AC compressor question.
09-15-2015, 08:16 PM
#46
Rennlist Member
Thanks Charlie. My point was that OAT is the lowest condenser ambient temp you can get. If there is low air flow, due to engine driven fans at low RPM's, then the condenser temp will be well above OAT. Best proof is to drive the same car at highway speeds and watch the vent temps come down. If you want to charge by P & T, you need augmented air flow over the condenser to come to a realistic conclusion.
Please remember, you know 10,000 times more about this stuff, so if I said something stupid, please explain.
Thanks,
Dave
Please remember, you know 10,000 times more about this stuff, so if I said something stupid, please explain.
Thanks,
Dave
09-16-2015, 09:17 AM
#47
Dave,
If I sound (read) like I'm arguing any post it is simply my 3 sense.
If I misread any post, I'm probably stuck in forward gear; some old
habits are comfortable at this age.
I agree, or say I can confirm, your point that low air flow will increase system pressures. And, variations in designs for air flow for the condenser, such a mechanical fan plus aux electrical fan a turn on point, or electrical fans with variable speeds to set points affect air flow and system pressures.
And, driving the car and observing vent temps or old school spraying water on a condenser can be a test.
But... there is a relationship between refrigerant system pressures and temperatures and it is used to help you diagnose system issues, its simply "P&T". If you use that concept or tool you can quickly diagnose system problems.
Hence, I'm not pointing at any one system component firmly at this moment, I just wanna know what the P&T is when the problem arises.
By the way, not to get too far off the thread, I see you have some boost on your car. On a typical Shark (I know there are variations in the engines over the years), what is the max boost you can "safely" (meaning things won't fall apart) apply before you have to ponder mechanical changes (fuel and ignition management is a given).
If I sound (read) like I'm arguing any post it is simply my 3 sense.
If I misread any post, I'm probably stuck in forward gear; some old
habits are comfortable at this age.
I agree, or say I can confirm, your point that low air flow will increase system pressures. And, variations in designs for air flow for the condenser, such a mechanical fan plus aux electrical fan a turn on point, or electrical fans with variable speeds to set points affect air flow and system pressures.
And, driving the car and observing vent temps or old school spraying water on a condenser can be a test.
But... there is a relationship between refrigerant system pressures and temperatures and it is used to help you diagnose system issues, its simply "P&T". If you use that concept or tool you can quickly diagnose system problems.
Hence, I'm not pointing at any one system component firmly at this moment, I just wanna know what the P&T is when the problem arises.
By the way, not to get too far off the thread, I see you have some boost on your car. On a typical Shark (I know there are variations in the engines over the years), what is the max boost you can "safely" (meaning things won't fall apart) apply before you have to ponder mechanical changes (fuel and ignition management is a given).
09-16-2015, 09:58 AM
#48
Rennlist Member
Hi Charlie. That's a great question about boost limitations. My system is limited to about 9 PSI, so I have never tried to explore the outer limits. I think there are guys running 30 PSI with stock mechanicals, but they are rare and who knows about drive train durability at that boost.
Take care, and I look forward to seeing the pressure readings here.
Dave
Take care, and I look forward to seeing the pressure readings here.
Dave
09-17-2015, 05:14 PM
#49
Thread Starter
AC compressor question.
Alright! I picked up the gauge set today (tanks again Rob) and I will get the numbers this weekend. The wife will be in Montgomery AL for training starting Sunday for 5 weeks. So getting the last of the fam time done before Sunday. Sunday is also going to be in the 90's, so should be a better test I would think.
09-20-2015, 06:02 PM
#50
Thread Starter
UPDATE
here are the numbers.
seems to cycle at 375psi hight side... rev the engine, the compressor will cycle for a few, then stabilize..... held it at 2300 ish rpm, cycled on an off
maybe my high side switch is bad..... 375 seems a little low.
here are the numbers.
seems to cycle at 375psi hight side... rev the engine, the compressor will cycle for a few, then stabilize..... held it at 2300 ish rpm, cycled on an off
maybe my high side switch is bad..... 375 seems a little low.
09-20-2015, 06:22 PM
#51
Rennlist Member
Dave
09-20-2015, 09:33 PM
#53
High side is too high for the ambient.
Low side is a tad high relative to above.
Assuming your condenser fan 'function' is what it should be in terms of air flow, and the condenser fan was operating between 1:27 and 1:40 time, and you have the correct weight of R134a refrigerant in the system (between 80-90% of the original R12 amount), I'd suggest you might have air in the system. Simply pulling a vacuum down to 29-30 inHg does not insure removal of all ambient gases, and depending upon your method/procedure of introducing refrigerant into the system.. you can have 'air' in there which raises the high side pressure above normal.
Again, depends upon whether your front condenser fan was running and the design is correct.
If the condenser fans where not operating during the test time noted then turn them on and try it again.
Low side is a tad high relative to above.
Assuming your condenser fan 'function' is what it should be in terms of air flow, and the condenser fan was operating between 1:27 and 1:40 time, and you have the correct weight of R134a refrigerant in the system (between 80-90% of the original R12 amount), I'd suggest you might have air in the system. Simply pulling a vacuum down to 29-30 inHg does not insure removal of all ambient gases, and depending upon your method/procedure of introducing refrigerant into the system.. you can have 'air' in there which raises the high side pressure above normal.
