks. I now have a new compressor but I am reluctant to install it for fear of ruining that one as well. I blew out the system with hard blasts of compressed air but very little oil came out of the system.

Now I am wondering how much oil I should put back in the system and WHERE should it go?

HECAT on Mon September 16, 2013 12:02 PM

So you flushed everything being reused completely clean and dry and added the full load (you say 11 ounces) of oil?

How much R12 did the sytem call for and how much R134a did you cahrge in?

What are the system pressures when operating?

Did you upgrade or add fans to the condenser?

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FLUSHING TECHNICAL PAPER vs2.pdf 

acbob on Tue September 17, 2013 8:48 AM

The system was flushed and blown out many times with compressed air. I let the air pressure build up and then released it suddenly so a high velocity of air blew out.

The original R12 requirement was 3.75 lbs. I put in 80% of that which is 3 lbs. of R134a.

The original oil requirement was 11 oz. I put in 83% of that (according to compressor instructions) which is 9 oz.

No gauge readings that are meaningful as the overheating caused me to shut down.

I plan on putting a fan on the front of the condenser but don't have one on now. Lack of fan at this point shouldn't be causing the problem. I had two window fans blowing on high across the condenser.

mk378 on Tue September 17, 2013 10:33 AM

Try to use 100% of the specified refrigerant charge unless the high pressure gets too high. Running with a low charge will cause poor cooling and (somewhat unexpectedly) overheating of the compressor. The compressor depends on flowing refrigerant to keep cool.

Also keep your system POA valve unless the valve is actually defective and you can't find another one. It's a better system than trying to cycle on pressure with the "upgrade".

HECAT on Tue September 17, 2013 11:31 AM

Quote
Originally posted by: acbob


The original oil requirement was 11 oz. I put in 83% of that (according to compressor instructions) which is 9 oz.

I am confused by this statement. I just don't see a compressor manufacturers instructions shorting the oil. When you drain the shipping oil from a new compressor, install new parts, flush what is being reused; the system now has no oil, and requires the full amount.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

wptski on Tue September 17, 2013 2:03 PM

Quote
Originally posted by: mk378
Try to use 100% of the specified refrigerant charge unless the high pressure gets too high. Running with a low charge will cause poor cooling and (somewhat unexpectedly) overheating of the compressor. The compressor depends on flowing refrigerant to keep cool.

Also keep your system POA valve unless the valve is actually defective and you can't find another one. It's a better system than trying to cycle on pressure with the "upgrade".
I've read here to charge 90%, 95% and now 100% but you saying, unless the high pressure side gets too high. What's too high?

acbob on Wed September 18, 2013 8:31 AM

The GM service manual states oil capacity to be 11 oz. The compressor comes with 7.5 oz. with instructions that capacity should be 17%-20% of R12 OEM requirements when using R134a and to add additional oil as necessary for your particular system. Thus 9 oz. total required.

HECAT on Wed September 18, 2013 12:32 PM

Quote
Originally posted by: acbob
The GM service manual states oil capacity to be 11 oz. The compressor comes with 7.5 oz. with instructions that capacity should be 17%-20% of R12 OEM requirements when using R134a and to add additional oil as necessary for your particular system. Thus 9 oz. total required.

OK, so you are probably replacing an old A-6 (I assume) with a more modern compressor and the total oil charge is less. No oil in the compressor when removed usually means it is all pooled in the evap and not moving back to the compressor to provide adequate lubrication (thus it gets hot). Air will just blow over this pool of oil. This usually occurs when there is not enough refrigerant to move the proper oil charge, or there is not enough oil for the proper refrigerant charge to move.

With the new compressor I would start again with a flush and good drying so the system has no oil, drain the shipping oil from the new compressor, add the full 11 ounces of oil this time. Where, is not so important, just be sure to rotate the compressor before startup if you put a lot in it.

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HECAT: www.hecatinc.com You support the Forum when you consider www.ackits.com for your a/c parts.

FLUSHING TECHNICAL PAPER vs2.pdf 

acbob on Fri September 20, 2013 2:34 PM

I am making SOME progress. With less refrigerant in the system I ran the car at fast idle, AC on max, two window fans blowing across the condenser and the compressor did not overheat to the point of smoking but the air coming from the vents is only slightly cool (not cold). It's a typical hot and humid day here in South Florida. Temp: 87 Humidity: Is only 53% which is low for Florida summer afternoon.

The compressor cycles on/off in one second intervals. That seems like a lot of cycling. I might take the suggestion of MK378 and put my old POA valve back in. That's another $50 of refrigerant as well as breaking the lines again, vacuuming out, new dryer, etc.

The readings are as follows:

Low side compressor "on": 45 psi
Low side compressor "off"" 25 psi

High side compressor "on": 175 psi
High side compressor "off": 150 psi

Again, this is one second compressor on/off cycle.

I'm encouraged to add a little bit more refrigerant but concerned the high pressures will skyrocket again.

mk378 on Mon September 23, 2013 9:39 AM

You need a lot more refrigerant. Running a conversion with the stock tube and fin condenser might end up with the high side pushing 300.

