a/c rebuild ignorance (long)
05-09-2004, 01:46 PM
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a/c rebuild ignorance (long)
For those that haven't been following, I'm in the middle of rebuilding my a/c system including converting the compressor over to a Sanden unit as part of a (possible) r134a conversion (the debate on whether I should ultimately charge up with r12 or r134 still rages in another thread), along with two lines to the evaporator located up under the dash on the passenger's side. I'm curious about what the exact flow of refrigerant is through the system.
Bear in mind I've never worked on an a/c system before, so a lot of this is new to me: I'd like to know how the refrigerant moves around in the system so I have a better idea of what to connect where - nothing is labeled and the instructions that came with my Sanden kit are quite inadequate about anything other than how to connect the compressor to the bracket in the car.
Starting with the compressor: there are two lines on the new Sanden (and on the older Nippondenso it's replacing), a "big" connector that goes to a hose along the fenderwell, the firewall and ultimately to the evaporator. Coming back is the other hose I'm replacing: a smaller diameter one that goes to the receiver / drier. The receiver drier (little cylinder with sight glass) has another hose coming off of it that goes (I think) to the condenser, but I haven't traced it yet. Finally there's another line that comes off of the bottom of the condenser and back to the compressor.
OK, I'm guessing that the line off the bottom of the condenser is the "supply" to the compressor since it's at the bottom of the condenser, that's where "condensed" refrigerant would settle out, right? So this line should go to the side of the compressor labeled "SUPPLY", right?
Next, the compressor "compresses" the refrigerant to make it a hot gas. This gaseous refrigerant gets ducted via the big hose I'm replacing to the evaporator (so this should get connected to the side of the compressor labeled "DISCHARGE", right?) I'm thinking that there's supposed to be an expansion valve somewhere before the evaporator that "mists" the refrigerant and rapidly cools it to a liquid due to rapid pressure drop, but I haven't found any such thing. Maybe it's integrated with the evaporator (???)
From the evaporator, the refrigerant is supposedly now a liquid carrying only the heat picked up from the interior cabin of the car, goes back to the receiver / drier, and waits for a thermally-actuated valve to open. When it does, the liquid refrigerant is pumped to the condenser and then to the compressor to complete the cycle.
So my questions are this:
(1) is my naive understanding of a/c systems correct as it pertains to the routing of stuff in the car?
(2) does the refrigerant flow in the manner described or do I have something messed up?
(3) where the heck is the expansion valve?
(4) what exactly does the condenser do? The refrigerant is liquid at the point it comes in (I think the top) of the condenser already, right? Why does it then need to be "condensed" further or is it just to cool it as much as possible before feeding it to the compressor?
(5) There is a thermal valve-looking thing that came with the kit, it has two threaded connectors on it and a copper coil. I see no corresponding part in the existing system. Where does this go and what does it do?
(6) The new compressor comes with two 90-degree fittings that have nipples on the end for a piece of hose to fit over and then get clamped down upon from the outside. Since the "discharge" from the compressor goes into an "existing" hose (I'm replacing it, but the diagram calls it "existing") with a threaded connector, how the heck am I supposed to hook this together? Do they actually expect me to cut a $300 hose?!?!
(7) There are two bicycle-tire looking valve stems (Schraeder valves) covered by caps on the back of the compressor, one labeled "SUPPLY" and one labeled "DISCHARGE". Is this where the refrigerant gets added? If so, which kind (I thought the valve type was supposed to be different for r134 and r12). Which one? Should it be added to the "SUPPLY" or the "DISCHARGE" one?
(8) The offending 90-degree bent tube that is supposed to SOMEHOW hook up to the big hose running to the evaporator has yet ANOTHER Schraeder valve on it. Is this even necessary? It looks like I can connect the big threaded hose directly to the compressor and not worry about how it hooks up to this 90-degree elbow thingy, but if so, why'd they give it to me and why is it on their drawings?
I'll post pics on the progress later. Thanks for looking.
Bear in mind I've never worked on an a/c system before, so a lot of this is new to me: I'd like to know how the refrigerant moves around in the system so I have a better idea of what to connect where - nothing is labeled and the instructions that came with my Sanden kit are quite inadequate about anything other than how to connect the compressor to the bracket in the car.
