AC blows warm air

My AC won't work (2010 Boxster S ), but I'm not sure why and need some help troubleshooting. It suddenly stopped working last weekend and just blows warm (ambient) air. If I adjust the temp up, it gets hot; adjust it back and it drops to ambient again, so I think the flapper is working. No condensate drip under the car. Signs thus point to an issue elsewhere causing the AC to not turn on. Refrigerant pressure is about 85psi so I don't think I'm low on refrigerant. The OBDII is reported 27C ambient and 60C intake (hot engine after sitting in my garage an hour). Pressing the AC ON/OFF button and adjusting the fan have no visible impact to the compressor clutch- it appears to be engaged 100% of the time. I took a short video clip. The sound seems abnormal; I'm not 100% sure that it's coming from the compressor, but I think it is. I'd previously thought it was lifter noise. I've been hearing some chirping type noises that I thought were bubbles in the coolant but may be related (dunno). Here's a clip of the compressor: it looks/sounds the same whether the AC is on or not. In this case, it was turned on with the fan off. https://www.youtube.com/watch?v=5AqnrvwsZ-8 Update: skip to post #26 for resolution. This is a clutchless compressor and it turns out that the hub shaft connecting the pulley to the compressor sheared.

85 psi is high for the low side. Did you check the high side ? May be equalized. I worked on a truck 2 weeks ago that did that.[I know, not the same but 85 is high for the low side.] Had to replace the compressor.

Assuming that R134a cycles are common. For that ambient my chart says that the low side pressure should be 45-55 psi. Are you measuring high side? Or with the engine off? The only way you should be able to get high side pressure is with a gauge set. The fittings aren't common. The typical single gauge charging kit fits low side only.

85psi is for the low side with the car running and AC turned on (but blowing warm). Seems consistant with my fear that the compressor is blown internally and spinning but not pumping refrigerant. I saw a post online where someone said 85psi was normal for a Porsche , though that's into the "danger" zone on my R134a gauge. Any idea what's up with the clutch not disengaging?

Low side pressure is about 75psi now, after sitting roughly 2 hours since turning it off. Does the system always run the compressor automatically until pressure builds up, regardless of whether AC is turned on or off?

I think they shut the compressor off with AC off. Don't know if there are any overrides for humidity control but sort of doubt it. It's been a bit to long ago to remember it all but from what I recall for a given refrigerant there are limitations to how much you can vary the pressure and still run the temperatures you want. It would be interesting to know what the high side pressure is. Short of that what's the low side with the system off after its been setting for a while? As to the compressor running continuously my only guess is the clutch seized.

I would check to see if there is any refrigerant in the system. You can do that by hooking to the low side with your gauge after the AC system has been turned off for a few minutes and the engine not running. There is a direct relationship between the refrigerant pressure and its ambient temp as per the chart below. If there is refrigerant in the system your gauge should read some kind of pressure. You will have to try to guesstimate the temp of the refrigerant to get a more accurate assessment. It is easiest to do after the car has been sitting for a while and the whole compartment cools down. The key point is make sure the engine is not running. If your gauge doesn't read any pressure it is a sign that the refrigerant has all leaked out. If that is the case check the front of the car where the condensers are and see if either one has taken a hit by a rock. If the AC quit all of a sudden that is a possibility. The AC systems that I am familiar with usually work as follows. There is a switch on the low pressure side. When the compressor turns on the low pressure keeps dropping until the switch detects a pressure around 25psi. At that time the switch turns off the compressor. This is done to keep the Evaporator form icing up. After the compressor turns off the low side pressure starts to build and go higher. When it hits around 45psi the switch turns the compressor on again and the cycle continues.

Where did you get this chart from? The reason I ask, I would like to know what the definitive numbers that Porsche recommends as far as PSI readings. My compressor is making noise - and I thought it was because the compressor was shot, but it's reading 40psi low / 225 high. Could it be it's undercharged?

As I posted in the OP, low pressure was roughly 85psi with my AC "running" but blowing warm. I took another reading 2hrs later with the car off and it was 75psi. Both readings are consistent with ambient temps today per that chart. Per Porsche 's documentation, the low pressure should always be between 1.4-1.7 which I assume is bar, which is 21-25psi. This does not vary with temperature. High pressure varies with ambient temperature, but I don't have a gauge; would be 200ish psi.

If you had 85 psi running and 75 psi off and somewhat cooled off I suspect your compressor is gone. I'd do a little looking into why before just replacing it. Something else may have failed first. You might try disconnecting the clutch leads or fuse to see if it will disengage. FWIW since Porsche does things differently on any of the systems I've messed with compressor cycling is controlled by the cabin temp set point. This might be biased by a sun sensor and ambient temp. Only time I've seen the low pressure switch come into play is when the system needed recharged.

