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I have brought up my AC refresh projects already. Now I need some help troubleshooting. Today I paid some close attention to how the system is performing. With the AC off, fan on full, always set to recirculating, I used a temperature probe in the vents, and get ambient air temp of 90 deg. With the compressor switched on I get 10 deg. F of cooling. This while driving at 30-35 mph with rpms kept in the 2000 range.
Things I have done:
New compressor within this year (replacement of one that had premature failure - perhaps a hint?) converted to R-134 with first compressor change.
New Evaporator and expansion valve and dryer. I did this myself and was very careful to follow guidance here and best practices discussed in several posts. I have confidence in my work (except the charge - see below).
Have had two separate shops check the pressures. Both say we are in the correct range on the gauges.
I have blocked both heat feeds at the cabin floorboard. So there is zero heat leaking into the system. I do not need heat in my climate.
After replacing the evaporator I had satisfactory cooling (not measured). Maybe not best in class, but I was initially pleased. Summer has come and gone, and the Delta T measured today is not acceptable.
Again, pressures have been checked as adequate.
One thing I am concerned about is that I do not feel I gave the system a proper vacuum prior to charge. I was unable to ensure extended vacuum due to the gauge set available. However I gave it best effort. My plan for today was to have the system evacuated and re-charged, but the shop suggested it was "as good as it gets". But 10 degrees change in temperature is not the best I have seen from others here. For AC service I am not feeling confident in both shops - although for other things I have had very good experience with them. I'm thinking I need an AC specialist.
Shop says everything appears to be working properly. Condenser fan has both speeds, no heat coming in, compressor switching on/off, pressures at the right levels (I do not know measurements).
With the above efforts, where should I be focused?
Flush the system for potential contaminants?
Perform a complete evacuation and recharge?
Can the air leak around the evaporator somehow? If any flappers are not right? Even if fresh air comes in it would go through the evaporator, right?
I did a recent ac refresh on my 993 recently, so not apples to apples ... but I think your doubt on the evacuation would lead me to get it done again first before tearing into the system again. I was fortunate to have vacuum pumps and a good vacuum gage (and time) so I did a 48 hour rise test and then proceeded when i was happy a) no applicable leakage over 48 hours and b) final vacuum level was good. Then charged to specs.
Good luck.
I assume you blocking of the heater hoses is done so no heat can come from the heat exchangers, and no air can be sucked into the air box from the cabin.
This will ensure that all air is drawn through the recirculation opening, and not elsewhere.
The main regulating element for the compressor clutch is the evaporator sensor. This will shut off the clutch when the evap temp reaches 4°C. If this sensor is misplaced, it could reach this temperature earlier than intended. I normally see 10-30 second on/off intervals of the clutch in 22°C ambient temperatures. If yours does the same, I would expect the evap/sensor to behave normally.
A 10 degree lowering of temperature is not far from the specification. See picture below.
The normal is to get 7 to 9°C at the vents in 22°C ambient temp. Car in shade, A/C on, max fan and temperature set to minimum. (this will also engage the recirc function)
If the fresh air vent does not close as designed, (very common servo issue) the fresh air will be of higher temp than the cabin recirculated air, and recirculation will of course not work. You will then experience higher cabin temp than with a working system using recirc to get within the spec. Here's a DIY procedure to test all servo motors: https://www.bergvillfx.com/categorie...test-procedure
Cheers,
Tore
I assume you blocking of the heater hoses is done so no heat can come from the heat exchangers, and no air can be sucked into the air box from the cabin.
This will ensure that all air is drawn through the recirculation opening, and not elsewhere.
The main regulating element for the compressor clutch is the evaporator sensor. This will shut off the clutch when the evap temp reaches 4°C. If this sensor is misplaced, it could reach this temperature earlier than intended. I normally see 10-30 second on/off intervals of the clutch in 22°C ambient temperatures. If yours does the same, I would expect the evap/sensor to behave normally.
A 10 degree lowering of temperature is not far from the specification. See picture below.