Starting with the compressor: there are two lines on the new Sanden (and on the older Nippondenso it's replacing), a "big" connector that goes to a hose along the fenderwell, the firewall and ultimately to the evaporator. Coming back is the other hose I'm replacing: a smaller diameter one that goes to the receiver / drier. The receiver drier (little cylinder with sight glass) has another hose coming off of it that goes (I think) to the condenser, but I haven't traced it yet. Finally there's another line that comes off of the bottom of the condenser and back to the compressor.
OK, I'm guessing that the line off the bottom of the condenser is the "supply" to the compressor since it's at the bottom of the condenser, that's where "condensed" refrigerant would settle out, right? So this line should go to the side of the compressor labeled "SUPPLY", right?
Next, the compressor "compresses" the refrigerant to make it a hot gas. This gaseous refrigerant gets ducted via the big hose I'm replacing to the evaporator (so this should get connected to the side of the compressor labeled "DISCHARGE", right?) I'm thinking that there's supposed to be an expansion valve somewhere before the evaporator that "mists" the refrigerant and rapidly cools it to a liquid due to rapid pressure drop, but I haven't found any such thing. Maybe it's integrated with the evaporator (???)
From the evaporator, the refrigerant is supposedly now a liquid carrying only the heat picked up from the interior cabin of the car, goes back to the receiver / drier, and waits for a thermally-actuated valve to open. When it does, the liquid refrigerant is pumped to the condenser and then to the compressor to complete the cycle.
So my questions are this:
(1) is my naive understanding of a/c systems correct as it pertains to the routing of stuff in the car?
(2) does the refrigerant flow in the manner described or do I have something messed up?
(3) where the heck is the expansion valve?
(4) what exactly does the condenser do? The refrigerant is liquid at the point it comes in (I think the top) of the condenser already, right? Why does it then need to be "condensed" further or is it just to cool it as much as possible before feeding it to the compressor?
(5) There is a thermal valve-looking thing that came with the kit, it has two threaded connectors on it and a copper coil. I see no corresponding part in the existing system. Where does this go and what does it do?
(6) The new compressor comes with two 90-degree fittings that have nipples on the end for a piece of hose to fit over and then get clamped down upon from the outside. Since the "discharge" from the compressor goes into an "existing" hose (I'm replacing it, but the diagram calls it "existing") with a threaded connector, how the heck am I supposed to hook this together? Do they actually expect me to cut a $300 hose?!?!
(7) There are two bicycle-tire looking valve stems (Schraeder valves) covered by caps on the back of the compressor, one labeled "SUPPLY" and one labeled "DISCHARGE". Is this where the refrigerant gets added? If so, which kind (I thought the valve type was supposed to be different for r134 and r12). Which one? Should it be added to the "SUPPLY" or the "DISCHARGE" one?
(8) The offending 90-degree bent tube that is supposed to SOMEHOW hook up to the big hose running to the evaporator has yet ANOTHER Schraeder valve on it. Is this even necessary? It looks like I can connect the big threaded hose directly to the compressor and not worry about how it hooks up to this 90-degree elbow thingy, but if so, why'd they give it to me and why is it on their drawings?
I'll post pics on the progress later. Thanks for looking.
05-09-2004, 01:55 PM
#2
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Here's what I know:
The expansion valve is fitted at the evaporator. You will need to pull the evaporator from the car to install it. Evaporator is located behind the glove box and is accessed from the passenger side footwell.
I had the conversion done professionally with a Sanden kit also, so I can't attest to what was done with the hoses, but I have since replaced the condenser and recharged the system myself with R134a.
If you intend to do it yourself, you should get a "charge kit" like the one from "Interdynamics" at your local Walmart, etc. and follow the instructions. The "supply" inlet on the compressor is where you charge the system with R134a.
The stuff blows ice cold, so I don't see a problem with using it instead of the "illegal" R12.
The expansion valve is fitted at the evaporator. You will need to pull the evaporator from the car to install it. Evaporator is located behind the glove box and is accessed from the passenger side footwell.
I had the conversion done professionally with a Sanden kit also, so I can't attest to what was done with the hoses, but I have since replaced the condenser and recharged the system myself with R134a.
If you intend to do it yourself, you should get a "charge kit" like the one from "Interdynamics" at your local Walmart, etc. and follow the instructions. The "supply" inlet on the compressor is where you charge the system with R134a.
