So first day really driving this thing and noticed that when the air conditioning is on that sometimes I can hear a hissing sound that is intermittent with a throttle surge. The hissing comes from the center vent or maybe lower, could be the evaporator... not sure. The car was converted to R134 per the importing dealership. The air con is cold but I don't know if it is leaking and going to start not being cold.... anyone else have this issue before?

Thanks.

 

The evaporator is under the dash/behind the glove box on your passenger side. That's the only part of the system that sees refrigerant inside the car. It is pretty easy to replace but requires the system to be emptied.

Not sure if that's where your sound is coming from, try to get a video/sound clip of the noise and that may help.

 

The expansion valve under the dash will make a hissing sound sometimes. Could also be some air in the system, they may not have done the best job in the 134a conversion.

If the refrigerant was leaking and was enough to have a hissing sound it would be empty already. There's not much refrigerant in an AC system.

The surging may be when the compressor is kicking off and the idle isn't compensating properly.

Dale

 

If a leak is big enough to hear, your AC wouldn't work... so it's not a freon leak. It is probably the expansion valve cycling and letting refrigerant going thru it. Your throttle surge is something else, but it would cause the compressor rpm to raise and pump more freon.

Hope they used the right oil in the conversion and didn't just swap out R12 for R134.

Only real way to check if you are low is to check the static and hi/lo running pressures.

 

The conversion was done over in Japan. I have the Japanese service records. But the surging/hissing occurs while driving, not at idle. It is such a weird feeling because I can feel a power sap going on when it happens.

I've also heard that the Japanese batteries suck... and can cause load issues. Don't know how much truth there is to that. Only thing I can do if it doesn't stop is take it to a/c shop and have them suck the 134a out, do a vacuum test, and then refill with proper oil and more 134a.

 

The only thing I can think of being related between the throttle surge and the a/c... On the evaporator, there's a thermosensor. It keeps the evaporator from icing up by cycling the compressor. The circuit that locks your compressor clutch on and turns the "condenser" fans on goes through that sensor.

Maybe the throttle surge you're describing is the clutch unlocking under throttle. Still not sure what the noise could be. Having the system emptied and refilled properly may be a good idea.

 

AC is kind of voodoo work sometimes.

Many times with a 134a conversion they end up over-charging the system with refrigerant to get the temps lower. 134a doesn't cool as well as R12 in an R12 system. The higher charge means more load on the compressor, which means more load on the engine, which means you can feel the compressor engage and disengage driving around.

Also possible they didn't properly change out the oil and everything in the process. That can cause weirdness as well.

A proper 134a conversion in an FD will get cool, but not cold. Like 45 deg. air out of the vents instead of 34 degree air. It's not a big deal if you live up north, but in Pcity with high temps and high humidity it isn't great.

You may want to look into covering to R-152a, the keyboard dust-off. You have to do it yourself as a shop won't do it for you. It's very similar to R12 and can give similar performance.

Dale

 

Drove it today and the air con was cold.... and then it started not being so cold. I‘m not sure if there is a leak or not, or if it’s a recharge issue. Either way, in a week or so bringing it in to vacuum it out, do a vacuum test and refill with proper oil and refrigerant and go from there.

Also tomorrow I plan to check the drier for any bubbles etc per the shop manual.

 

If you have a PowerFC it's common to have problems with the AC not turning on with fan speeds 3 and 4. Mine's doing that now and I need to fix it.

You can wire in a relay to solve the problem.

In other words make sure it's the refrigerant and not an electrical issue.

Dale

 

Still running stock ECU (as far as I know). Looking to upgrade to a PowerFC soon.

 

So quick update because I hate when threads start with a problem and die without a resolution...

Took car into the AC shop and the tech and I worked through it. The system appeared to have too much r134a in it when we evacuated the system. After a vacuum test determining no leaks, went ahead and started to refill the system with the r134a.

However, putting the 1.2lbs in the system was not enough and we tried upping it a little bit. We upped too much and again ran into problems while watching the gauges... so we evacuated the system and started over. This time we took a measured approach and slowly added refrigerant into the system until we got the low and high sides to hold the correct pressures. At the end we ended with a little over the 1.2lbs... how much exactly I couldn't tell you unless we re-evacuated the system. Now the a/c blows nice and cold even at idle on a 95F degree Florida day with 100% humidity.

The surging also stopped.

However, like all things with an FD, I'll drive it around for a month or so and report back if any issues come back up or remain unresolved.

 

So to update this... the issue didn't go away.. the surging and hissing did...

However, turned out it was a bad expansion valve that I needed to replace. AC is now super cold and no further issues after few months since the fix!