slant6billy
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AC Not working only on hot days
- Thread starter slant6billy
- Start date
At first glance, my first thought is you have a refrigerant leak – for the low pressure switch is keeping the A/C clutch from engaging (which, is the most likely cause, IMO). I attached a couple of pages from my '77 FSM, to aid you.
The low pressure switch will need to have the existing refrigerant removed, first. I had a friend who removed that low pressure switch on a fully charged system who got hurt bad (sent to hospital) when the switch, and tool, hit him in the face. The switches do go bad, but a leak (somewhere) is more likely.
The problem is you are working with R-12.
BudW
The low pressure switch will need to have the existing refrigerant removed, first. I had a friend who removed that low pressure switch on a fully charged system who got hurt bad (sent to hospital) when the switch, and tool, hit him in the face. The switches do go bad, but a leak (somewhere) is more likely.
The problem is you are working with R-12.
BudW
Aspen500
Well-Known Member
As Bud said, you are either low on refrigerant or the low pressure cycling switch is bad (the part on the drier). Try jumping the terminals on the cycling switch connector and see if the clutch engages and it blows cold air.
Since you hot wired the compressor and it barely cooled, you are low on refrigerant. The biggest problem will be finding a shop that still has R-12 equipment. The best way is to attach pressure gauges and look at the refrigerant pressures. You should see at least 80 psi or more with the system off. The cycling switch cuts power to the clutch at ABOUT 20-25 psi (IIRC). This is to prevent the evaporator from freezing up mainly, and also to protect the compressor if the level is low.
At any rate, your system is showing classic signs of being low or empty. When you get it charged, make sure they put dye in the system. Then any leaks can be found using a UV light and UBV goggles. Also as Bud said, do NOT take the cycling switch out unless you know the system is empty. Released refrigerant is instant frostbite, or worse if it gets in your eyes. Beware, R-12 is VERY expensive ($100/lb around here is the going rate), if a shop actually has any. We've got one 30 lb cylinder and what's in the old recovery machine and,,,,,,,,,,,,,that's all there is.
Since you hot wired the compressor and it barely cooled, you are low on refrigerant. The biggest problem will be finding a shop that still has R-12 equipment. The best way is to attach pressure gauges and look at the refrigerant pressures. You should see at least 80 psi or more with the system off. The cycling switch cuts power to the clutch at ABOUT 20-25 psi (IIRC). This is to prevent the evaporator from freezing up mainly, and also to protect the compressor if the level is low.
At any rate, your system is showing classic signs of being low or empty. When you get it charged, make sure they put dye in the system. Then any leaks can be found using a UV light and UBV goggles. Also as Bud said, do NOT take the cycling switch out unless you know the system is empty. Released refrigerant is instant frostbite, or worse if it gets in your eyes. Beware, R-12 is VERY expensive ($100/lb around here is the going rate), if a shop actually has any. We've got one 30 lb cylinder and what's in the old recovery machine and,,,,,,,,,,,,,that's all there is.
R-12 is easy to check the refrigerant level. Look at the sight glass (at the drier, very close to the low pressure switch) with car running and A/C on. It is a small clear window, about 1/4” round at the very top. If you have the compressor jumped, via jumper wire, or as you said via a suicide cable, and with engine running, you can take a flashlight and looking through the sight glass on the drier, it will be either blank or you will see bubbles.
If you have bubbles, then your level is low.
If you see nothing, then you have a good level or you are empty.
This doesn't work as well with dye in the system – but still works. Note, using the sight glass ONLY works with R-12. The other refrigerants do not work the same way.
Note: most all new driers (for our cars) are built with the sight glass present – but typically are painted over. If using a new drier for a R-12 system, just take something to scratch off the paint, but don't scratch the glass. You can then charge the system until the sight glass goes clear, then add about 1/4th to 1/2” can (or pound) additional and you are done. No gauge set or weight scale is required (but is still recommended, if you have access to one).
When they went to R-134a, they took away the ease of working on A/C systems.
Granted, working with a refrigerant station is WONDERFUL, but overall, is still a pain. The refrigerant stations, you can dial in how much to install, push a button, and go do something else – as well as recover the existing refrigerant as well.
A/C compressors are meant to be used every so often. A minimum of once every year. Best is to run the A/C a few minutes every 3ish months or so. If you don't, the front compressor seal will either leak or go bad. The odd thing is, the A/C compressor front seal are made of ceramic – which is something I think is funny. Really, something that is “rock” hard is meant to hold back pressure?? It is just not logical to me – but it does work, and it requires refrigerant oil to keep it lubricated (which IS the reason why to cycle the A/C every so often).
