Checking the Air Conditioning and R-134a Retrofit

Jonas McMillan writes:

Has anyone with an S13 recently gotten their air conditioning recharged. I have a '92 and the a/c is starting to weaken a bit. I'm also getting a little paranoid about the whole freon recharge thing. Have the prices become totally unreasonable? How much was the


Are there any options for retrofitting cfc-free systems? Thanks for your help!


Hi Jonas-

When you say "weaken", what do you mean? Do you have a thermometer? Measure the air temp coming out of the vents and then the temp at the blower assembly inlet. (By the passenger footwell). At 86 deg. F and the outside humidity at 50 - 60 %, your vent temp should be 50 -54 deg. F. As the humidity and inlet air temp go up, the outlet temps will also.

A bit more thorough method:

Our beloved's that have A/C are equipped with a receiver drier that has a sight glass on top of it. This is pretty easy to find. Stand in front of the car by the battery. Look just to the right, next to the radiator is the receiver drier. It has the small un-insulated

refrigerant line going in and out of it. The sight glass is on top and not very big. You may need to wipe the glass off to see through it.

Looking in the sight glass with the A/C running will give an indication of the amount of refrigerant in the system. There are 4- conditions that can be determined by looking in the glass and feeling the temperature of the refrigerant lines.

To check this out: Turn the A/C on and have the Temperature Selector all the way COLD. Make sure all the doors and windows are closed. The Fan switch should be at the maximum speed and the Rec switch set to recirculate the air. Have the air set to come out of the dash vents.

Look into the sight glass and determine the refrigerant charge amount:


For all practical purposes, don't concern yourself with the temperature of the refrigerant lines. If you see bubbles and you're not getting nice cold air, the system is low on refrigerant. If there are not any bubbles and it's making cold air, you're OK!

The high-pressure refrigerant line is the small un-insulated one. The low-pressure line is the bigger insulated one. Check their temperature as they go through the firewall on the right (passenger) side of the car.



Adequate Charge:

It is clear in the sight glass. The high pressure side is HOT and the low pressure side is COLD. There is big difference in temperature between the high and low-pressure lines. (Air bubbles sometimes increase when engine speed is increased or decreased)


Insufficient Charge:

In the sight glass it looks foamy or bubbly. Air bubbles always appear. The high pressure side is WARM and the low pressure side is SLIGHTLY COLD. There is no large difference in temperature between the high and low-pressure lines.


Almost No Refrigerant:

Frost appears in the sight glass and there is NO temperature difference between the high and low side.


Too Much Refrigerant:

No foam or bubbles can be seen in the sight glass. The high pressure side is HOT and the low pressure side is SLIGHTLY WARM. There is a small difference in temperature between the high and low side.


Note: A reminder that the system is under pressure and the refrigerant used

can cause FROSTBITE to whatever it touches!

Be careful of the engine fan also!

The reasons for the condition of your refrigerant charge can vary. Over time, the flexible connections of the refrigerant lines may seep a little refrigerant. At 140k miles, our system hasn't needed any A/C service. If the system is low, you may have a leak. See the FAQ about A/C Leak Check.

If you've just had the system serviced, they might have either over-charged your refrigerant level or not put enough in. Lastly, run the A/C at least a few minutes each month to keep the flexible connections from "drying out". There is oil in the system along with the refrigerant and this will be circulated to keep everything in good shape.



As for retro-fitting to R-134a, this has been a quest of ours for a few months.

Your '92 has R-12 as the refrigerant. As it contains CFCs (Chloro Floro Carbons), it is no longer being mfg.'d (legally). When you go to the local A/C mechanic, they are gonna get ya' for this refrigerant being in short supply. We were quoted $40 / lb. the other day. Luckily, our system only hold about 2 lbs.

Your options are to keep the R-12 system or get a retro-fit to R-134a. R-134a is less efficient of a refrigerant than good ol' R-12, but it is environmentally friendlier. We asked at the dealer if a retro-fit kit was available for our '91 and the Svc. Mgr. said that he hasn't a kit for ANY Nissan! Right now, they are just repairing the system and recharging with R-12. He asked that we let him know what we find for parts to do the retro.

At Pep-Boys, Castrol has a kit to make this change. It is a different oil for the compressor and adapters for the service ports. Since the refrigerants need to be segregated, the R-134a systems have their own special ports! Theoretically, all one has to do is recover all of the R-12 (Special machine needed to do this), pump all of the oil out, flush the system w/ an inert gas like nitrogen, fill compressor back up w/ the new oil, evacuate the air and moisture out, and add the R-134a. Sounds worse than it really is!

Our concerns are two-fold. One, we have an understanding that the expansion valve in the evaporator may to be changed. This will properly meter the R-134a to help keeps it's efficiency up. We're trying to verify this. Second, while researching this issue, we've came across a debate about the toxicity of R-134a. While R-12 isn't healthful, it's been said that R-134a is deadly. The jury is still out w/ us. We can't say for sure. We haven't heard of any deaths from this. And you KNOW it would have made the news!!

Let us know what you find and do about all of this. We'll do the same.



'91 s13

Another Tip

Try checking the compressor fan, the little fan in the front of the radiator. I have a 90 240, and the air works after a while, but has lotls of trouble on real hot days. The fan motor is burnt out on mine, and that is the problem. the part os about $140 through a dealer.

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