The normal is to get 7 to 9°C at the vents in 22°C ambient temp. Car in shade, A/C on, max fan and temperature set to minimum. (this will also engage the recirc function)
If the fresh air vent does not close as designed, (very common servo issue) the fresh air will be of higher temp than the cabin recirculated air, and recirculation will of course not work. You will then experience higher cabin temp than with a working system using recirc to get within the spec. Here's a DIY procedure to test all servo motors: https://www.bergvillfx.com/categorie...test-procedure
Cheers,
Tore
According to the graph, at 25C (77F) the vent temp should be 7.5C (45F) to 11C (52F). this represents a Delta T of at least 25 deg. F. I am getting 10.
I have blocked the heat mostly to remove the variable (would like to reconnect at least one side once the system is cooling properly). Also keeping the recirc setting held constant should remove whatever variable leakage from the outside. Temp outside during my testing was nearly the same as ambient anyway, so I think I am getting a reasonable test of system "on" vs. system "off". So if my recirc flap is leaking it is always leaking. I could block the inlet in a crude way to ensure that is not happening but from my measurements it seems the issue is cooling delta.
Placement of the temp probe would suggest a problem that has been with me since re-assembly, but I believe strongly my system performance has varied over time. I have confidence the probe was assembled as it was removed (although I do not know it was placed properly beforehand). I believe I was removing the factory evap, but no way to be sure. I will test the compressor on/off dwell with a stop watch today.
I did a recent ac refresh on my 993 recently, so not apples to apples ... but I think your doubt on the evacuation would lead me to get it done again first before tearing into the system again. I was fortunate to have vacuum pumps and a good vacuum gage (and time) so I did a 48 hour rise test and then proceeded when i was happy a) no applicable leakage over 48 hours and b) final vacuum level was good. Then charged to specs.
Good luck.
This was my plan yesterday. But the mechanic reviewed the system and thought it was doing what it was capable of. Suggestion was to return on a hotter day. I was disappointed we did not go through with the process hence my frustration. I wonder also if the system needs to be flushed? Having a failed compressor - would that potentially contaminate the system? Could the tiny orifice be blocked? Would this cause weakened cooling capacity?
In my past experience, I've never seen anyone attempt to refurbish their a/c piecemeal and achieve satisfactory results, myself included. Any one component in the chain can foul the attempts to deliver cool air to the cabin. There's not a lot of leeway.
You replaced the evaporator, expansion valve and compressor. What about the condenser, receiver dryer and lines?
It's important to replace the condenser with a parallel flow configuration; one that can reject more heat from the refrigerant. Also, the air damming around the condenser will perished as well. Cooling air cannot be allowed to bypass the condenser so that was something I had to replace.
When I opened up my suitcase, all the foam seals had disintegrated, necessitating a complete refurbishment. It is extremely important that the seals are in good shape to stop warm air infiltration.
All of the obsolete and disintegrating rubber lines on the hard lines were replaced. This afforded me the opportunity to flush the lines as well. If those hoses aren't replaced, you will be charging your system every year and and a/c performance in August won't make you happy.
Any time you open the system up you should replace the receiver dryer.
Perhaps you should give Griffiths Technical a call. I'm sure they can help guide you.
Last edited by Metal Guru; 10-09-2022 at 07:39 PM.
Can you get the temperature of the suction line into the compressor? The delta T of a well designed evaporator is not less than 10 degreesF (meaning that a evap coil that's at 40 deg F will exit air flow at 50 Deg F), add another 10 degrees F because your measuring the temp not in the evap but at the compressor.
So if the surface temp of the suction line is 60 deg F, the evap is at 40 Deg F, and the air from the vents should be around 50 Deg F. That's if all the air flow is throught the evap, no by-passing. Then you need a guage set on the car to get the high side/ low side pressures as the compressor cycles on/off. It could be that the compressor is cycling on high head pressure, because of inadequate cooling air flow across the condenser, or blockage at the expansion valve. Is the suction pressure lower than expected when the compressor cycles on? Could be expansion valve blockage or air by-passing the evap. Another thing you can look at is the sight glass on top of the dryer - is it solid liquid or mostly bubbles ? That indicates the charge level of the system.
