heater function after a swap - 986 Forum - The Community for Porsche Boxster & Cayman Owners

I deleted the A/C compressor as part of my engine swap. It will eventually go back in at some point. My question is will the heater door and actuators function if the ECM does not receive the signal that the engine is running? I'm using a stand alone ECM so the car thinks it's turned off, and with the A/C pump gone it can't make cold air. The heater coil is circulating as the coil always does, but I get nothing but cold air from the vents regardless of settings.

The AC just gets a signal (voltage) to turn on or off, there is no feedback to anything. There is just 1 wire that goes to the AC. Of course the above is for a car that isn't CAN based. Dont think even a car with CAN will know if it's on or off, but I'm not 100%. also helps to know the year, put it in your signature.

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Apologies. I'm not sure how to put info in the signature line. I see a lot of you have. Mine is an '02 S but not CAN. I'm also very interested in finding a way to feed the tach and hopefully that will let the ECM know something is happening under the bonnet. I'm running the FiTech complete system which has a tach output. I know about the tach adapt but not sure where to tie into the wiring to wake up the tach. Luckily the car "ran" when I got it so the tach is known good.

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The DME has to know that the compressor is on, so it bumps the RPM up at idle to prevent stalling. To Outside's issue, I don't think having the AC compressor in or out should effect your heater functions. I think you're going down the wrong rabbit hole there. Unfortunately, I don't have the knowledge to show you the right path, sorry. https://rennlist.com/forums/924-931-944-951-968-forum/312073-help-ac-compressor-wiring-question.html Scroll down to post #5 for A/C wiring diagram. It looks like as long as the low pressure switch is closed, which yours obviously isn't since there's no freon charge, then voltage is sent to the compressor AND the DME. But again, it should have no effect on your heater functions.

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Neither the engine nor A/C compressor running would have any effect on your heater functions. Except, of course, if the engine is not running your heater core will get no hot coolant, thus no heat. But that's not your case, since your engine is actually running. So, it made me think of a common issue with these cars, and that's the deteriorating foam on the heater baffles. Do you know for a fact that you had heat BEFORE the engine swap? If not, this may be your issue: https://www.youtube.com/watch?v=42IZ0lb33C8

Sorry, didn't phrase that right. yes it will know cause it will turn the AC relay on, which in turn turns the compressor on. What I meant is that the DME doesn't really know (or care) if the compressor turns on or not. it doesn't get anything back from the compressor, it just turns a relay on or off. You can activate the AC but that doesn't mean the DME knows if the compressor is running or not. If in doubt look at your compressor, there is only 1 wire running to it. Like everyone pointed out, it doesn't matter though cause it wont impact heat or not.

First thing you should be focusing on is getting the standalone ECU working with the car and not worry about AC or heat.

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I waited a week for someone else to ask but no luck. What does this have to do with my original question? It runs, it drives, just no hot air from the heater ports when I crank the temp setting up. I can hear the coolant flow in the heater core and the blower runs. Might be the air doors from the sound of things. I'm not sure what you mean by making the stand alone work with the car. The check engine light is on because I'm not sending a run signal to the P-car ECM. Having a working tach would be a bonus but it's not a necessity by any means. I can certainly hear what the engine is doing as it's in my right rear pocket. Any idea how to send the tach signal to the stock unit in the dash via the original harness?

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Did you check my link in post #5? You may be having the common 'foam deteriorating from the baffles' problem. The climate control doesn't care whether the engine (or A/C compressor, for that matter) is on or off, so whether or not it knows is a moot point.

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I did. I believe you may have found the issue. I'll check into it later this week and let you know what I find. Thanks for the link!

3 months later I finally had time to dive into this. I followed the video about how to do the cuts in the air duct, then when I went to tape the front edge down it snapped completely apart. It did give me a bit more access but obviously my plastics are much more brittle than back when the video was made. Once able to see the doors, the foam was completely gone as you guys suspected. I verified function of both air doors and did a quick shop vac clean up then got busy with the metal tape. It took me a couple of hours as access through that hole means you can't see and do at the same time. And of course that tape curls up and has a mind of it's own as to where it wants to stick. All in all I believe it was a success and just in time as fall weather starts this week and heat will be nice to have. Thanks for your help on this!