Also having the hose blow off in the first place suggests there could be a condenser airflow issue all along.

A high cutout switch (they trigger at about 450 psi) should be fitted to cars like yours, to help avoid blowing something out if the condenser overheats.

Edited: Mon September 23, 2013 at 12:11 PM by mk378

acbob on Wed September 25, 2013 2:35 PM

Thanks for the reply. I'm in the process of buying an electric fan for the front of the condenser. It will pass 2250 CFM. I hope this helps the condenser temps and pressures. After installation I will run the car to let things normalize followed by adding more refrigerant and watching the pressures. I assume a switch and compressor that cycles every second is not correct.

iceman2555 on Wed September 25, 2013 6:02 PM

It is assumed that the compressor was an A6...is this so? Is this an GM OE type A6 or an aftermarket replacement? If this is a OE type A6, then the system is drastically undercharged with lubricant. Why would one remove oil from a compressor for a retro fit. This makes no sense at all. Also it was stated that the compressor was 'pre loaded' with lubricant...what type...how much was in the compressor...was it drained and measured....and then 2 oz of lubricant was added to the compressor. There are serious issues with this assumption that the compressor was truly precharged with lubricant. So the decal or some notification indicated such....however, how do you know for sure this was valid. What company supplied this compressor. Never trust a label for how much oil is in the unit...always drain and refill. Also it appears that the type is also an unknown. Normally compressors are shipped with full system oil charges. There are a few examples....the V5/7 series, but most others are shipped fully charged. A system should never be short charged with lubricant.
Attempting to flush a system with air is ridiculous. Air is simply not capable of removing residual lubricants or debris from a system. It requires a liquid flush to remove these chemicals. Blowing air does nothing to clean a system.
A discharge line that indicates sufficient heat to result in these type temps tend to lead to a restriction in the condenser. Lack of adequate cooling (fans etc) could raise temps...but it appears that this may not be the only factor.
A hose was 'blown' off the condenser...the inlet hose or the outlet hose....where these hoses maintained with worm clamps or a factory type clamp. Adding additional fans for the condenser is a good method to increase condenser cooling...but why not also replace the condenser with one of the more modern 6mm Pics. This would drastically enhance the performance of your system...esp with 134a.
Pressures are almost meaningless with a retro fit. Adding a refrigerant into a system that was never designed to function with this chemical displaces what could be considered 'normal' operational pressures. Short charging a system is guaranteed to result in a compressor failure....even with an OE A6. They will pump dry also.
What part of SFL do you live?
A suggestion would be to purchase a good AC flush. Completely clean the system..insure all residual lubricants and possible debris is removed. Install a new rec/drier/filter...insure that it is plumbed correctly. The inlet and outlet on this drier are the same thread size...and could have the incorrect refrigerant flow path. This could result in some of the problems being encountered....high pressure...hose 'blowing'.
Insure the compressor is properly charged with the correct lubricant (need to know what type compressor is being used) and then sufficient lubricant is added to the system. Factory oil charge was 10-11 oz for the compressor only. Not a fan of cycling an R4...it was never designed for this....however, the OE POA may not function with 134a without modifications. There is a post on this site for how to modify the POA valve for 134a.
The refrigerant recharge of 90-95 % should be close for the system.
Good luck.
Send site sponsor your contact info and we can arrange telephonic conversations if you would like. East coast of South FL here

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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

mk378 on Wed September 25, 2013 9:08 PM

If your compressor is indeed an A6, it will have an oil plug in the side of the case and you need to add and remove the oil there rather than through the lines. Also if you ordered a "new" compressor for a 1966 car, it likely came filled with mineral oil because they're expecting you to be using R-12.

Edited: Wed September 25, 2013 at 9:14 PM by mk378

acbob on Thu September 26, 2013 5:42 PM

I can't seem to delete this blank post.

Edited: Thu September 26, 2013 at 6:04 PM by acbob

acbob on Thu September 26, 2013 5:45 PM

The new compressor I bought is an A6 direct bolt on designed for R134a and has PAG 46 oil in it. I drained the oil out to measure before install. Label states it has 7.48 oz. PAG 46. I drained out 5.5 oz. I then refilled it with the 5.5 I got out and an additional 2 oz. The new dryer is marked "in" and "out". The "in" faces the condenser. The barrier hose that blew is the one that goes from the condenser to the muffler. It has since been successfully reattached and secured. The evaporator and condenser are clean and flowing correctly. All parts of the system have been replaced except the muffler. Additionally the system has been flushed, evacuated, tested for leaks and recharged. I even took it to a local AC shop. All they did was recover my refrigerant, vacuum the system down and put the refrigerant back in. The car was returned to me the same as when I brought it to them. They charged my $100 for doing nothing to help. So much for that professional shop.

The only part in the system that isn't replaced now is the muffler. Do mufflers go bad? A new one is $100.

Thanks or all the help for everyone. I am learning a lot. Pretty much everything suggested has been done. I think my only hope is to replace the muffler, put on the electric fan and play with the amount of charge going into the system. I like in SW Florida a bit north of Ft. Myers.