Again, depends upon whether your front condenser fan was running and the design is correct.
If the condenser fans where not operating during the test time noted then turn them on and try it again.
09-20-2015, 09:42 PM
#54
Thread Starter
AC compressor question.
Fan was on and moving air. Stock early fan. It's a howler. System was drawn down for a few hours and help vac for a day.....
Thinking of pulling it down and trying again. Maybe we some how over charged it.
Thinking of pulling it down and trying again. Maybe we some how over charged it.
09-21-2015, 11:13 AM
#55
Electron Wrangler
Lifetime Rennlist
Member
Lifetime Rennlist
Member
Did spritzing the condenser change anything for the cycling? - easy way to see if there is sufficient cooling going on.
So do you still have the single large pusher on the condenser? I had thought you had gone with a new dual puller set-up?
Alan
So do you still have the single large pusher on the condenser? I had thought you had gone with a new dual puller set-up?
Alan
09-21-2015, 11:36 AM
#56
Thread Starter
i have the dingle large pusher, then, i have Han's fan set up for the radiator. did not try the spritzing water trick, i will do that today. . I'm starting to think its overcharged. can one just let some one and keep testing? :-)
09-21-2015, 01:01 PM
#57
Rennlist Member
Not legal, but every guy with an a/c leak is letting out refrigerant.
More important, you only know how much is in the system by recovering and recharging by P & T and weight.
OTOH if some refrigerant leaked out and your numbers got better...
Good luck,
Dave
09-21-2015, 06:38 PM
#59
Recover.
Evacuate.
Recharge with virgin, however, this time....
Charge the system when the engine is at normal operating temperature.
Charge and test at IDLE.
1) Rather than starting off with the known weight of R134a (80-90% of the original R12 weight), start with 16 oz. Let the AC system run for 5 minutes (idle) with this charge.
Note the outside air temp, low and high side pressures.
Here are some reference P&T for the high with R134a at Idle:
75F, 180 psi
80F, 202 psi
85F, 214 psi
90F, 238 psi
2) If your high side is below those reference points then put in another 4 ounces.
Again, let the system run at idle for another 5 minutes and check your high side.
If still below the reference number put in 2 to 4 oz (depends upon how low you are below the bogey.
3) Keep doing that until hit the bogey.
Record the final ambient temp outside, the final low and high side and vent temp at idle. Note if the comp clutch is cycling on and off as much as before.
Note your engine coolant temp.
4) Inspect the evaporator outlet pipe. It should be sweating to frosty. If not
you got other issues.
5) Take the car for ride, 25-40 mph constant drive for 15 minutes.
Note and record the ambient temp and the final vent temp at the end of the
15 minutes.
6) In the end, if all the AC components are functioning normally (compressor is pumping, condenser is not clogged, expansion valve metering, pressure or temperature switches doing their thing),
you had a good evacuation and no air entered the system during charging, your gauges are accurate, your method of measuring weight of refrigerant going in is accurate, the high side pressure
matches up pretty close for the corresponding ambient, you don't have an air flow issue through the condenser (you have 'factory' or better air flow).....
your final R134a amount of refrigerant by weight will be between 80-90% of the factory R12 weight.
Evacuate.
Recharge with virgin, however, this time....
Charge the system when the engine is at normal operating temperature.
Charge and test at IDLE.
1) Rather than starting off with the known weight of R134a (80-90% of the original R12 weight), start with 16 oz. Let the AC system run for 5 minutes (idle) with this charge.
Note the outside air temp, low and high side pressures.
Here are some reference P&T for the high with R134a at Idle:
75F, 180 psi
80F, 202 psi
85F, 214 psi
90F, 238 psi
2) If your high side is below those reference points then put in another 4 ounces.
Again, let the system run at idle for another 5 minutes and check your high side.
If still below the reference number put in 2 to 4 oz (depends upon how low you are below the bogey.
3) Keep doing that until hit the bogey.
Record the final ambient temp outside, the final low and high side and vent temp at idle. Note if the comp clutch is cycling on and off as much as before.
Note your engine coolant temp.
4) Inspect the evaporator outlet pipe. It should be sweating to frosty. If not
you got other issues.
5) Take the car for ride, 25-40 mph constant drive for 15 minutes.
Note and record the ambient temp and the final vent temp at the end of the
15 minutes.
6) In the end, if all the AC components are functioning normally (compressor is pumping, condenser is not clogged, expansion valve metering, pressure or temperature switches doing their thing),
you had a good evacuation and no air entered the system during charging, your gauges are accurate, your method of measuring weight of refrigerant going in is accurate, the high side pressure
matches up pretty close for the corresponding ambient, you don't have an air flow issue through the condenser (you have 'factory' or better air flow).....
your final R134a amount of refrigerant by weight will be between 80-90% of the factory R12 weight.
Last edited by griffiths; 09-22-2015 at 08:35 AM.