The good news is it is not too hard to convert our cars to R-134a (if using either the RV-2, Sanyo or C-171) compressor.
For longevity sake, the boat anchor (the RV-2 compressor) is built like a tank and is one of the very few A/C compressors made with an actual oil pump.
For fuel mileage, the Sanyo or C-171 is your choice, but neither version will give you a lifetime of service like the RV-2 will.
First, we need to find your leak. I suspect the most likely cause is the compressor front shaft seal – but could be wrong. You need to confirm you do not have other leak(s) in system before performing any repairs. To do that, you need to will need to add dye to the existing system, preferably add more R-12 to the system, then drive car while using A/C to find that leak (with a black light).
Once all of your leaks are found, then converting your existing system to R-134a is not too terribly hard to do - but is labor intensive. A new drier and all new seals/gaskets are needed. Also flush solvent (which is expensive stuff, but required) as well as new A/C service ports.
Next, flushing out all remnants/traces of the old refrigerant oil IS MANDORY. The oil used for R-12 and R-134a highly disagrees with each other (think of putting hydrogen peroxide on a body cut on how it boils up). This is where the labor and persistence takes place because you have to work hard to get all traces of oil out. If you do it correctly and thoroughly, you will only have to do it once.
I recommend removing the compressor from the car, then remove the oil pan so you have access to perform a thorough cleaning. If, by chance, your front seal is leaking, this would be a great time to fix that, as well. I do not recommend using flush inside of the compressor. I recommend using (dried/filtered) compressed air. If you use paper or cloth inside, try to use something that will not leave any lint behind.
Most of the oil (maybe 2/3rds of it) will be inside of the compressor.
Removing the evaporator core and condenser is also highly recommended to remove first to perform a proper flush. The condenser can be done in car, but the evaporator core is a hard one to clean.
R-134a
Once converted to R-134a, it will hold 31 to 32 oz.
The (new) refrigerant oil to use will be 13 oz, “PAG 100”.
Any new rubber O-rings need to be R-134a compatible. Any O-rings not touched can be left alone.
If you have a hose leaking, the new hose will need to be R-134a compatible. Any old hoses can be reused if flushed out well.
Use a drop of PAG oil on your new O-rings and gaskets.
Use of (new) metal gaskets is fine.
Some recommend getting your old compressor rebuilt or replaced - just to make sure no old oil exists. That is not a bad idea, especially if your front shaft seal is leaking - but the cost of a replacment compressor (or rebuilding) might be a bit more than one might expect (maybe). If you are considering that method, just know I would be very interested in your old RV-2 compressor
R-12
It would be best to re-use R-12, if you can find any.
Your vehicle, if using R-12, will hold 42 oz (2-5/8 pounds).
R-12 uses mineral oil (only), 13 oz.
R-12 will not require to flush the A/C system (unless you have metal contamination – which is extremely uncommon with the RV-2 compressor).
Use a drop of mineral oil on your new O-rings and gaskets.
Use of (new) metal gaskets is fine.
BudW
If you have bubbles, then your level is low.
If you see nothing, then you have a good level or you are empty.
This doesn't work as well with dye in the system – but still works. Note, using the sight glass ONLY works with R-12. The other refrigerants do not work the same way.
Note: most all new driers (for our cars) are built with the sight glass present – but typically are painted over. If using a new drier for a R-12 system, just take something to scratch off the paint, but don't scratch the glass. You can then charge the system until the sight glass goes clear, then add about 1/4th to 1/2” can (or pound) additional and you are done. No gauge set or weight scale is required (but is still recommended, if you have access to one).
When they went to R-134a, they took away the ease of working on A/C systems.
Granted, working with a refrigerant station is WONDERFUL, but overall, is still a pain. The refrigerant stations, you can dial in how much to install, push a button, and go do something else – as well as recover the existing refrigerant as well.
A/C compressors are meant to be used every so often. A minimum of once every year. Best is to run the A/C a few minutes every 3ish months or so. If you don't, the front compressor seal will either leak or go bad. The odd thing is, the A/C compressor front seal are made of ceramic – which is something I think is funny. Really, something that is “rock” hard is meant to hold back pressure?? It is just not logical to me – but it does work, and it requires refrigerant oil to keep it lubricated (which IS the reason why to cycle the A/C every so often).
The good news is it is not too hard to convert our cars to R-134a (if using either the RV-2, Sanyo or C-171) compressor.
For longevity sake, the boat anchor (the RV-2 compressor) is built like a tank and is one of the very few A/C compressors made with an actual oil pump.
For fuel mileage, the Sanyo or C-171 is your choice, but neither version will give you a lifetime of service like the RV-2 will.
