Automotive Air Conditioning Information Forum (Archives)

AndrewP on Sat January 10, 2015 7:19 AM

Year: 71
Make: Jensen
Model: Interceptor
Engine Size: 383cc
Refrigerant Type: R290 - R600a
Ambient Temp: 25C
Country of Origin: Australia

All,

Firstly, a brief intro.

Here in Australia, you are not allowed to do your own car A/C. Hence my situation.

I have a 1971 Jensen Interceptor which has a Mopar 383 motor.
It originally came with a York 210 compressor and R12 refrigerant when new, but mine had been retro-fitted with R134a at some point in its life before I purchased it.

Once of the many jobs I wanted to do when I got it was to get the A/C working again, so i began to research what i could do by myself to save some $$.

I ended up re-conditioning the compressor (new seals, gaskets etc), changing the old hoses over, new multi-flow condenser, new TX valve, new receiver/driver with med + hi pressure switches to switch on the new 12" fan in front of the condenser and the hi to cut out if something goes wrong.

I also at the time decided on trying some of the available R134a alternatives (namely refrigerant grade propane/Butane mixes) as I had heard good things with regards to retro-fitting with older systems.

I originally went through the motions (vac'd the system down, check it held vacuum etc) before re-gassing to firstly a weight converted from the R12 capacity, and then secondly using the PT info for the gas.

Just for reference, at zero C, vapor PSI is 38 (261 kpa) for the gas (according the MSDS its ~40-60% R290 and ~40-60% R600a)

I managed to achieve vent temps of around 6-10 degrees depending on the road and conditions (if I had been driving a while the temps got right down to 5 or 6, but in traffic it shot up to 16-20)

The issue I had was the York sapped way too much power from the engine and had poor performance at low RPM (idling sitting in traffic) so I began to look at the Sanden conversions.

Ive recently completed the fit and went through the same process as before in vac'ing the system down, making sure it held vacuum and regassing.

The issue I need assistance with is:

No matter what amount of gas (either weight or pressure) I cannot get the vent temps down below 25 degrees. The low side pressure is as per the PT chart for 0 degrees C (38 PSI) and the high is around the 250PSI +/- 25 PSI. Ambient was around the 28-30 degrees (83 F).

I dont think I have a blocked or restricted evaporator due to the temps I had previously seen with the old York compressor. The new Sanden seems to be healthy, good pressures and no noise, everything is new in the system apart from the evaporator (which is buried behind the dash) but I have used a endoscope and it looks OK, with no tracer dye or major signs of damage.

So what next? Im close to chucking in the DIY part and getting a A/C place to fix it, but for my own sanity Id like to find out why Im unable to achieve better results given the expense (multi-flow condensor + new Sanden 508) to date.

The only things I can think of are the TX valve is wrong (wrong values, wrong tonnage etc) as I went for a common R134a TX Valve as the old original one had no markings on it or the evaporator is somehow blocked (airflow).
The sight glass on the receiver drier is just 'on the bubble' so the TX valve seems to be getting constant flow of refrigerant.

How would I be able to tell if the TX valve is under or over sized? Is there a way to determine what the tonnage and superheat values I should be looking for?

Anyway..Id appreciate any help as locally this type of thing is difficult to get info on as the standard response is 'take it to an A/C place'. Id like to find out what the fault is before throwing more $$ at it.

Thanks in advance if you can assist.

mk378 on Sat January 10, 2015 2:11 PM

Is the low side line getting cold? You may have cold air leaving the evaporator but getting reheated in the heater core before it reaches the vents.

Is there a POA or similar pressure control valve in the suction line? Those valves go bad.

The TXV sensor bulb needs to be in good thermal contact with the side of the pipe coming out of the evaporator and insulated from external heat.

HC refrigerant doesn't work real well in TXV systems due to different pressure-temperature than R12 or 134a. Those two (C)FC refrigerants are similar enough that the same TXV can be used for either. I don't think there are any TXV's calibrated for HC.

