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Passenger side vents cold, drivers side warm!?

amodedude1 on Tue June 24, 2014 11:10 PM User is offlineView users profile

Year: 1994
Make: Lexus
Model: LS400
Engine Size: v8
Refrigerant Type: R134a
Ambient Temp: 80
Pressure Low: 15psi
Pressure High: 135psi
Country of Origin: Japan

Hello everyone,

As a disclaimer, this is my first post and I am a complete noob. (despite taking A/C class in tech school) I am attempting to recharge my AC as I am experiencing some issues. The main issue is that the drivers side AC vents are warm but the passenger side vents are always nice and cool. I decided it would be useful to have AC tool on hand and start utilizing what I "learned" in AC shop class so I decided to purchase:

1 - A set of R-134a manifold gauges
2 - An AC vacuum pump
3 - A very accurate AC scale
4 - A 30 pound tank of R134a

My shipment came in today so I started to take some pressure readings:

Static (@ 80degF 60% Humidity): 95 PSI Low , 95 PSIHigh @ Engine off
Dynamic : 15 PSI Low, 135 PSI High @1500rpm

My questions are as follows:

1. Why is my passenger side AC so much colder than the drivers side?
2. My pressures seemed low and I was getting bubbling through the site glass. Since the FSM indicated this was a LOW charge (bubbling @1500rpm) I added 7oz of R134a. Was this a huge mistake and should I have the system EVAC'd and start over so that I can add exactly 2.1lbs of R134a?
3. After an EVAC, will I need to add any oil, or should I just leave the oil alone?
4. Does my static reading indicate contamination in the system, or is this normal? It seems like the pressures were a bit high for 80defF?

Also, I occasionally hear a hissing noise coming from the inside of the dash. Is this related to a low charge, and how so?
Thank you

1994 LS400

Edited: Tue June 24, 2014 at 11:53 PM by amodedude1

Jag987 on Wed June 25, 2014 12:19 AM User is offline

Congratulations on making such a big commitment in doing it right by purchasing a scale and 30 pound bottle of refrigerant! My opinion, a system can be charged to specs this way once you figure out how much remains in the hoses during a recharge, and if will not be much. To answer your questions,
1. The passenger side is likely colder because it is closer to the evaporator. Sounds strange, but unless this is a duel zone system, it is often true.
2. With R135a, the bubbles do not mean much, on a R12 system they could be an indication of low charge. By the pressure reading of 15/135 @ 80*, I would believe it has a low charge. However, without evacuating the system, anything that is added is just a guess. I am not saying I never "guess" and go off readings, but experience helps here. Given the age and other factors, I would evac and start with an empty system.
3. Unless the evac system has an oil collection system and it draws a bunch out, I would add an ounce, if any. But again, without flushing the system and draining the compressor, anything added (or left alone) is just a guess.
4. IMHO, static pressure is only good to show the system is holding pressure and there is some refrigerant in the system. Yes, I know there are pressure/temperature charts that show what it should be, but I still don't give them a lot of credit, just another tool in the bag.

Evac, add some dye, recharge and let us know what it does. Welcome to the forum!

I bought a can of 134a at w**-mart that had a stop leak, oil, and dye in it. It also had a hose and a gauge, so now I'm an AC pro!

mk378 on Wed June 25, 2014 9:10 AM User is offline

Does it work better now? It is OK to "top off" an old car that may have simply leaked out very slowly. If performance is still poor though the next step is to recover and charge by weight before trying to diagnose further. That removes the charge amount as a possible problem.

Static pressure should match the temperature scale on the inner part of the low side gauge dial. This is the only time you use that scale. Of course car temperature isn't likely to match air temperature unless the car has been sitting in a constant temperature garage for a long time. Static pressure higher than expected does suggest there is air contamination. Static pressure lower than expected means that the refrigerant is nearly all gone.

Hissing noise in the evaporator area is refrigerant flow through the expansion valve. It is sometimes normal but it does tend to get worse when undercharged and you don't have a steady solid flow of liquid.

wptski on Wed June 25, 2014 9:15 AM User is offline

A R134A pressure temperature chart shows at 80F the pressure should be 86.7psi. Was the engine cold or at ambient temperature? If it was, you have air in the system.

amodedude1 on Wed June 25, 2014 1:10 PM User is offlineView users profile

When I took the static reading, the car had been sitting in my driveway after the commute home from work for about an hour or two, so I suppose the engine bay could have been ever so slightly warm.

I gave the AC a try this morning and I nearly froze into a Popsicle on my way to work. The outside temperature (as stated by my cars outside air temp readout) was 76degF. I will give it another try today after work and see how it does. Today's high should be around 83defF so we'll see how it does then. So far so good!

Both driver and passenger side vent temps were equivalent so far as I could tell and I did not hear anymore hissing noise.

For peace of mind, I would like to bring it over to a shop and have them EVAC the system so I can refill to the proper capacity.

If I decide to do this, should I add a bit of oil to the system?
How much should I add?

Or should I just flush the system with my air compressor and the flush tool you can rent from auto zone (after the EVAC of course)?
Is this overkill?

... P.S. - the car is 20 years old, so I think the low r134a level was simply due to very slow leakage over time. IMO

1994 LS400

Edited: Wed June 25, 2014 at 1:11 PM by amodedude1

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