First, we need to find your leak. I suspect the most likely cause is the compressor front shaft seal – but could be wrong. You need to confirm you do not have other leak(s) in system before performing any repairs. To do that, you need to will need to add dye to the existing system, preferably add more R-12 to the system, then drive car while using A/C to find that leak (with a black light).
Once all of your leaks are found, then converting your existing system to R-134a is not too terribly hard to do - but is labor intensive. A new drier and all new seals/gaskets are needed. Also flush solvent (which is expensive stuff, but required) as well as new A/C service ports.
Next, flushing out all remnants/traces of the old refrigerant oil IS MANDORY. The oil used for R-12 and R-134a highly disagrees with each other (think of putting hydrogen peroxide on a body cut on how it boils up). This is where the labor and persistence takes place because you have to work hard to get all traces of oil out. If you do it correctly and thoroughly, you will only have to do it once.
I recommend removing the compressor from the car, then remove the oil pan so you have access to perform a thorough cleaning. If, by chance, your front seal is leaking, this would be a great time to fix that, as well. I do not recommend using flush inside of the compressor. I recommend using (dried/filtered) compressed air. If you use paper or cloth inside, try to use something that will not leave any lint behind.
Most of the oil (maybe 2/3rds of it) will be inside of the compressor.
Removing the evaporator core and condenser is also highly recommended to remove first to perform a proper flush. The condenser can be done in car, but the evaporator core is a hard one to clean.
R-134a
Once converted to R-134a, it will hold 31 to 32 oz.
The (new) refrigerant oil to use will be 13 oz, “PAG 100”.
Any new rubber O-rings need to be R-134a compatible. Any O-rings not touched can be left alone.
If you have a hose leaking, the new hose will need to be R-134a compatible. Any old hoses can be reused if flushed out well.
Use a drop of PAG oil on your new O-rings and gaskets.
Use of (new) metal gaskets is fine.
Some recommend getting your old compressor rebuilt or replaced - just to make sure no old oil exists. That is not a bad idea, especially if your front shaft seal is leaking - but the cost of a replacment compressor (or rebuilding) might be a bit more than one might expect (maybe). If you are considering that method, just know I would be very interested in your old RV-2 compressor
R-12
It would be best to re-use R-12, if you can find any.
Your vehicle, if using R-12, will hold 42 oz (2-5/8 pounds).
R-12 uses mineral oil (only), 13 oz.
R-12 will not require to flush the A/C system (unless you have metal contamination – which is extremely uncommon with the RV-2 compressor).
Use a drop of mineral oil on your new O-rings and gaskets.
Use of (new) metal gaskets is fine.
BudW
Aspen500
Well-Known Member
To add to Bud's post, A/C hoses that have had mineral oil in them become barrier hoses and are fine to use with R134a and it won't seep through the hose. The sight glass will have bubbles with R134a at the correct charge level. It isn't necessary to get 100% of the mineral oil out but as much as possible should be removed.
For future service, I would highly recommend converting to R134a refrigerant. Easily available and the cost is low, as opposed to R-12. Other than getting the mineral oil out, all you really need are adapter fittings for the charge ports. It'll cool as well as R-12 did in the otherwise stock system. Also you should change the cycling switch for a trinary one that is both low and high pressure cut off, instead of only low pressure. That way if the high side pressure goes to high, it'll disengage the clutch before the relief valve opens up and blows refrigerant out. Generally, the switch opens at 400 psi, the relief valve blows at 500 psi.
On a side note, the new R1234yf refrigerant (which cannot be retrofit anyways) is ridiculously expensive. The 10 lb cylinder for our charge/recovery machine at work is $900, which I guess is about the same per pound as R-12 ($90-$100), where R134a is about $6 per pound.
For future service, I would highly recommend converting to R134a refrigerant. Easily available and the cost is low, as opposed to R-12. Other than getting the mineral oil out, all you really need are adapter fittings for the charge ports. It'll cool as well as R-12 did in the otherwise stock system. Also you should change the cycling switch for a trinary one that is both low and high pressure cut off, instead of only low pressure. That way if the high side pressure goes to high, it'll disengage the clutch before the relief valve opens up and blows refrigerant out. Generally, the switch opens at 400 psi, the relief valve blows at 500 psi.
On a side note, the new R1234yf refrigerant (which cannot be retrofit anyways) is ridiculously expensive. The 10 lb cylinder for our charge/recovery machine at work is $900, which I guess is about the same per pound as R-12 ($90-$100), where R134a is about $6 per pound.
Last edited:
slant6billy
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thanks guys.