Edited: Sat January 10, 2015 at 2:13 PM by mk378

Dougflas on Sun January 11, 2015 4:48 AM

Quote
Originally posted by: mk378
Is the low side line getting cold? You may have cold air leaving the evaporator but getting reheated in the heater core before it reaches the vents.



Is there a POA or similar pressure control valve in the suction line? Those valves go bad.



The TXV sensor bulb needs to be in good thermal contact with the side of the pipe coming out of the evaporator and insulated from external heat.



HC refrigerant doesn't work real well in TXV systems due to different pressure-temperature than R12 or 134a. Those two (C)FC refrigerants are similar enough that the same TXV can be used for either. I don't think there are any TXV's calibrated for HC.

If it's any help,Mopar systems of 1971 used TXV's for metering. The pick up sensor/bulb fit into a pocket of the suction line. These systems also used the RV2 compressor with a EPR valve in it which also caused problems. You changed the compressor so you wi need to modify the system to control the evaporator temps to prevent freeze ups.

AndrewP on Sun January 11, 2015 7:40 AM

Hi MK378 & Doug

Thanks for the replies guys..makes alot of sense (after the red mist had cleared after nearly a whole day getting no-where with this!).

Quote
Originally posted by: mk378
Is the low side line getting cold? You may have cold air leaving the evaporator but getting reheated in the heater core before it reaches the vents.

Its getting cold, but not sweating like it did with the York. There is a little heat soak in the air flow system happening. Its not a huge issue as the heat soak is minimal, but I need to lag the airbox a bit better to reduce it further. Its not sufficient to negate the chilled air from the evaporator however (but Im sure it doesnt help).

Quote
Originally posted by: mk378
Is there a POA or similar pressure control valve in the suction line? Those valves go bad.

Nope, no POA in the setup. Just a TXV

Quote
Originally posted by: mk378
The TXV sensor bulb needs to be in good thermal contact with the side of the pipe coming out of the evaporator and insulated from external heat.

Ive strapped the sensor bulb to the outlet of the evaporator using a few cable ties. I may look at improving the design as Doug has mentioned below, there is supposed to be a clip or pocket to pop the bulb into (soldered onto the pipework) but mine is missing this. Its insulated as best as it can be though.

Quote
Originally posted by: mk378
HC refrigerant doesn't work real well in TXV systems due to different pressure-temperature than R12 or 134a. Those two (C)FC refrigerants are similar enough that the same TXV can be used for either. I don't think there are any TXV's calibrated for HC.

This is where, If I were a betting man I think the issue is. Given the relative masses for the HC gas Im trying to use (again, from the MSDS) are almost 35-40% of R134a, I think the TXV is the problem. I`ll see if I can find a HC TXV, but I have drawn a blank at the moment.
Anyone know of any other gases in either commercial or industrial systems that have the same TXV setup?

Doug, the later Jensens (with the 440) had the RV2 type of compressors in. Ive no idea if the EPR valves were a problem, but many owners are changing the RV2 compressors out due to lack of spares anywhere other than the US. Finding parts and then the postage makes it un-economical to repair vs. the Sanden route.

Thanks guys anyway...I`ll see if I cant find a closer TXV (a gas with closer properties to the HC than R134a) that might work.
If nothing else, I can at least get a local AC place to regas the system to weight (the original used 2lbs of R12, so they can do the maths) with R134a. At least Ive saved a few $$ by replacing all the old hoses, and doing the replacement myself.

Cheers


Edited: Sun January 11, 2015 at 7:44 AM by AndrewP

bohica2xo on Tue January 13, 2015 2:04 AM

It is not the TXV.

You changed out a 10.3 CID compressor for an 8 CID unit. You gave up 20% of your capacity.

A 383 has plenty of power to spin the York compressor. Perhaps you need to look at the state of tune on that 383. Ignition timing at curb idle of 8 to 10 degrees BTDC really helps. Set the 700 rpm curb idle with the headlights & A/C ON. Set the timing with the vacuum advance disconnected from the distributor & plug the line while it is off.

