Ac help
03-30-2018, 08:35 AM
#1
Ac help
So I am finally getting getting around to work on my ac since the weather is getting warmer. I have tested my vacuum to my heater control valve and the valve itself and both work. My setting motor is also functioning properly, so here is what’s going on: I have vacuum to my valve when the system is set to off, however I have no vacuum to the valve when the system is on. Neither the temperature slider nor the ac button makes a difference in the vacuum. Thoughts?
1986 Porsche 928
1986 Porsche 928
03-31-2018, 03:13 AM
#3
Rennlist
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There are 5 vacuum switches and 4 vacuum pods in the inside of the car. At this point in time, multiples of those items can leak vacuum, which will eliminate all vacuum to the heater control valve.
Also, vacumm supply issues are extremely common.
Start at the power brake booster and make sure you have an ample supply of vacuum past the check valve and into the black plastic hose which goes to the inside of the car.
Remove the driver's side panel on the center console. Start by checking to see if the colored hoses that go from the vacuum control switches to the interior pods all hold vacuum (some very likely will not.) Order and replace the bad vacuum.pods (much easier said than done.)
You can then test the 5 electric/vacuum switches and see if they all hold vacuum, when switched. (Good luck getting to them.)
You should also make sure that the heater control valve, even though it moves, shuts off the water flow. Very common to have an internal O-ring which seals the "door" fail and thus leak hot water past it.
Once you completely repair the vacuum system (since you are starting now, you should be done with the vacuum system by the end of April), you will discover that no matter what you do, heat still "bleeds" through the system with the heater valve closed and all the rest of the vacuum system working.
The foam on the doors inside the HVAC unit will be completely deteriorated and it will be mpossible to get the door between the heater core and the A/C compressor to seal completely, so heat will bleed through all the time. (There's a neat trick to curing this, when you get to this point, BTW.)
Once all of this stuff is repaired, you can then start on repairing the A/C system, which probably hasn't held Freon for the past 20 years. You will find out that there is no power to the compressor and that the HVAC contol in the dash is bad (We do the best rebuilding of this unit, in the country.)
If things go right (and the hose behind the coil on the passenger side of the car doesn't leak, you should get semi-cold air by the end of June. If yiu have a rear A/C unit, you will instantly notice that the front vents will get 19 degrees hotter when you turn on the rear A/C. If you live in a climate that gets above 90 degrees and have expectations of getting enough A/C to not suffocate, we make an A/C conversion kit that will blow huge volumes of very cold air...out of both the front and rear A/C units..
for about the same amount as your car gained in value, this last year.
It's a very funny thing, these days. People will come into my shop with a list of things to repair....and at the very last will say: " If it isn't too involved, see if you can make the A/C work.
That almost never happens....it is almost always very involved, these days. However, we do have an advantage....we fix so many of these things that people don't have to pay us to learn how! We know the steps required, in our sleep.
Also, vacumm supply issues are extremely common.
Start at the power brake booster and make sure you have an ample supply of vacuum past the check valve and into the black plastic hose which goes to the inside of the car.
Remove the driver's side panel on the center console. Start by checking to see if the colored hoses that go from the vacuum control switches to the interior pods all hold vacuum (some very likely will not.) Order and replace the bad vacuum.pods (much easier said than done.)
You can then test the 5 electric/vacuum switches and see if they all hold vacuum, when switched. (Good luck getting to them.)
You should also make sure that the heater control valve, even though it moves, shuts off the water flow. Very common to have an internal O-ring which seals the "door" fail and thus leak hot water past it.
Once you completely repair the vacuum system (since you are starting now, you should be done with the vacuum system by the end of April), you will discover that no matter what you do, heat still "bleeds" through the system with the heater valve closed and all the rest of the vacuum system working.
The foam on the doors inside the HVAC unit will be completely deteriorated and it will be mpossible to get the door between the heater core and the A/C compressor to seal completely, so heat will bleed through all the time. (There's a neat trick to curing this, when you get to this point, BTW.)
