Ricardo Vega

Hey guys, been in Ft L. for about 24 hours and have been having issues with my AC. Was wondering what you guys suggest but first let me tell you my delimmas. So drove into Florida from west Texas and I never had issues with my AC there at all.
So last year I had AC serviced with a friend and had it convert from 12 to 134 and I also did what I had read about bypassing the freeze temp sensor to get lower temps out of it. Had the bypassed for about 15 minutes, as suggested on the listing and had seen temps drop as low as 15 F consistent. No issues at all.
I get to Ft. L. I then started having issues with my AC. I'm assuming it's the moisture building up and clogging up my radiator so it would warm up and then had to shut off for a while so ice build up would go away. Then I would turn on again and would be fine for a while and then shut off again. Finally had my friend that helped me with the AC suggest that it might be low on freon so he recommended to put some in and see.
I also was aware that I had bypassed the freeze temp sensor and so I had also read on another posting to by pass it and connect both terminals together when this happened, so I did that when I pulled over in Orlando and got some 134. Filled up with some and followed instructions to install and since then I get cold air when I start engine for first time but then warms up and I also notice clutch engages way more than before and forced the engine to drop in RPM's by about 200 but it turns on and off way more than before. My brother thinks I have too much air in there and we also noticed on glass being too bubbly and sometimes the bubbles go away but they're there most of the time.
Was wondering what you guys might suggest or think it might be? I'm thinking of taking it to Chucks AC service here in Ft Lauderdale tomorrow but before I do was wondering what you guys would recommend?

Thanks
Ricardo Vega
1987 Porsche 928 S4
120,xxx

raymoni

You do realize that the "freeze temp" sensor is exactly what it says it is. It protects the evaporator coil from freezing when the saturation temperature of the coil drops below freezing (32 degrees). Florida is very humid and your evaporator coil produces a lot of condensate as the cold evaporator coil removes the moisture from the intake air by dropping the temperature of the air as the coil absorbs the heat. if the temp coming out of the vent is 15 degrees then coil saturation temperature is about 0 degrees! At that temperature the coil will freeze up, and since you bypassed the freeze sensor the compressor will not disengage and the coil can freeze solid causing possible cracks in your evaporator, extremely high super heat and liquid refrigerant returning to the compressor and slugging it. Freeze sensor is there for a reason.

At this point I would take your vehicle to a reputable service center and have them hook manifold gauges up. They need to check saturation temperatures, sub cooling and super heat to determine the state of your charge. Bubbles in the sight glass are usually indicative of a low charge. The sight glass is located in the liquid line and should be pure liquid. bubbles typically mean there is vapor present. That in conjunction of a 15 degree temp out of your vent would also lead me to believe you are low on charge.

raymoni

the compressor cycling on and off could be due to a low pressure sensor, or if you got air or moisture (non condensables) in the system you could be cycling on a high pressure safety

Speedtoys

I read this four times, and still dont know what to tell you.


But..I think your problems all route back to here: "temps drop as low as 15 F consistent. No issues at all."

Andre The Giant

I've got the same issue here in Quebec Canada, and I am picking up a temp freeze switch tonight, hoping to fix the issue. I will post the results tonight or tomorrow.

Ricardo Vega

So took my car to Chucks Auto/Air Condition Repair shop here in Ft.L. and hooked up his machine to it. Did diagnostics on my AC and my drier is malfunctioning. Ordered a new one will get in tomorrow and I'll install it and be good to go, I hope.
My doubt is if I should hook it up to the freeze temp sensor or just by pass it for me to get home and not deal with frozen condenser coils. Any suggestions is welcomed. Thanks.

Ricardo Vega
1987 928 S4
120,xxx

dr bob

The drier doesn't suddenly malfunction.

Recommendation: Put gauges on the system and test the running pressures. I'll speculate that the system is overcharged now thanks to the R-134a you've added. the pressure safety switch cycles the compressor off when high-side pressure exceeds about 400 (!!!) PSI. When it does, the compressor stops, and you then start to see bubbles in the sight glass. Have some of the refrigerant recovered, so the low-side pressure is about 30-35 PSI when engine is at 1500 RPM, fan is on speed 2. At 80º ambient that should get you in the ballpark.

In the Florida humidity, you MUST have a working anti-freeze switch in the compressor circuit. Put the leads back on the switch again, so it is working again. With the switch bypassed, you'll very quickly turn the evaporator into a block of ice, blocking airflow. Turn the system off for 20-30 mins, and the ice will slowly thaw and you'll start to get airflow again. The freeze switch should cycle the with vent temps around 40-45º, corresponding to about 35º evaporator surface temp. The surface temps MUST be kept above freezing or the evaporator will condense and freeze the humidity from the air. Florida is different from Texas. You think it was humid in Texas, but Florida is 2x worse. A much larger percentage of system capacity is spent just condensing the extra moisture from the air. It "feels" cooler on the skin since the air is dryer, but also take a lot more to get things actually cold like you might be used to in a dry climate with the freeze protection disabled.

Florida is where you go from Michigan in the winter. It's a hot soggy hell any other time of the year. In my opinion.

Sent from the high desert of central Oregon, the eastern slopes of the Cascades. 4000ft altitude, mid 80's today, about 30% RH. It's abnormally hot and humid here this weekend. Typically 71 with less than 15% humidity. We closed our ski area on Memorial Day. Still plenty of snow, but the mountain bikers want to use the chairlifts.

Ricardo Vega

Dr Bob,

I appreciate your thoughts on this and was wondering why it works perfect for the first 15 minutes, and what I mean perfect is with 45* temps coming out of vents and then it starts to warm up. It never comeback down unless I stop car and restart.
Second thing is if I have bypassed FTS(freeze temp sensor) and put cables back on does it still function from its original specs? The reason I have my doubts about that is because I did have the cables connected back home to the FTS and I had temps of 15 degrees coming out for hours without issues. Wouldn't it make sense to disconnect them from FTS but have them connected to each other?
I maybe have a bad FTS but if I do how do I know that?
My big concern is just having an AC for me to make it back to Texas when I leave in the next few days.

Thanks
Ricardo

dr bob

So you have a system that has evaporator temps well below freezing. The air coming out the vent is somewhere between the incoming air temp and the evaporator temp. You can determine the evaporator temp from the suction-side pressure in the system. Regardless, what you are most probably experiencing is a freeze-up of the condenser. In relatively dry Los Angeles, I could drive maybe an hour at most before I needed to shut the compressor off and let the ice melt. Probably the biggest telltale of the evaporator freezing up was the slow reduction in airflow along with the increase in temperature. The ice reduces air movement through the evaporator until it's almost none. If you recognize that symptom, you have a clue anyway.

The freeze switch needs to be wired in series with the clutch circuit. Reconnect the wires to the switch instead of each other.

The switches do in fact "wear out". The expanding fluid pushes on a brass diaphragm to actuate the electrical part of the switch. The brass work-hardens over time, eventually sticking in one position or the other. You can remove the switch and test it in ice water with your DMM reading continuity through the sitch until the probe temp drops below about 35º or so. The switch should open. When the probe warms up to about 40º, the switch should close again.

raymoni

Correct. A Drier does not "malfunction" I think what he meant to say was that the drier was restricted. The drier is designed to remove any moisture or contaminates in the refrigerant circuit. A full or blocked drier will lead to a restricted liquid line. Symptoms are high head pressure and very low suction pressure. Poorly trained refrigerant technicians usually miss diagnose this as a low charge issue. If you try to add refrigerant to a system with a restricted drier all you will do is increase head pressure, and eventually damage the compressor or circuit....