I don't see any information on engine RPM during testing, but you need to test at 1800 engine rpm for the full picture. Run @ 1800 for two minutes, doors open & cabin fan on highest speed. Record the pressures & vent temps while @ 1800 rpm. Post them here

HC blends can be all over the place for percentages. I have used them, and would recommend letting a can sit overnight next to a good thermometer - then checking the pressure to see what you have. I run a large chiller on straight R290, and it works well.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

AndrewP on Wed January 14, 2015 9:45 AM

Hi Bohica2xo,

Cheers for the response.

First the easy bit. All the numbers Ive been quoting and recording have been @ 1750 RPM. I read somewhere its the nearest to driving RPM and a good compromise. Fan has been on full and air has been on re-circulate with the doors closed.

The 383 certainly has enough power to spin the 210. Due to the lousy fuel we get here, Im running at around 16 BTDC to stop the motor pinking. Yep..I know.. Any more and it clatters when you give it some.

Now the tricky bit. (lots of questions to follow !) I was aware that the Sanden had less a pumping capacity in as far as cc (or CID), but as it is a squash plate design, more efficient, plus Ive changed from a serpentine to multi-flow condenser therefore in real world it balances out in as far as pumping capacity and thermal dynamics. Am I wrong in this assumption?
The quantity of refrigerant in the system shouldn't change either should it? My limited knowledge is that the TXV should be fed with compressed (liquid), cooled refrigerant, and then it does its thing into the evaporator to cool the air passing over the coil down.
If the TXV is assuming its controlling R134a rather than the HC mix @ 2/3rds the mass, my assumption was that the TXV would be over-feeding the evaporator and therefore flooding it (meaning poor performance).
Again..correct me if Im wrong as Im probably making some big assumptions on my limited knowledge.

Im not able to do any more testing on it at the moment as Ive now removed the evaporator to clean, pressure test, and flush it. I had it in my head that it could also have been a blockage/air flow issue so to eliminate that Im doing this as a last job to do (as after this..every part of the system is either new or cleaned and tested).

When its back together again, I`ll have one last go and gas it up and see what results I get.

As a final question, what sort of pressures (link to the PT chart of the gas below) should I be looking for at the suction and discharge side?
Ive been aiming (gassing) the system for around 0 C which equates to 38PSI vapour.

Im worried that most info for R134a seems to state around 18 PSI and the HC gas is supposed to run LOWER pressures!

PT chart is here..appreciate any pointers you can give me.

http://www.oz-chill.com/wp-content/uploads/2013/08/Pressure_Temp-Chart-OZ-30.pdf\

Cheers



Edited: Wed January 14, 2015 at 9:49 AM by AndrewP

mk378 on Wed January 14, 2015 11:14 PM

Mass flow is compressor displacement x compressor rpm x refrigerant gas density (at suction port pressure and temperature conditions). Condenser performance isn't directly a factor. The low density and (I think) low heat of vaporization of HC compared to 134a would prefer a large compressor displacement. If you're going to keep the Sanden compressor, look at pulley sizes and make sure the compressor rpm is as high as possible. The setup should be that the engine and the compressor will reach their respective redline rpm at the same time.

Edited: Wed January 14, 2015 at 11:17 PM by mk378

bohica2xo on Fri January 16, 2015 1:31 AM

Sorry to hear about the crummy gas.

The compressor displacement reduction is a flat 20% loss. Increasing mechanical efficiency of the driving mechanics does not produce more flow, just consumes less power.

Increasing the shaft speed of the 508 by 20% over the York would work - but it is unlikely that the drive pulleys required are available.

The TXV is not sensitive to mass flow, it is a simple feedback unit with a very broad range. R12, R134, and R290 all act the same way through the same valve. AMA did extensive testing of HC's against 134a & R12 in a system with excellent data acquisition. No need to change the TXV. You may need to change the LPCO pressure, but that comes later...

Your pressures are too high. Several things could be causing this, but for starters I would say you are overcharged. This is very easy to do with HC's

Two other things that will drive up pressures are too much oil in the system, and poor condensor airflow.
A worn out fan clutch is the number one cause of high head pressures in cars of that vintage. With 45c ambient here in the desert a tired fan clutch will still move enough air to prevent overheating - but the head pressures will climb by 60% or more.