The suggestion from your mechanic to return on a hotter day says he doesn't know A/C systems, unless his shop is located in antarctica.
If you evacuate the system again, the shop should check for a pressure leak before drawing a vacuum. The pressure test using the refrigerant that's in the system and using a soapy solution on all hose connections, dryer site glass, crimped connections, etc.. Then the shop should pump down the system with a reclaimation unit (measuring the amount removed) and then evacuate while using a micron guage, to verify that the degree of vacuum.
Can you get the temperature of the suction line into the compressor? The delta T of a well designed evaporator is not less than 10 degreesF (meaning that a evap coil that's at 40 deg F will exit air flow at 50 Deg F), add another 10 degrees F because your measuring the temp not in the evap but at the compressor.
So if the surface temp of the suction line is 60 deg F, the evap is at 40 Deg F, and the air from the vents should be around 50 Deg F. That's if all the air flow is throught the evap, no by-passing. Then you need a guage set on the car to get the high side/ low side pressures as the compressor cycles on/off. It could be that the compressor is cycling on high head pressure, because of inadequate cooling air flow across the condenser, or blockage at the expansion valve. Is the suction pressure lower than expected when the compressor cycles on? Could be expansion valve blockage or air by-passing the evap. Another thing you can look at is the sight glass on top of the dryer - is it solid liquid or mostly bubbles ? That indicates the charge level of the system.
The suggestion from your mechanic to return on a hotter day says he doesn't know A/C systems, unless his shop is located in antarctica.
If you evacuate the system again, the shop should check for a pressure leak before drawing a vacuum. The pressure test using the refrigerant that's in the system and using a soapy solution on all hose connections, dryer site glass, crimped connections, etc.. Then the shop should pump down the system with a reclaimation unit (measuring the amount removed) and then evacuate while using a micron guage, to verify that the degree of vacuum.
THIS is the stuff I need. And also an expert local technician. Now to find that person. I agree with your assessment of my otherwise excellent mechanic.
I don't have a good way to access the sight glass now so I will leave this up to the tech. Also the gauges I used are hundreds of miles away across a hurricane devastation zone so my DIY efforts are over.
I suspect the expansion valve is plugged. And I don't like the sound of that.
In my past experience, I've never seen anyone attempt to refurbish their a/c piecemeal and achieve satisfactory results, myself included. Any one component in the chain can foul the attempts to deliver cool air to the cabin. There's not a lot of leeway.
You replaced the evaporator, expansion valve and compressor. What about the condenser, receiver dryer and lines?
It's important to replace the condenser with a serpentine configuration; one that can reject more heat from the refrigerant. Also, the air damming around the condenser will perished as well. Cooling air cannot be allowed to bypass the condenser so that was something I had to replace.
When I opened up my suitcase, all the foam seals had disintegrated, necessitating a complete refurbishment. It is extremely important that the seals are in good shape to stop warm air infiltration.
All of the obsolete and disintegrating rubber lines on the hard lines were replaced. This afforded me the opportunity to flush the lines as well. If those hoses aren't replaced, you will be charging your system every year and and a/c performance in August won't make you happy.
Any time you open the system up you should replace the receiver dryer.
Perhaps you should give Griffiths Technical a call. I'm sure they can help guide you.
Good tips. I would have used the Griffith's evap if I could have. I did replace the dryer, not the lines and condenser. I'm pretty confident in the suitcase re-assembly.
Took the car to an AC shop in little Havana. Went through the negotiation from "we have to do a full diagnosis" standard starting point and after fully discussing all that has been done and saying it must be brought back to R12 (a potential long term solution), we did a evacuation and recharge with R134. Turns out it was low on refrigerant, and worked well after recharge. Delta T from 80 in the garage to 48 on the street. I get low 50's after sitting in the shade and interior temp getting to 90. I'm happy for now.