Edited: Thu September 26, 2013 at 6:02 PM by acbob

iceman2555 on Thu September 26, 2013 7:04 PM

A quick test for the muffler would be to simply measure the inlet and outlet tubes. The temps should be almost the same. A temp drop would indicate a possible restriction. Trying to remember is this unit had a baffle screen or was simply a open tube inside. Will research this a bit more. Also test the rec/drier the same way. Temps should be very close. A temp drop could indicate a reverse flow. Have seen the 'indicators' placed incorrect in the past. Just insurance.
The compressor described is typically a Denso clone. 10 cylinders, swash plate, fixed displacement. PAG 46 is the correct charge rate. Check OE spec's and match this amount. 7 oz appears to be a bit low. This compressor normally would require app 2-2.5 oz for lubrication. The remainder would be displaced thru out the system. This compressor definitely requires the correct charge rate to maintain lubricant flow.
The posted pressures indicate two concerns. One a serious undercharge. The high side should be much higher....perhaps around 300 psi. The low side would be acceptable....but the fact that the two pressures do not equalize rapidly is a bit disconcerting. This is typical of a restriction....back to the rec/drier and perhaps muffler.....test the condenser for flow....a temp drop of 25-30 degrees should be obtainable with a proper operating fan clutch/engine cooling.
Still think a system flush would be in order...to insure that the correct amount of lubricant is in the system. Blowing with air is not a good method to insure lubricant removal. Excessive oil will result in a loss of cooling.
Check the rec/drier.....the 'can' should be the same temp...top to bottom. If the bottom is cooler....has condensation....there is too much oil in the can or there is a flow problem.
Other side of the state....a bit north of WPB.
Good luck....


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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson

acbob on Fri September 27, 2013 9:35 AM

The system has been flushed more than once and the dryer is new each time I opened the system. I'll try the temp measurements. Right now the muffler as indicated by my infrared temp gauge is reading 264 deg F. It's too hot to touch. I haven't checked the hoses at either end but will do that.

iceman2555 on Fri September 27, 2013 11:30 AM

First, I never trust infrared or laser type guns. Test have found them to be very inaccurate. One test with a very well represented gun indicated a variation of 90+ degrees. A good digital temperature tester such as a UEI DT222 and Surface Contact Temperature Probes are necessary to properly evaluate AC systems. A test of this temperature would not be valid. This would indicate internal pressures exceeding 900 psi.

Even considering that the line or muffler is too hot to touch does indicate a serious flow problem. Typically at about 113-115 F. surface temperature one will not wish to touch an object. Pain stimulators at very active at this point. If this is the temperature at the high side service port, this would equate to the indicated pressures in a previous post. If this temperature is of the muffler located in the discharge port...then the restriction is in the muffler, condenser, or the flow of the receiver drier. It could even be something as simple as a bad AC hose with a internal break and acting as a 'flapper valve'. The system must be evaluated to locate this restriction...before it will function.

It should be fairly simple to locate the restriction. Simply operate the system and begin temperature testing at the discharge port of the compressor. (compressor outlet to condenser). Simply follow refrigerant flow direction.... testing each component until a drastic temperature change is noted. Once the temperature drops drastically this is the restriction.

The introduction of air (or other gases) into a part as a test for flow is not a valid test. This simply means that exactly one of the tubes is open or partially flowing. It is not a true test of the flow of that particular part.

Stated the system had been flushed multiple times...what chemical was utilized and how was it removed from the system? What mechanical method was used to flush the system....blow thru cans....AC flush container/liquid flush and air....etc.

Has it ever been determined exactly how much lubricant is in the system? The post indicted various amounts added at various times. Just curious. Excessive lubricant can be a restriction also.

There is one variable that can not be allowed....the system must be fully and properly charged to adequately test the system. Variations of charge levels affect pressures and temperatures drastically. Normally a good starting point for a retro fit would be 90% of the factory R12 charge rate. If using a manifold hose and cans allow for 3-4 oz for pre filling the manifold and hoses.

Just re read part of the post........it was stated that the evaporator was cool to touch on one side and the outlet was 'too hot' to touch. What area was too hot to touch....if this was the inlet side before the TXV, this is normal. The outlet of the TXV and inlet of the evaporator should be cold. The outlet of the evaporator should be almost the same temperature as the inlet...a few degrees warmer is good. (If measured with a good temperature tester). Touching by hand would be almost the same temp.

Also what TXV do you have for your system. There were two units utilized, one for an external equalization (two tubes) and an internal equalization valve (one tube with a sensor bulb or curled area at the tip). How was the sensor attached to the evaporator outlet. It such be attached to a clean surface utilizing a mechanical attachment device (worm clamp works) and insulated (black gummy tape) for proper operation.

Take some photos of our system and post them. Let's see what we may see.

Good luck.







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The strongest reason for the people to retain the right to keep and bear arms is, as a last resort, to protect themselves against tyranny in government.
Thomas Jefferson



Edited: Fri September 27, 2013 at 11:33 AM by iceman2555