Pokerpot I got this chart by doing a search on the web "refrigerant temperature pressure". It is a generic chart that shows the relationship between various Refrigerant temperatures and the pressure it exhibits at that temperature. It has nothing to do with any specific automobile specs. It is an easy check when troubleshooting an auto AC problem to try to determine if there is any refrigerant in the system as opposed to completely leaked out and there is none left. It could be useful information knowing that there is no refrigerant in the system. That way you wouldn't waste time trying to figure out if one of the AC components is bad. You would know that you have a leak and you would try to find the leak It sounds like you have a gauge set. So if you hooked up your gauges with the AC off and engine off both gauges would read the same pressure because with the AC off the pressure in the system equalizes. The pressure they read would coincide with the chart based on the the temperature of the Refrigerant. So if you just turned off the engine and the engine compartment is 110 degrees F inside you could assume that the refrigerant temperature is about the same and your gauges should read around 146psi for R134 refrigerant. Having said that, the low/high readings of 40/225psi you reported seem to indicate your compressor is strong @225. Also, a compressor can be noisy and still work fine. One thing that can make a compressor noisy if is you had a real slow leak and have added Refrigerant several times without out adding oil because a little oil leaks out with the refrigerant. I have worked on auto AC's before but on autos other than Porsches. So unfortunately I don't know the exact specs for Porsche . I think most auto AC systems are similar. But you are correct in wanting to know the Porsche specs. Having a gauge set is good. You don't want to just start adding Refrigerant and not be able to monitor the pressures. R134 systems are real finicky and sometimes just a few ounces of the refrigerant makes a big difference. Too much refrigerant and the high pressure can go up too high and that could blow out some seals in the compressor. Based on the readings you reported I think the your system could be undercharged. If the high pressure is 225psi and the low side only pulls down to 40psi it may be because of a slightly undercharged system. The low side really needs to get down in the mid 20's psi to cool well. It could always be something else but most likely a low charge.

Again FWIW the ~2 Bar pressure you've found sounds more like something that would be appropriate for R12 which had lower low side pressures. The only charging info I've found was by weight for an evacuated system. Useless for you.

Just a side note. Any automotive or home AC system will run the evaporator at something over 32deg F. If you go colder than this any water that condenses out will freeze on the coils bringing the whole thing to a halt. Notice where the R134a charging chart pressures places temperature on the chart above. One typically keeps the evaporator below the dew point and above freezing. There will likely be some variation in a specified pressure for a given car due to where the ports are located but this should get you in the ball park. Also since the compressors used are typically positive displacement the inlet pressure has to be high enough to keep the discharge pressure up to where it will condense out at the ambient temp the condenser is running at. A balancing act typical in engineering.

i'm not sure how much of the noise is from the compressor in our cars as there is a cacophony of sounds from the car. but if the noise is from the compressor check the clutch first. a/c system is quite sensitive to the refrigerant pressure, the expert had to top up my gas by 1-2 psi and it was ok again.

You should really get gauges to get low and high side readings. One side just does not give enough info.

I'm going to try to get my hands on a high pressure gauge this weekend.

If it helps any after I got back from a drive today I put a gauge on the low side. With the car off after setting for roughly 15 min the system read 80 psi. Ambient was 71F by the dash display. Starting the car, 987.1CS, and the AC the pressure was 35 psig on the low side. Ambient was still 71F. My chart shows 35 - 40 psi for acceptable low side pressure range for 70F. Just listening the compressor seems to shut off when selecting AC Off. It's more noticeable when switching it back on.

Those are numbers I'd expect for a 134 system. I still think his pressure has equalized, from an internal compressor problem.

Low pressure: 95psi High pressure: 100psi No difference if AC is on or off, or even if the car is on or off. Pretty sure it's the compressor

So, next troubleshooting step, one I should have done three days ago, is I took off the belt and spun the compressor pulley: it spins free. Which indicates the clutch may not be engaged like I thought and the problem may be the clutch (or electronics driving it) after all. Dealer wants $195 for a diagnosis but that may be my best option right now. e: yep, I double-checked and was mistaken before: the clutch is NOT engaging.

There will be a pressure switch in the system that disables the clutch if the refrigerant charge is below a certain pressure (i.e. your refrigerant has leaked out). So it may not be the clutch, but a leak in the system.

The reported pressures are in the ballpark for a R134 system not running. Your video showed the compressor turning. Check and see if you can turn the inside pulley easily by hand. If you can the shaft is sheared and it was just spinning from whatever residual friction was in the clutch when you turned it off. Typically the outside pulley turned by the belt will spin freely but the inside takes some effort. Another thing you could check is if the magnetic clutch is getting power. There should be an electrical connector coming from the compressor. I think it's just 12 V to engage the clutch and maybe a ground. No power when the compressor should be running will give you something else to check.

Actually, my video showed the clutch not spinning- you can see it clearly in the final few seconds that the hex bolt in the middle is stationary. I mistook the rubber cover as part of the clutch, but it's apparently part of the pulley. I checked again and AC on or off makes no different, the hex bolt in the middle doesn't move. The pulley turns easily by hand. I'm hesitant to try to spin the compressor via that one nut. I tried to pull the connector to check and see if it's getting 12V to the clutch, but no joy; I can see the connector, but I just can't get to it. These cars aren't bad for basic PM, but man it's tight for engine repairs!

