AC Evacuation and Charging issues
04-08-2019, 10:54 PM
#61
Chronic Tool Dropper
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The freeze switch has a capillary tub e filled with something that expands as probe temp goes up. The fluid pushes on a little brass diaphragm that works a small snap-action switch that can interrupt current flow to the compressor clutch. The system has a certain planned-failure component, in that the brass diaphragm will work-harden over time, eventually staying in the too-hot or too-cold position, and not responding to actual changes in evaporator temp.
More modern systems look at suction-side pressure, and cycle the compressor off when pressure drops low enough to allow freezing on the evaporator fins. As Griff reminds us, low circulating pressure can affect compressor lubrication. Modern systems seem to leak less refrigerant too, and are wired and plumbed for that switch. Ours aren't. If your freeze switch is acting erratic, replace it.
For testing the system and charging, jumper the switch. As you sneak up on the ideal system temps and mass balance, you'll pass through a zone of undercharge where the evaporator will get to freezing at test-conditions load, but will actually be undercharged for many other conditions.
Do everything you can to keep air out of the system when charging. From scratch it's easy since the vacuum pump can pull the air out of the hoses and manifold. If you pull the hose from the pump and connect it to the refrigerant can, the hose will fill with air. Flip the canister over so the tap or valve is on the bottom, then purge the line at the manifold end by bleeding until liquid comes out. Air in the system even a small amount, seriously affects the ability of the system to move heat around. It doesn't evaporate at the expansion valve so almost no cooling happens there. It hogs transfer capacity in the condenser, and ultimately can contribute to corrosion in the system if allowed to stay. No oxygen means no oxidation, highlighting the need to keep the system free of moisture too. Most of this is "housekeeping" and good practice taught in AC classes.
More modern systems look at suction-side pressure, and cycle the compressor off when pressure drops low enough to allow freezing on the evaporator fins. As Griff reminds us, low circulating pressure can affect compressor lubrication. Modern systems seem to leak less refrigerant too, and are wired and plumbed for that switch. Ours aren't. If your freeze switch is acting erratic, replace it.
For testing the system and charging, jumper the switch. As you sneak up on the ideal system temps and mass balance, you'll pass through a zone of undercharge where the evaporator will get to freezing at test-conditions load, but will actually be undercharged for many other conditions.
Do everything you can to keep air out of the system when charging. From scratch it's easy since the vacuum pump can pull the air out of the hoses and manifold. If you pull the hose from the pump and connect it to the refrigerant can, the hose will fill with air. Flip the canister over so the tap or valve is on the bottom, then purge the line at the manifold end by bleeding until liquid comes out. Air in the system even a small amount, seriously affects the ability of the system to move heat around. It doesn't evaporate at the expansion valve so almost no cooling happens there. It hogs transfer capacity in the condenser, and ultimately can contribute to corrosion in the system if allowed to stay. No oxygen means no oxidation, highlighting the need to keep the system free of moisture too. Most of this is "housekeeping" and good practice taught in AC classes.
04-09-2019, 06:37 AM
#63
Rennlist Member
The item Dr Bob was referring was the capillary switch- this is not a control device it is a protective device and only kicks in when necessary which should be rare unless folks use their a/cs when there is no real need.and then the thing stops the compressor from operating until it senses the temperature is a tad warmer than the set point. Unfortunately the WSM is very poor at advising set point data of the various instrumented components- that or I have been looking in the wrong places!.
Last edited by FredR; 04-09-2019 at 06:53 AM.
04-09-2019, 01:51 PM
#64
Rennlist Member
The expansion valve has nothing connected to it electrically but it does have a modulating action of some kind if someone can explain that "modus operandi".
The item Dr Bob was referring was the capillary switch- this is not a control device it is a protective device and only kicks in when necessary which should be rare unless folks use their a/cs when there is no real need.and then the thing stops the compressor from operating until it senses the temperature is a tad warmer than the set point. Unfortunately the WSM is very poor at advising set point data of the various instrumented components- that or I have been looking in the wrong places!.
The item Dr Bob was referring was the capillary switch- this is not a control device it is a protective device and only kicks in when necessary which should be rare unless folks use their a/cs when there is no real need.and then the thing stops the compressor from operating until it senses the temperature is a tad warmer than the set point. Unfortunately the WSM is very poor at advising set point data of the various instrumented components- that or I have been looking in the wrong places!.
04-09-2019, 01:57 PM
#65
Glad to see that lube circulation has finally been brought up in this discussion.One thing I have not seen mentioned yet,and if it was please excuse me as I only quickly scanned the responses from my posting yesterday,is the quality of air flow over the evap core,or simply put,lots of dirt and debris on the back side of the evap core.I learned this back in the late 80's,after a Ford E series van slaughtered me on fixing a very poor performing a/c system.Finally,I was up to replacing the evap,only to find when I removed it,the back side was covered in dirt and debris.This said,years later when I had the dash out of my 79,I opened the evap box,only to find that the evap was also covered in dirt and brown carpet fibers.What a huge difference cleaning it made to the coolness of the cabin,once the vehicle had been run for awhile..Not to the standards of my GM products,but much better.AND,the compressor ran longer before the system cycled on/off to keep the evap from freezing.