Once all of this stuff is repaired, you can then start on repairing the A/C system, which probably hasn't held Freon for the past 20 years. You will find out that there is no power to the compressor and that the HVAC contol in the dash is bad (We do the best rebuilding of this unit, in the country.)
If things go right (and the hose behind the coil on the passenger side of the car doesn't leak, you should get semi-cold air by the end of June. If yiu have a rear A/C unit, you will instantly notice that the front vents will get 19 degrees hotter when you turn on the rear A/C. If you live in a climate that gets above 90 degrees and have expectations of getting enough A/C to not suffocate, we make an A/C conversion kit that will blow huge volumes of very cold air...out of both the front and rear A/C units..
for about the same amount as your car gained in value, this last year.
It's a very funny thing, these days. People will come into my shop with a list of things to repair....and at the very last will say: " If it isn't too involved, see if you can make the A/C work.
That almost never happens....it is almost always very involved, these days. However, we do have an advantage....we fix so many of these things that people don't have to pay us to learn how! We know the steps required, in our sleep.
03-31-2018, 04:06 AM
#4
Rennlist Member
^^ I second what Greg says. Every valve in the system needs to be operating correctly for the system to even have a chance at working.
Before you do what I talk about below, check over what Greg says above. That small black and blue check valve caused mine and others systems to not work correctly and either get no vacuum or leak it back during acceleration.
First thing you should do is remove the center console and hook up a mighty vac to the hvac lines to see which valves are leaking.
You should replace all the diaphragms with silicone ones from Roger as this is the best time to do it as they will fail in the future, most likely sooner than you think.
You need to remove the dash to get at the defrost valve, it isn't actually that hard. remove the gauge cluster, glove box, and parcel trays.
Then remove the center console and then undo the 4 bolts that hold the dash in. It takes about 1.5 hours to do when marking everything carefully.
When the dash is out you can split the HVAC box (reseal it with 3M stripcaulk) and pull out the blending doors, the whole system is very modular and easy to work with.
Scrape off the old foam and adhesive and replace it with 1/8th inch adhesive backed closed cell foam.
Just undo the lines to the heater core and evaporator and they pull out if you really want to clean it (likely full of leaves and other detritus) and replace the o rings in the heater core pipes.
This is the best time to replace the expansion valve as you wont have to bend any hard lines to remove it at this point.
Be sure to flush the evaporator as well before you install the new expansion valve as well as the other hard lines in the system, nobody knows if your compressor has failed and sent metal pieces through the system.
Plus, this will make it easier to convert to r134 if you haven't already or convert back to r12 if you prefer.
Before you put your dash back in, adjust the blend doors and blend motor according to the WSM to ensure proper operation.
Once this is done and put back together, you can then start on really working on the refrigerant side of the system and replace all the o-rings and soft lines with barrier hose and r134 compliant o-rings (they're backwards compatible with r12).
I know this sounds daunting (it is) but every 928 needs to have their HVAC system serviced at this point and yours sounds like it is in need of an overhaul.
Before you do what I talk about below, check over what Greg says above. That small black and blue check valve caused mine and others systems to not work correctly and either get no vacuum or leak it back during acceleration.
First thing you should do is remove the center console and hook up a mighty vac to the hvac lines to see which valves are leaking.
You should replace all the diaphragms with silicone ones from Roger as this is the best time to do it as they will fail in the future, most likely sooner than you think.
You need to remove the dash to get at the defrost valve, it isn't actually that hard. remove the gauge cluster, glove box, and parcel trays.
Then remove the center console and then undo the 4 bolts that hold the dash in. It takes about 1.5 hours to do when marking everything carefully.
When the dash is out you can split the HVAC box (reseal it with 3M stripcaulk) and pull out the blending doors, the whole system is very modular and easy to work with.
Scrape off the old foam and adhesive and replace it with 1/8th inch adhesive backed closed cell foam.
Just undo the lines to the heater core and evaporator and they pull out if you really want to clean it (likely full of leaves and other detritus) and replace the o rings in the heater core pipes.
This is the best time to replace the expansion valve as you wont have to bend any hard lines to remove it at this point.
Be sure to flush the evaporator as well before you install the new expansion valve as well as the other hard lines in the system, nobody knows if your compressor has failed and sent metal pieces through the system.