Too much oil raises pressures, and reduces cooling. The York has a sump, and circulates very little oil. The Sanden circulates the entire oil charge with the refrigerant. What quantity of oil do you have in the system currently?

Because of the nature of HC refrigerants, you will need to start over with a fresh charge. Let's figure out the oil business before you go that far.






-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.

AndrewP on Sun January 18, 2015 8:14 AM

Hi guys,

Thanks so much for the replies. Its giving me a little more confidence that what I have 'should' work.

I re-fitted the evaporator yesterday but its not all back together yet. I managed to overtighten a fitting and stripped the thread on an adapter so I have to see if I can order one locally here (a #10 to #10 female adapter) before I can give it a whirl.

The AC fan is a 12" modern electric fan that I have running when the A/C is turned on. It sits in front of the condenser as a pusher. I assume you mean a viscous fan driven off the motor (water pump normally I think) when you say clutch fan? If so, again, the Jensens normally have twin 10" electric fans, but Im using a electric 16" puller (runs around 3000 CFM) and is either thermo controlled or can be overridden in the cabin via a switch.

As you have, our ambient temps at the moment are up into the high 30's. Jensens are not renowned for running cool unfortunately so when I do a regas in the garage, I tend to turn the engine fan on straight away and place a few workshop fans in front of the car to try to keep the engine temp down.

As for the oil. Im using RL100S which is a Polyol Ester oil.

Given that the condensor was new, lines and evaporator had all been flushed out, new compressor, new TXV and new drier I added the Sanden recommended 130cc of oil to the compressor crankcase before I started using it. I figured there would be little to no oil in the system to begin with.

I did add another 100cc of oil after about the 3rd gas and discharge (as I was trying to get the vent temps down) as I noticed a fair bit of oil in the vacuum pump being pulled from the system every time I placed it under vacuum.

I dont think it has too much oil in it, but I admit I dont really know. Ive read that it can handle as much as ~ 200cc but I wouldnt want to push my luck.

Given the system has again been discharged (as Ive now removed the evaporator and cleaned it out as well as flushed again), and I`ll be vac'ing the system down again....how much oil (if any) should I add this time round?

So..assuming I have (or dont have) enough oil, Id say the only one left would be overcharging the system.

So..given the system originally has a capacity of 2lbs (907g) of R12 and R12 has a molecular mass of 120.91

The mix of the HC im using is approx 50:50 of R290 and R600a which total mass is ~51

This makes it around 42% of the R12 mass....so 42% of 907 is 380g of the HC gas

Ive been starting at around 200g of gas and charging up from there watching the pressures as I go.

Is this a good place to start..am I going about this the wrong way (charging by converted weight?)

Thanks once again for assisting. Im going to give it one last go when I can get the adapter sorted with the HC gas and plot the low and hi side pressures vs. weight so I can share the numbers with you. Fingers crossed it will all work this time round!

Cheers

Edited: Sun January 18, 2015 at 9:08 AM by AndrewP

bohica2xo on Sat January 24, 2015 2:04 AM

Oil is not normally removed by a vacuum pump. It stays in the system. What sort of vacuum pump are you using?

I would not add any more oil, you had enough before you added the extra 100 cc's.

It is very easy to overcharge with HC blends. The problem is the R600. At 35f, R600 is only 1.3 psi While R290 @ 35f is 57psi. Toss that calculator out the window.

16 to 18 psi on the low side is very common with HC blends.

Charging by vent temperature seems to be the best answer. Add very small quantities after the low side crosses 10 to 12 psi, and let the system stabilize for a minute after each change. Keep checking the thermometer in the vent. Obviously you want the lowest vent temperature.

-------------------------
"Among the many misdeeds of the British rule in India, history will look upon the act of depriving a whole nation of arms, as the blackest."
~ Mahatma Gandhi, Gandhi, An Autobiography, M. K. Gandhi, page 446.