Good catch. Seems unlikely the frame rate matches pulley speed. No need to try turning it. You most likely have a failed clutch or no power to it. My guess is the latter. If you can't get the connector you might try fuses. Don't recall if you checked already or not.

I took my car into the local dealership today who charged me $195 to drain (and not refill) the refrigerant, and then gave me a quote for $3500 to replace pretty much the entire system!! I said no thanks, got home, and discovered the clutch hub snapped off at the shaft. New one's $70 on ebay, should be here Thursday. Then back to the dealer so they can put the R134a back in. The round piece sitting on my center console? It's supposed to be attached to the broken metal bit sticking out from the compressor shaft. I wasn't expecting the rubber bumpers to fall out and lost one deeper in the engine but managed to fish it out. I was also glad I took this photo because they're not symmetrical. Since my hub was torqued onto the shaft with enough force to shear it in half, it was on there tight . I fought with a combination of ratchet and vice grips for a while without success and eventually got it off using an impact wrench and a 15/16" impact socket that fit fairly tight over the remaining stub. The hub comes off CCW per the standard righty-tighty/lefty-loosey, so set your impact wrench like you're removing lugnuts. On the bright side, I DID get a chance to drive a 718S while I was waiting at the dealership, which is a pretty damned nice car. Plenty of torque at low RPMs, and the exhaust note sounds GREAT from inside the car.

$3500, wow. You know, you can put the 134a in yourself. :cheers:

Yeah, but that's probably $30! I paid $200 to the dealer for the diagnostic which removed all my R134a and I'm going to get my R134a back, dammit, lol. Also, car geeks, this AC compressor (Denso 7SEU17C) does NOT have a clutch, which is part of what was throwing me off during troubleshooting. It has an internal variable wobble plate compressor; the angle of the plate determines compression. Instead of getting 12V on/off, it gets a PWM signal telling the plate what angle (compression) to be at. The hub in the pulley is a mechanical fuse of sorts- it has rubber bumpers to soften the impact, and is designed to shear if the compressor seizes so that the engine can keep running. I don't know why my hub sheared as the compressor seems to spin pretty easy. So, for other people troubleshooting no AC in your Porsche (or Mercedes or other marques that use Denso 7SEU/6SEU clutchless compressors): if you look at your compressor pulley and the 7mm hex shaft in the center isn't spinning, your hub has sheared. Remove the rubber covered retention ring with a screwdriver or pliers (you'll see a gap in the ring in one of the 3 openings.) Turn the 7mm nut CW and the pulley/hub CCW to remove the hub. You can do a web search for "Denso 7SEU" for more detailed tutorials like this one: https://www.youtube.com/watch?v=nLHJ6BadGv8 In my case, I used an impact wrench with a 15/16" socket that fit fairly close to get the remnants of the hub off the shaft; it's going have been wrenched on there TIGHT to shear it so be prepared. Also see if you can figure out WHY it sheared because if your compressor has seized, this was just a symptom and no sense destroying a $60 hub if what you really need is a $300 compressor. In my case, my compressor spun easy with my fingers with the car turned off. Cutaway diagram from Denso's website: http://www.denso-am.eu/media/631294/deac13uk10mm_uk_thermal_ac-compressor_leaflet_web.pdf

Thanks for the info. Makes a lot more sense. I was lost by the original post on the clutch turning all the time. This stuff keeps getting more complex. Some day this will become a problem for someone and this thread will save them a lot of time. :cheers:

thanks for sharing... just curious why they took the R134a out? perhaps to make it easier to replace the compressor, but doesn't it mean that there is less/no oil for the compressor?

Was part of the standard AC service to drain and refill. There's probably some cold hard German logic to it, but damned if I know what it is. And yes, there's less lubrication for the compressor with the R134a drained, but there's also no movement with the hub sheared. To avoid driving around with the compressor running dry, I'm going to have to put the new hub on when I get to the dealer. It'll only take a minute to put it on once I'm there, though (it doesn't need to be tightened, just spun on- the compressor will tighten it the rest of the way while in-use).

Thanks for posting your experience. I'm sure others will find it helpful. On the matter of refilling the 134a yeah you're right to get it back from the dealer, but also I believe it's good to return so they pull a vacuum on the system before adding the 134 back in.

The hub worked, and the AC worked... sort of. The hub worked fine, but the system didn't blow as cold as it should. After a bit of troubleshooting, we found a whole bunch of crud in the line between the drier and expansion valve that we suspect is desiccant from the drier. So, now I get to replace the drier, replace the valve stem (jammed thanks to the crud), purge the line, clean the expansion valve, and dump in a couple cans of R134a . It's going to be over 100 degrees tomorrow again. Not having AC sucks.