What happens if the receiver - drier is in backwards? S4
06-20-2014, 03:18 AM
#2
Chronic Tool Dropper
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Flow through the dessicant bag inside the drier is from outside in when installed correctly. Similar to the way an oil filter is built, the intent is to make sure that filter congestion amd resultant pressure drop do not cause the filter media to come apart. In the case of the drier, the dessicant starts out as beads in the bag. The beads become oil-saturated in use and end up more like firm jelly blobs similar in texture to partially-cured RTV. When a drier bag ruptures, those jelly blobs circulate to the expansion valve, where they restrict flow. A few might get through and start to block the evaporator but the expansion valve usually plugs up fast enough to limit how much gets in there. In cases where the bag rupture is small and flow continues at close to normal rate, the soggy beads will make it all the way to the compressor. They block the reeds open and pumping pretty much stops.
I'd sure think hard about fixing it if it really is in backwards. I don't have the car handy, but my foggy memory is that you can't put it in backwards. Don't hold me to it.
I'd sure think hard about fixing it if it really is in backwards. I don't have the car handy, but my foggy memory is that you can't put it in backwards. Don't hold me to it.
06-20-2014, 03:25 AM
#3
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06-20-2014, 09:49 AM
#5
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One of the functions of the receiver/dryer is to give solid liquid flow to the expansion valve. Think of a can with the inlet being a short tube at the top, dribbling fluid from the condenser. The liquid refrigerant dribbles thru the filter/dryer media and collects at the bottom of the can. The outlet is a long tube, going to the bottom of the can to pick up a solid flow of liquid.
Backwards won't work well, if at all.
Backwards won't work well, if at all.
06-20-2014, 11:11 AM
#6
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It is absolutely possible to put it in backwards. I've had to correct that situation on several occasions.
06-20-2014, 11:26 AM
#7
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Yes, they can go in backwards. So my question is what is the correct way to install? The "IN" goes left or right side when facing engine. This would put the pressure switches on the right side. I believe we have determined it goes closest to the pressure switch.
Thomas
Thomas
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06-20-2014, 12:27 PM
#9
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"Right" and "Left" on the car are ALWAYS determined based on normal direction of travel, so looking from the front at the drier, those terms can be confusing. That said, the INLET of the drier receives refrigerant from the condenser, while the OUTLET connects to the line down the passenger side inner fenderwall that carries refrigerant to the expansion valve. The little switch manifold sits on the DRIVERS side (for US LHD cars) of the drier, between the condenser and the drier inlet.
And that "most AC miles with the receiver/drier installed backwards" is not a record I'm willing to compete for, at least not on purpose.
FWIW, if you do somehow manage to get the drier in backwards, .and. you charge by the sightglass without looking at gauges, you quite likely have a LOT of extra refrigerant in your system with high pressures and poor performance.
And that "most AC miles with the receiver/drier installed backwards" is not a record I'm willing to compete for, at least not on purpose.
FWIW, if you do somehow manage to get the drier in backwards, .and. you charge by the sightglass without looking at gauges, you quite likely have a LOT of extra refrigerant in your system with high pressures and poor performance.
06-20-2014, 01:15 PM
#10
Racer
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As Dr Bob suggests, the record should be for the most AC miles with the receiver/drier inadvertently installed backwards. 
Here's another explanation of the process inside the receiver-drier from this thread:
BTW, who would have guessed that 'desiccant' has one 's' and two 'c's'? Not me.
Here's another explanation of the process inside the receiver-drier from this thread:
The receiver/dryer, as the name implies, has two functions. It contains a dessicant to remove any water that got left in the system. The "receiver" function means it receives the two-phase (gas and liquid) high-pressure freon from the condenser. The function of the receiver is to provide a volume to separate the liquid and gas phase by gravity. Two-phase mixed flow enters at the top. The liquid goes to the bottom, and the lighter gas phase goes to the top. The same thing happens when you pour beer into a glass. The liquid goes to the bottom, and the foam goes to the top.
The exit line from the receiver is connected to a tube that draws only the liquid phase from the bottom of the receiver. Liquid freon goes to the expansion valve, where the pressure is dropped. The liquid boils back to the gas phase as it travels through the evaporator. "Angel's breath" is produced when the cabin air is blown through the cold evaporator. A properly charged system has cold gas at the compressor suction, hot gas at the compressor discharge, hot two-phase flow in the condensor, hot liquid going to the expansion valve, and then cold two-phase flow in the evaporator. A critical step in the process is separation of the liquid and gas phases in the receiver.
If your receiver really is backwards, the two phase freon enters through the tube at the bottom. Gravity separation will still occur, although the fresh freon entering at the bottom will certainly keep things stirred up. You will still have mostly gas phase at the top where the incorrect "discharge" port will send mostly vapor to the expansion valve and evaporator.
There are only two ways you could be getting good cooling:
1) It is a relatively cool day, so you are not operating near capacity
2) Your system is so over-charged that the condenser is already fully liquid before it reaches the receiver dryer.
In the second case, you are operating with very little gas cushion in the system. The compressor discharge pressure is way too high. You risk bursting a hose or damaging the compressor. You will certainly consume too much engine power for the cooling you are getting.
If you still don't believe me, get your system on a set of pressure gages and read the system pressures. With the receiver in backwards, you will have high compressor discharge pressure and very low system efficiency. You live in a cool climate, and you have a system designed for Saudi Arabia. If you want to take advantage of the system's high margin for your climate, that is fine with me. However, the AC compressor is very powerful, and capable of extremely high pressure. It is quite dangerous to abuse powerful equipment. Please refrain from encouraging others to install backward parts. Somebody could come to grief.