Plus, this will make it easier to convert to r134 if you haven't already or convert back to r12 if you prefer.
Before you put your dash back in, adjust the blend doors and blend motor according to the WSM to ensure proper operation.
Once this is done and put back together, you can then start on really working on the refrigerant side of the system and replace all the o-rings and soft lines with barrier hose and r134 compliant o-rings (they're backwards compatible with r12).
I know this sounds daunting (it is) but every 928 needs to have their HVAC system serviced at this point and yours sounds like it is in need of an overhaul.
03-31-2018, 06:43 AM
#5
Okay so I guess I need to add that i started test vac system a month ago because I had no diversion in air flow and it all just came out the center vent. I tested all solenoids and diaphragms. All diaphragms worked excluding the footwell and mixing flap. My issue was that the control arm inside the the ccu had came off of the pin that holds it to the arm you adjust. Once it was in place the other three diaphragms started working fine. If this is an issue I can stop and fix those two before moving forward, however i don’t really need those to work for my comfort.
the P.O. states they rebuilt the ccu and converted the system to r134, and this guy is a 928 enthusiast and has been eager to help, so I do feel all of
that part has been done.
again, the valve works and has sufficient vac from the system, as it will close when I turn the system off. That tells me that it should function properly if when I moved the temp slider to cool, but it doesn’t. When adjusting temp slider it does not add the vac to close the valve. Any ideas there? Obviously I can zip tie it closed lime most people but i would rather do it right.
thanm you for your help, and any additional advice would be appreciated.
the P.O. states they rebuilt the ccu and converted the system to r134, and this guy is a 928 enthusiast and has been eager to help, so I do feel all of
that part has been done.
again, the valve works and has sufficient vac from the system, as it will close when I turn the system off. That tells me that it should function properly if when I moved the temp slider to cool, but it doesn’t. When adjusting temp slider it does not add the vac to close the valve. Any ideas there? Obviously I can zip tie it closed lime most people but i would rather do it right.
thanm you for your help, and any additional advice would be appreciated.
03-31-2018, 07:05 AM
#6
Rennlist Member
To me it sounds like your blending door motor isn't working and is stuck on full open and or one or both of your temp sensors has failed.
The blending door motor has contacts inside that tell the system how to adjust depending on temperature detected from both of the temps sensors (one in the air duct for the alternator and another in the center console), slider position, etc. Those can get dirty and cause the system to act weird.
There are also transistors inside of the unit that can burn out as well.
If there is one failed valve it will cause the others to not work. I replaced all but 1 valve in the system in my 81 and it failed causing a large vacuum leak and not allowing the other valves to work.
Get those 2 diaphragms replaced, the center vent mixing valve is very important for the system to work correctly.
If the footwell flap is the one above the fuse panel, that one controls whether inside air is recirculated or outside air is used. It is very important for the AC system to function correctly.
Anyway, you should have max AC function as when you slide the temp switch all the way to the left it will activate a microswitch that will close the heater valve, close the recirc valve, and ignore both temp sensors giving you the coldest temps possible.
But if one valve leaks, you wont get cold air and will get coolish air at best.
The blending door motor has contacts inside that tell the system how to adjust depending on temperature detected from both of the temps sensors (one in the air duct for the alternator and another in the center console), slider position, etc. Those can get dirty and cause the system to act weird.
There are also transistors inside of the unit that can burn out as well.
If there is one failed valve it will cause the others to not work. I replaced all but 1 valve in the system in my 81 and it failed causing a large vacuum leak and not allowing the other valves to work.
Get those 2 diaphragms replaced, the center vent mixing valve is very important for the system to work correctly.
If the footwell flap is the one above the fuse panel, that one controls whether inside air is recirculated or outside air is used. It is very important for the AC system to function correctly.
Anyway, you should have max AC function as when you slide the temp switch all the way to the left it will activate a microswitch that will close the heater valve, close the recirc valve, and ignore both temp sensors giving you the coldest temps possible.
But if one valve leaks, you wont get cold air and will get coolish air at best.