So, my understanding is the R134 is leaking through the hoses, at least - potential for other leaks still exist. And with this issue I will need to continuously recharge.
Or, if no connection leaks I can try going back to R12. they said the system will work as is (same compressor). So I have a quote to do that as well.
Went through the negotiation from "we have to do a full diagnosis" standard starting point and after fully discussing all that has been done and saying it must be brought back to R12.
It's fine to say that you will recharge the R-134a when the air stops working but do you really want to screwing around with charging the system every year?
What if you can't find R-12? Where I live, there's no R-12 available nor a shop willing to charge with it. That could be your situation eventually too.
Good luck with whatever you eventually end up doing.
Also, to run R-134a effectively, a parallel flow condenser is recommended (I originally said serpentine flow).
Know this though, going back to R12, is it truly R12 or a drop-in replacement of R12? Because R12 is hard to get, there are R12 replacements that are blends of other refrigerants, and gases and the mix has physical properties similar to R12 ( boiling point, molecular weight, etc.) This blend probably is a blend of HFC 134A, HFC 125, butane, isopentane which will leak through a non-barrier hose in proportion to molecular size of each gas. If you use a drop-in replacement and you leak one of the components, as you top off the system over time the system becomes full of every gas that doesn't leak missing the component that does leak. Or if you top off with true R12 the new mix will have issues ( azeotropic, different boiling points of the liquid forms).
I've owned my car since 2000 and I used R12 at first, then Freeze 12 ( a drop-in replacement) around 2002, then switched over to 134A sometime in 2005 when Freeze 12 became hard to get in California, then replaced hoses to barrier hoses( new evap. and condenser also) in 2014. I think there's a hole in the ozone layer named after me as I piecemealed this 134A conversion over time.
Last edited by mojorizing; 10-12-2022 at 03:56 PM.
It's fine to say that you will recharge the R-134a when the air stops working but do you really want to screwing around with charging the system every year?
What if you can't find R-12? Where I live, there's no R-12 available nor a shop willing to charge with it. That could be your situation eventually too.
Good luck with whatever you eventually end up doing.
Also, to run R-134a effectively, a parallel flow condenser is recommended (I originally said serpentine flow).
He mentioned another condenser. Is this mounted int he engine compartment? With another fan perhaps? I did not get the connection in my brain at first. So yes, this may be a mod I need. And as you have mentioned, new hoses. This could be the biggest challenge having the car as in Miami we need good AC. I'll keep after it.
Know this though, going back to R12, is it truly R12 or a drop-in replacement of R12? Because R12 is hard to get, there are R12 replacements that are blends of other refrigerants, and gases and the mix has physical properties similar to R12 ( boiling point, molecular weight, etc.) This blend probably is a blend of HFC 134A, HFC 125, butane, isopentane which will leak through a non-barrier hose in proportion to molecular size of each gas. If you use a drop-in replacement and you leak one of the components, as you top off the system over time the system becomes full of every gas that doesn't leak missing the component that does leak. Or if you top off with true R12 the new mix will have issues ( azeotropic, different boiling points of the liquid forms).
I've owned my car since 2000 and I used R12 at first, then Freeze 12 ( a drop-in replacement) around 2002, then switched over to 134A sometime in 2005 when Freeze 12 became hard to get in California, then replaced hoses to barrier hoses( new evap. and condenser also) in 2014. I think there's a hole in the ozone layer named after me as I piecemealed this 134A conversion over time.
You guys have the experience I need to follow. I should be planning for new hoses as my next big job. And yeah, I should have done it with the evap. Maybe by the time I get primed to take this on I will be able to get the Griffith's evaporator upgrade. I really don't want to be having this chemical discussion with the boys in little Havana. They don't like the gringos as it is.
10-06-2022, 09:29 PM
Need AC expert help - really frustrated