The exit line from the receiver is connected to a tube that draws only the liquid phase from the bottom of the receiver. Liquid freon goes to the expansion valve, where the pressure is dropped. The liquid boils back to the gas phase as it travels through the evaporator. "Angel's breath" is produced when the cabin air is blown through the cold evaporator. A properly charged system has cold gas at the compressor suction, hot gas at the compressor discharge, hot two-phase flow in the condensor, hot liquid going to the expansion valve, and then cold two-phase flow in the evaporator. A critical step in the process is separation of the liquid and gas phases in the receiver.
If your receiver really is backwards, the two phase freon enters through the tube at the bottom. Gravity separation will still occur, although the fresh freon entering at the bottom will certainly keep things stirred up. You will still have mostly gas phase at the top where the incorrect "discharge" port will send mostly vapor to the expansion valve and evaporator.
There are only two ways you could be getting good cooling:
1) It is a relatively cool day, so you are not operating near capacity
2) Your system is so over-charged that the condenser is already fully liquid before it reaches the receiver dryer.
In the second case, you are operating with very little gas cushion in the system. The compressor discharge pressure is way too high. You risk bursting a hose or damaging the compressor. You will certainly consume too much engine power for the cooling you are getting.
If you still don't believe me, get your system on a set of pressure gages and read the system pressures. With the receiver in backwards, you will have high compressor discharge pressure and very low system efficiency. You live in a cool climate, and you have a system designed for Saudi Arabia. If you want to take advantage of the system's high margin for your climate, that is fine with me. However, the AC compressor is very powerful, and capable of extremely high pressure. It is quite dangerous to abuse powerful equipment. Please refrain from encouraging others to install backward parts. Somebody could come to grief.
06-20-2014, 01:57 PM
#11
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As soon as I read 'caviar' it triggered my 928 A/C PTSD. The good news is that 4 years later the A/C still works well on the GTS.
I honestly don't know whether the receiver drier was installed backwards before I bought the car, or whether it was installed properly and whatever screen holds the caviar back just failed. I do know that the A/C didn't work when I first bought the GTS and drove it home.
(I have to confess that I didn't change the receiver-dryer when I installed the engine, as the system had not been opened during the stroker install. It was only when I decided to chase down the lack of cold that I discovered the caviar.
I honestly don't know whether the receiver drier was installed backwards before I bought the car, or whether it was installed properly and whatever screen holds the caviar back just failed. I do know that the A/C didn't work when I first bought the GTS and drove it home.
(I have to confess that I didn't change the receiver-dryer when I installed the engine, as the system had not been opened during the stroker install. It was only when I decided to chase down the lack of cold that I discovered the caviar.
06-20-2014, 02:12 PM
#12
Racer
Thread Starter
Rob,
Those were scary photos. Unfortunately, unless you can document that the R/D was installed backwards you are not eligible for the record.
(Now we'll see if some photos miraculously appear - as usual. It's not the photos that are amazing to me although they are always very good - it's the retrieval).
Those were scary photos. Unfortunately, unless you can document that the R/D was installed backwards you are not eligible for the record.
(Now we'll see if some photos miraculously appear - as usual. It's not the photos that are amazing to me although they are always very good - it's the retrieval).
06-20-2014, 02:18 PM
#13
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Thank you for this clear description. I will go back and change the position of dryer for the 3rd time. This AC system has not been run as of yet so no wasted R12. Just installed new Denso and dryer, and I was confused by description on flow in service manual on early cars.+
Thomas
Thomas
"Right" and "Left" on the car are ALWAYS determined based on normal direction of travel, so looking from the front at the drier, those terms can be confusing. That said, the INLET of the drier receives refrigerant from the condenser, while the OUTLET connects to the line down the passenger side inner fenderwall that carries refrigerant to the expansion valve. The little switch manifold sits on the DRIVERS side (for US LHD cars) of the drier, between the condenser and the drier inlet.
And that "most AC miles with the receiver/drier installed backwards" is not a record I'm willing to compete for, at least not on purpose.
FWIW, if you do somehow manage to get the drier in backwards, .and. you charge by the sightglass without looking at gauges, you quite likely have a LOT of extra refrigerant in your system with high pressures and poor performance.
And that "most AC miles with the receiver/drier installed backwards" is not a record I'm willing to compete for, at least not on purpose.
FWIW, if you do somehow manage to get the drier in backwards, .and. you charge by the sightglass without looking at gauges, you quite likely have a LOT of extra refrigerant in your system with high pressures and poor performance.
06-20-2014, 04:20 PM
#14
Archive Gatekeeper
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It occurs to me that the receiver dryer is different in the GTS, owing to the switch to r134a. Bottom line, I don't think you _can_ install a GTS drier backwards.
Here's the top of the (failed) dryer that was in my car. Front of the car would be towards the left.
So the inlet from the condenser is at the front of the car, and the outlet is in the middle of the drier.
And the underside of the little T-shaped line fitting/overpressure valve that attaches (only 1 way) to the drier (note caviar..):
Topside:
Drier in situ:
Here's the top of the (failed) dryer that was in my car. Front of the car would be towards the left.
So the inlet from the condenser is at the front of the car, and the outlet is in the middle of the drier.
And the underside of the little T-shaped line fitting/overpressure valve that attaches (only 1 way) to the drier (note caviar..):
Topside:
Drier in situ:
