R-12 to R-134a A/C Swap
08-15-2013, 03:56 AM
#1
R-12 to R-134a A/C Swap
I will post this as someone was interested in doing this swap, and it would be best to post it here so everyone interested can see what it takes.
When the A/C system on my Maxima went and since getting a hold of R-12 Freon is practically impossible, I decided to go with a R-134a A/C swap from 93/94 Maxima. Yeah, one could have done a "retrofit", but I wouldn't take the risk of something going bad because one used a type of refrigerant on a system that wasn't designed for it.
Hardware
To do the swap, you will need all the hardware that the refrigerant touches since all the mentioned parts differ from the R-12 components. Mounting all of the hardware is simply bolt-on, no modifications needed. I will get to the electrical modifications in a bit.
-Compressor and its engine harness connector pigtail
-Condenser
-Evaporator assembly (with the thermo control amp - very important!)
-Pigtail for the thermo control amp. Get plenty of wiring from the amp connector as you will need all of it to reach to the climate control harness.
-Lines and hoses
-Drier (A.K.A. liquid tank). Get this item as new as it acts as a filtration system.
-Dual pressure switch on the drier and its engine harness connector pigtail. You can re-use the switch from the donor Max if it's still good.
-New O-rings
A note for 89-91 owners: Nissan revised the low pressure A/C hose and power steering cooling design starting with the 92 models. I'm mentioning this because the low pressure A/C hose's new path interferes with the power steering suction hose of the 89-91 models. You would still be able to install everything and get the new A/C working, but it can get frustrating when working around that area. So while you're getting parts from the donor, I would also recommend getting the later version power steering reservoir, suction hose and the hose going from the reservoir to the cooler line. Me, for some reason, not only changed those parts but I also changed the cooler line to the shorter 93?/94 version. I will try to get a picture of the two different A/C hose designs when I can.
I would also recommend getting new Schrader valve cores for the low and high pressure hoses to make sure refrigerant doesn't leak out of the ports. Nissan should have them (P/N J2138-89910). If the donor Maxima doesn't have the service port caps you can also get them from Nissan (Low: J2136-89910, High: J2137-89910).
I'm not sure if the A/C system from a VE Maxima could work on a VG Maxima, the only issue I see is if the mounting points of the compressor is different from a VG Maxima. But just to be safe, stick to a GXE. If someone was able to successfully transfer the A/C parts from a VE Max to a VG Max, let us know!
Here's a picture of the R-12 and R-134a evaporators, with the R-134a type having the thermo control amp. Make sure you get the amp! Also, make sure the amp is placed in the middle of the evaporator core (there's a TSB in regards to the placement and James92SE can attest to that!
)
Wiring
For the wiring, replace the connectors of the compressor and dual pressure switch by cutting and soldering. Here's an example with the compressor connector.
Thermo Control Amp
Yup, it has its own section because it's a very important part of the R-134a system. On the R-12 system, there is a suction throttling valve that would regulate Freon flow and prevents the evaporator from freezing. On the R-134a system, that part is removed and instead uses a thermo control amp to electronically monitor the A/C temperature coming from the evaporator and turns off the compressor when it gets too cold. If you were to swap out the parts but don't wire the amp, the evaporator will freeze the condensation passing through and eventually it becomes a giant ice cube that blocks airflow.
On the climate control harness, look for these two wires. White/blue is ignition power and light-green/black is the A/C enable signal. I will get a better pic soon, but the wiring diagram would do for now.
For the white/blue wire on the thermo control amp connector, use a quick splice connector to tap into the power for the climate control. For the A/C signal, you will need to cut the light-green/black wire on the climate control harness. Leave enough room from the climate control connector. Then join the cut wire from the connector side to the pink wire of the thermo amp connector and join the pink/black wire from the thermo amp to the other cut section of the wire.
Once it's wired up, test it to make sure that the compressor turns off when the A/C gets cold enough to shut it down. The compressor will turn back on when the reading temp goes up.
And that's it! You now got up to date air conditioning that can be easily serviced!
Also, I don't think it needs to be done but I did it since it was of no use anymore. On the front of the condenser by the horns, there is an ambient temperature switch that would also shut off the A/C when outside temp is too cold. I just removed it and bypassed it.
When the A/C system on my Maxima went and since getting a hold of R-12 Freon is practically impossible, I decided to go with a R-134a A/C swap from 93/94 Maxima. Yeah, one could have done a "retrofit", but I wouldn't take the risk of something going bad because one used a type of refrigerant on a system that wasn't designed for it.
Hardware
To do the swap, you will need all the hardware that the refrigerant touches since all the mentioned parts differ from the R-12 components. Mounting all of the hardware is simply bolt-on, no modifications needed. I will get to the electrical modifications in a bit.
-Compressor and its engine harness connector pigtail
-Condenser
-Evaporator assembly (with the thermo control amp - very important!)
-Pigtail for the thermo control amp. Get plenty of wiring from the amp connector as you will need all of it to reach to the climate control harness.
-Lines and hoses
-Drier (A.K.A. liquid tank). Get this item as new as it acts as a filtration system.
-Dual pressure switch on the drier and its engine harness connector pigtail. You can re-use the switch from the donor Max if it's still good.
-New O-rings
A note for 89-91 owners: Nissan revised the low pressure A/C hose and power steering cooling design starting with the 92 models. I'm mentioning this because the low pressure A/C hose's new path interferes with the power steering suction hose of the 89-91 models. You would still be able to install everything and get the new A/C working, but it can get frustrating when working around that area. So while you're getting parts from the donor, I would also recommend getting the later version power steering reservoir, suction hose and the hose going from the reservoir to the cooler line. Me, for some reason, not only changed those parts but I also changed the cooler line to the shorter 93?/94 version. I will try to get a picture of the two different A/C hose designs when I can.
I would also recommend getting new Schrader valve cores for the low and high pressure hoses to make sure refrigerant doesn't leak out of the ports. Nissan should have them (P/N J2138-89910). If the donor Maxima doesn't have the service port caps you can also get them from Nissan (Low: J2136-89910, High: J2137-89910).
I'm not sure if the A/C system from a VE Maxima could work on a VG Maxima, the only issue I see is if the mounting points of the compressor is different from a VG Maxima. But just to be safe, stick to a GXE. If someone was able to successfully transfer the A/C parts from a VE Max to a VG Max, let us know!
Here's a picture of the R-12 and R-134a evaporators, with the R-134a type having the thermo control amp. Make sure you get the amp! Also, make sure the amp is placed in the middle of the evaporator core (there's a TSB in regards to the placement and James92SE can attest to that!
)Wiring
For the wiring, replace the connectors of the compressor and dual pressure switch by cutting and soldering. Here's an example with the compressor connector.
Thermo Control Amp
Yup, it has its own section because it's a very important part of the R-134a system. On the R-12 system, there is a suction throttling valve that would regulate Freon flow and prevents the evaporator from freezing. On the R-134a system, that part is removed and instead uses a thermo control amp to electronically monitor the A/C temperature coming from the evaporator and turns off the compressor when it gets too cold. If you were to swap out the parts but don't wire the amp, the evaporator will freeze the condensation passing through and eventually it becomes a giant ice cube that blocks airflow.
On the climate control harness, look for these two wires. White/blue is ignition power and light-green/black is the A/C enable signal. I will get a better pic soon, but the wiring diagram would do for now.
For the white/blue wire on the thermo control amp connector, use a quick splice connector to tap into the power for the climate control. For the A/C signal, you will need to cut the light-green/black wire on the climate control harness. Leave enough room from the climate control connector. Then join the cut wire from the connector side to the pink wire of the thermo amp connector and join the pink/black wire from the thermo amp to the other cut section of the wire.
Once it's wired up, test it to make sure that the compressor turns off when the A/C gets cold enough to shut it down. The compressor will turn back on when the reading temp goes up.
And that's it! You now got up to date air conditioning that can be easily serviced!
Also, I don't think it needs to be done but I did it since it was of no use anymore. On the front of the condenser by the horns, there is an ambient temperature switch that would also shut off the A/C when outside temp is too cold. I just removed it and bypassed it.
Last edited by jbbons25; 02-15-2014 at 12:20 AM. Reason: Updating stuff as I remember from my progress
01-25-2014, 04:23 PM
#4
That is a very informative writeup. I didn't do a swap however i just changed my high and low pressure fittings and put in a new condensor then had the system properly vacumed and charged with the 134a other than that that was it but that was about 4 yrs ago and it's been blowing ice cold air ever since with absolutely no issues incase anyone's curious to know how the stock system holds up to 134a.
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