The stuff blows ice cold, so I don't see a problem with using it instead of the "illegal" R12.
05-09-2004, 02:09 PM
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You WERE able to get the evaporator out without removing the entire dash??? YES!!! That's the news I've been waiting to hear. Thanks, I'm off to do it now. Much appreciated.
05-09-2004, 02:25 PM
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Sweet. That'll make life a heck of a lot simpler. I sort of thought this could be done, but everyone I asked seemed to think it required removal of the entire dash (ugh). I'll let you know how it goes.
05-09-2004, 02:46 PM
#6
Three Wheelin'
POP: I found this site when sourcing a/c parts, a lot of people on the list recommend these guys. Their site has a lot of information on it, including the R12 134a debate...
http://www.griffiths.com/achelp/achelp1.htm
Good Luck!
Erich
http://www.griffiths.com/achelp/achelp1.htm
Good Luck!
Erich
05-09-2004, 02:56 PM
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Originally posted by Luis de Prat
Here's what I know:
The stuff blows ice cold, so I don't see a problem with using it instead of the "illegal" R12.
Here's what I know:
The stuff blows ice cold, so I don't see a problem with using it instead of the "illegal" R12.
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05-09-2004, 03:40 PM
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Originally posted by seb928s
It's not illegal to use with proper tools and can be bought in town if you have the license to.
It's not illegal to use with proper tools and can be bought in town if you have the license to.
Originally posted by seb928s
R12 will cool better in very hot days. In Florida I know a few that went with the R134a and don't like it cause it doesn't cool enough.
R12 will cool better in very hot days. In Florida I know a few that went with the R134a and don't like it cause it doesn't cool enough.
05-10-2004, 09:49 AM
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Thanks guys - well the good news is the evaporator came out VERY easily - I think it required removing a total of ten screws for the glove box & lower dash panel, then four 10mm bolts to drop the evaporator. The fittings of the offending hoses are right in front and easy to get at (imagine my ecstasy!).
The hoses are a major PITA to re-route though - I ended up having to cut out the old "large" line (since it was diagnosed as leaking anyway, I didn't care) the one that goes from the evaporator to the compressor. I found that it was easiest (or should I say least difficult) to route the smaller hose through the firewall from the outside and push the large one out from the inside. I removed the smaller one first to make getting at the big one easier. In Haynes fashion, installation was the opposite of removal. Good deal though - those (%($&(& hoses are in!
Other major problem though: the nice new Sanden compressor doesn't fit!!!
When it hangs on the bracket, in order to swing it over to get the drive belt over it, it bangs against the bracket (limits its movement). The alternator is already at the limit of its movement to provide the most slack and the only other thing that belt goes over is the crank pulley (don't think I'm gonna get any slack there) so I'm kinda p.o.-ed. I had to leave the project unfinished until I can call Ian at 944 online and give him the old "WTF man?" Maybe I'm missing something. How'd yours go in? Anyone else have this?
The hoses are a major PITA to re-route though - I ended up having to cut out the old "large" line (since it was diagnosed as leaking anyway, I didn't care) the one that goes from the evaporator to the compressor. I found that it was easiest (or should I say least difficult) to route the smaller hose through the firewall from the outside and push the large one out from the inside. I removed the smaller one first to make getting at the big one easier. In Haynes fashion, installation was the opposite of removal. Good deal though - those (%($&(& hoses are in!
Other major problem though: the nice new Sanden compressor doesn't fit!!!
When it hangs on the bracket, in order to swing it over to get the drive belt over it, it bangs against the bracket (limits its movement). The alternator is already at the limit of its movement to provide the most slack and the only other thing that belt goes over is the crank pulley (don't think I'm gonna get any slack there) so I'm kinda p.o.-ed. I had to leave the project unfinished until I can call Ian at 944 online and give him the old "WTF man?" Maybe I'm missing something. How'd yours go in? Anyone else have this?
05-10-2004, 12:22 PM
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Porsche-O-Phile, If I'm reading your post correctly, I think you're a little off on your refrigeration cycle. It goes like this: The compressor creates a high pressure gas thet flows from the discharge side to the dryer and then the condensor where it is changed to a high pressure liquid. It then flows to the expansion valve where it flashes to a low pressure gas and flows through the evaporator picking up the heat in the cabin. It then flows back to the suction side of the compressor as a low pressure gas and the cycle starts again.