On to the 86 with dual a/c.I long ago stopped worrying about slight freon loss.I had resealed everything on that car more than once,and just chalk it up to lack of use during the nasty months,which leads to the front comp seal leaking slightly,as it looses its oil film that performs the final sealing on the old ceramic seal style front comp seals.Just easier to add a can,or,just not drive it in the hot months.My cheap GM trucks blow ice cubes in minutes,and the 944 a/c,which is nippondenso,cools really good
On to the 86 with dual a/c.I long ago stopped worrying about slight freon loss.I had resealed everything on that car more than once,and just chalk it up to lack of use during the nasty months,which leads to the front comp seal leaking slightly,as it looses its oil film that performs the final sealing on the old ceramic seal style front comp seals.Just easier to add a can,or,just not drive it in the hot months.My cheap GM trucks blow ice cubes in minutes,and the 944 a/c,which is nippondenso,cools really good
04-09-2019, 04:33 PM
#66
Fixer,
Yup. You need clean cooling fins on the evap for heat transfer.
"which leads to the front comp seal leaking slightly,as it looses its oil film that performs the final sealing on the old ceramic seal style front comp seals"
If you have a leak at the nose seal, meaning refrigerant is pushing out, its taking oil with it but you are not losing any oil film which performs a 'final sealing'; although if you let a 3 ft diameter puddle form
under the car from the leak, then you lost a lot of oil. The compressor nose seal assembly has 2 primary seals. The shaft o-ring seals the OD of the shaft, and the o-ring around the race seals
the ID of the nose bore.
Yup. You need clean cooling fins on the evap for heat transfer.
"which leads to the front comp seal leaking slightly,as it looses its oil film that performs the final sealing on the old ceramic seal style front comp seals"
If you have a leak at the nose seal, meaning refrigerant is pushing out, its taking oil with it but you are not losing any oil film which performs a 'final sealing'; although if you let a 3 ft diameter puddle form
under the car from the leak, then you lost a lot of oil. The compressor nose seal assembly has 2 primary seals. The shaft o-ring seals the OD of the shaft, and the o-ring around the race seals
the ID of the nose bore.
04-09-2019, 04:55 PM
#67
Chronic Tool Dropper
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The expansion valve is a thermo-mechanical metering valve. It allows (hopefully) liquid refrigerant into the evaporator, based on the temperature of the vapor passing out of the evaporator. More liquid going in takes more cabin heat to vaporize. The expansion valve is challenged with adjusting refrigerant flow to accommodate the wide range of operating conditions that the system sees, and they are generally very good at that if the right system pressures are maintained and there's liquid available coming in.
There are no electrical components in the expansion valve. You can see the little diaphragm on the end of the valve, responding to changes in temperature in the suction line to the compressor. If you look through the valve, you can see the needle actuated by that diaphragm as it passes back towards the pressure side of the valve. There's more to the total function of the expansion valve, but its principal duty is to adjust refrigerant liquid flow based on heat load on the evaporator.
There are no electrical components in the expansion valve. You can see the little diaphragm on the end of the valve, responding to changes in temperature in the suction line to the compressor. If you look through the valve, you can see the needle actuated by that diaphragm as it passes back towards the pressure side of the valve. There's more to the total function of the expansion valve, but its principal duty is to adjust refrigerant liquid flow based on heat load on the evaporator.
04-09-2019, 05:18 PM
#68
Three Wheelin'
Thread Starter
Paul --
Run the engine at 1500-2000 RPM and note the ambient temp, the system pressures after 5 minutes, the center-vent temp at the same time, and the temperature at the passenger's feet. Interior fan speed set at 2, slider at full-cold, and your armrest vents closed. The rear system is off, and the freeze switch is jumpered. The RH or dew point number may help. Share those numbers here please
Grab some readings and share them here. There are some system experts here that can help you find just the right balance.
Run the engine at 1500-2000 RPM and note the ambient temp, the system pressures after 5 minutes, the center-vent temp at the same time, and the temperature at the passenger's feet. Interior fan speed set at 2, slider at full-cold, and your armrest vents closed. The rear system is off, and the freeze switch is jumpered. The RH or dew point number may help. Share those numbers here please
Grab some readings and share them here. There are some system experts here that can help you find just the right balance.
certain I have proper charge, and no air or water in system, so what's next? too much oil? blockage? expansion valve? drove for a while, and dash temps are cooler at 52', and I am not terribly uncomfortable, but something is not right?
04-09-2019, 05:39 PM
#69
Chronic Tool Dropper
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Verify the vacuum system is holding correctly. Your pressures are OK but you need more condenser airflow to drop the head pressure.
--
I went through a similar discovery process a few years ago now. Same symptoms. I had a vacuum leak at the HCV diaphragm that affected the other diverters/doors. Even though the HCV was tied closed and no coolant flow through it, the leak on the vacuum side was enough to present the symptoms you see. I was quite fortunate the leak was at the most-accessible actuator in the car. I popped a golf tee into the hose and everything suddenly balanced perfectly. and ice cubes for martinis started falling out of the vents.
I was ready to replace expansion valves and front drier, as the symptoms pointed at those as possible obstructions. Glad I went through the rest of the system. I now have a spare set of expansion valves in the parts drawer.
--
I went through a similar discovery process a few years ago now. Same symptoms. I had a vacuum leak at the HCV diaphragm that affected the other diverters/doors. Even though the HCV was tied closed and no coolant flow through it, the leak on the vacuum side was enough to present the symptoms you see. I was quite fortunate the leak was at the most-accessible actuator in the car. I popped a golf tee into the hose and everything suddenly balanced perfectly. and ice cubes for martinis started falling out of the vents.
I was ready to replace expansion valves and front drier, as the symptoms pointed at those as possible obstructions. Glad I went through the rest of the system. I now have a spare set of expansion valves in the parts drawer.
04-09-2019, 05:50 PM
#70
Rennlist Member
Hi Merch,
Your pressures seem just a little high, especially the high side. This may be due to overcharge, poor condenser fan function, bad condenser function due to dirt, blockage, etc. You can try spraying cold water on the condenser and see if the pressure drops; that would point slightly toward condenser heat exchange function.
Good luck,
Dave
Your pressures seem just a little high, especially the high side. This may be due to overcharge, poor condenser fan function, bad condenser function due to dirt, blockage, etc. You can try spraying cold water on the condenser and see if the pressure drops; that would point slightly toward condenser heat exchange function.
Good luck,
Dave
04-09-2019, 06:15 PM
#72
Rennlist Member
Paul,
Have you checked the recirc flap to ensure it is fully closed? When the diaphragm starts to fail it does so by not being able to hold vacuum or as Dr Bob says, any leaking actuator can reduce the vacuum available from the passive reservoir. To check the flap you simply crawl into the passenger footwell and stick a pinky vertically through the hole in the cover to determine whether the flap is up, down or somewhere in the middle. Either way the compressor discharge pressure looks somewhat high. A blockage in the expansion valve usually sees the suction pressure drop very low and that is not the case based on your data.
Have you checked the recirc flap to ensure it is fully closed? When the diaphragm starts to fail it does so by not being able to hold vacuum or as Dr Bob says, any leaking actuator can reduce the vacuum available from the passive reservoir. To check the flap you simply crawl into the passenger footwell and stick a pinky vertically through the hole in the cover to determine whether the flap is up, down or somewhere in the middle. Either way the compressor discharge pressure looks somewhat high. A blockage in the expansion valve usually sees the suction pressure drop very low and that is not the case based on your data.
04-09-2019, 06:31 PM
#73
Three Wheelin'
Thread Starter
griff: I was so fixated on WSM pointing to 2k, I didn't pay much attention to idle, but I do remember that high side at idle was 225.
just went out for a drive, and dash temp vent readings are 37' is it possible that some running of the system created some equalization? or is my issue now becoming intermittent? suggestive of what?this might sounds insane, but my center vent temp is lower and definately feels cooler with fan at 1, 2, or 3. With fan on high, temp is 6 degrees higher. am I dreaming? I have been posting in another thread about some voltage issues with idle and fan on high: is there any way, if the fan is creating a big draw, that cooling might be compromised?
04-09-2019, 06:39 PM
#74
Three Wheelin'
Thread Starter
Hi Merch,
Your pressures seem just a little high, especially the high side. This may be due to overcharge, poor condenser fan function, bad condenser function due to dirt, blockage, etc. You can try spraying cold water on the condenser and see if the pressure drops; that would point slightly toward condenser heat exchange function.
Good luck,
Dave
Your pressures seem just a little high, especially the high side. This may be due to overcharge, poor condenser fan function, bad condenser function due to dirt, blockage, etc. You can try spraying cold water on the condenser and see if the pressure drops; that would point slightly toward condenser heat exchange function.
Good luck,
Dave
04-09-2019, 06:54 PM
#75
Rennlist Member
Hi Merch,
I would not add any more refrigerant. Believe it or not you may still be slightly overcharged. If fans are working, including front condenser fan, then I would wait for Griff to advise. Post your idle pressures if you hook up your gauges again. 37 F. vent temps are not that bad.
On a difficult case, I like to charge gradually. If your goal is 85% of R12 amount, I might charge to 70%, then evaluate temps and pressures. Then go to 75% evaluate, etc. I quit at 85% or if the temps start going up. Sounds like you are getting close, and yes high fan speed will definitely give you warmer vent temps, but may cool the car more quickly.
Good luck,
Dave
I would not add any more refrigerant. Believe it or not you may still be slightly overcharged. If fans are working, including front condenser fan, then I would wait for Griff to advise. Post your idle pressures if you hook up your gauges again. 37 F. vent temps are not that bad.
On a difficult case, I like to charge gradually. If your goal is 85% of R12 amount, I might charge to 70%, then evaluate temps and pressures. Then go to 75% evaluate, etc. I quit at 85% or if the temps start going up. Sounds like you are getting close, and yes high fan speed will definitely give you warmer vent temps, but may cool the car more quickly.
Good luck,
Dave