{"id":1683,"date":"2020-04-06T09:26:46","date_gmt":"2020-04-06T08:26:46","guid":{"rendered":"http:\/\/www.beady.com\/blog\/?p=1683"},"modified":"2024-04-15T13:04:21","modified_gmt":"2024-04-15T12:04:21","slug":"hvac-on-a-p38-with-a-m57-bmw-engine","status":"publish","type":"post","link":"https:\/\/www.beady.com\/blog\/hvac-on-a-p38-with-a-m57-bmw-engine\/","title":{"rendered":"HVAC on a P38 with a M57 BMW engine"},"content":{"rendered":"\n<p>I have been asked about how I got the HVAC working on my P38 Range Rover overland camper ( now officially called Dogger)<\/p>\n\n\n\n<p>Rather just do a reply to the comment I thought I would do a blog post to help you all understand it.<\/p>\n\n\n\n<p><\/p>\n\n\n\n<p>The P38 was at a sweet spot in technology in regards to the amateur converter, why? well, it had very advanced ideas for its time like the uses of a data bus allow remote stations in the doors and keypads but was still not a fully integrated system like what followed in just about every other car.<\/p>\n\n\n\n<p>this means that all the systems can be orphaned with ease, the newer stuff relies on intercommunications between ECU&#8217;s that is hard to reverse engineer and\/or fool<\/p>\n\n\n\n<p>the main systems on the P38 are<\/p>\n\n\n\n<ul>\n<li>BECM + out stations , switch panel, display<\/li>\n\n\n\n<li>Engine ECU<\/li>\n\n\n\n<li>HVAC<\/li>\n\n\n\n<li>gearbox ( if auto)<\/li>\n\n\n\n<li>transfer box<\/li>\n\n\n\n<li>ABS\/TCS<\/li>\n<\/ul>\n\n\n\n<p>I have listed the BECM with the out stations ,doors and display because they communicate on the data bus so are really all one system.<\/p>\n\n\n\n<p>all the others are separate systems that communicate with the BECM via simple wires that are hi\/lo in various configurations, this tells the BECM what&#8217;s happening.  The exception is the later petrol engines which have CAN-BUS data between the gearbox and the engine ECU. in the early cars this is a single wire with a complex waveform.( I may explain that in another post one day)  .<\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"791\" height=\"1024\" src=\"http:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/P38-HVAC-circuit-1995-2-791x1024.png\" alt=\"range rover conversion HVAC wiring campervan and off roader\" class=\"wp-image-1692\" srcset=\"https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/P38-HVAC-circuit-1995-2-791x1024.png 791w, https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/P38-HVAC-circuit-1995-2-232x300.png 232w, https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/P38-HVAC-circuit-1995-2-768x995.png 768w, https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/P38-HVAC-circuit-1995-2-1186x1536.png 1186w, https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/P38-HVAC-circuit-1995-2.png 1203w\" sizes=\"(max-width: 791px) 100vw, 791px\" \/><figcaption class=\"wp-element-caption\">1995 HVAC to engine ECU wiring, 199 on is basically the same but connector C246B is now called C0793<\/figcaption><\/figure>\n\n\n\n<p>The BG wire coming from the HVAC ECU is the request signal, it is asking the engine ECU to have the A\/C compressor on, the engine ECU looks at engine load, temp, and some other things and decides if the extra load of the AC compressor is OK, if it is then it grounds the BS wire, which tells the HVAC unit it is OK to turn on the AC compressor clutch, this wire must be connected on the M57 engine to the original, which should be a thick black\/green wire on the M57 Engine.<\/p>\n\n\n\n<p>The M57 ECU does the control of the AC differently, the HVAC requests the AC compressor if everything is ok then the engine ECU turns on the compressor and sends a signal back to the HVAC that it is on, you can see how more interdependent the later systems are on each other.<\/p>\n\n\n\n<p>here is a list of the reasons the later M57 ECU will not allow the AC compressor on.<\/p>\n\n\n\n<ul>\n<li>Start off status :Road speed &lt; 10km\/h AND accelerator pedal &gt; 60% AND engine speed &lt; 1800 rpm<\/li>\n\n\n\n<li>Acceleration : Accelerator pedal change &gt; 400% \/ second AND engine speed &lt;3000 rpm<\/li>\n\n\n\n<li>Coolant temperature &gt; 117 deg C<\/li>\n\n\n\n<li>Throttle dip : Engine speed &lt; 650 rpm<\/li>\n\n\n\n<li>while starting<\/li>\n\n\n\n<li>Fault code stored in DDE ECU 500 : road speed signal or 120,220 : pedal postion sensor<\/li>\n<\/ul>\n\n\n\n<p><\/p>\n\n\n\n<p>anyhow how to make the p38 work with the M57 DDE4 ECU<\/p>\n\n\n\n<p>simply connect the BS and BG wire on pins 13 &amp; 14 on the HVAC, either C246B or C0793 depending on which year you have. The AC compressor clutch is still controlled by the  C273 BK\/YW wire as normal, you will have to use your brain to turn it off if the car is overheating and use the BM<\/p>\n\n\n\n<p>It is possible to connect up the M57 ECU to work correctly but you will need to get rid of the error code 500 road speed signal which will involve CAN bus speed signal input to the ECU \ud83d\ude41<\/p>\n\n\n\n<p><strong>UPDATE 2024<\/strong>: now we have the cruise working that involved getting the speed over CAN into the ECU this error should disappear. <\/p>\n\n\n\n<p>For the compressor: I used the M57 compressor because of the multi V Aux belt, I made two adapters for the pipes by welding universal fitting from Webasto onto the E46 pipes and then it is easy to clamp the pipe with the clips at home.<\/p>\n\n\n\n<p><\/p>\n\n\n\n<figure class=\"wp-block-image size-large\"><img decoding=\"async\" loading=\"lazy\" width=\"1024\" height=\"915\" src=\"http:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/pipes-for-P38-ac-conversion-1024x915.png\" alt=\"\" class=\"wp-image-1690\" srcset=\"https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/pipes-for-P38-ac-conversion-1024x915.png 1024w, https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/pipes-for-P38-ac-conversion-300x268.png 300w, https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/pipes-for-P38-ac-conversion-768x686.png 768w, https:\/\/www.beady.com\/blog\/wp-content\/uploads\/2020\/04\/pipes-for-P38-ac-conversion.png 1297w\" sizes=\"(max-width: 1024px) 100vw, 1024px\" \/><\/figure>\n\n\n\n<p> all other pipes, and wiring stay the same as original.<\/p>\n\n\n\n<p><strong>Update 2023<\/strong>: I changed the pipe that goes from the compressor to the Condesnor on the front of the radiator to a braided type and for the adapter on the compressor I welded a JIC male fitting to it, this was to add reliability to this pipe, it was vulnerable to damage and hard to fit\/remove.<\/p>\n","protected":false},"excerpt":{"rendered":"<p>I have been asked about how I got the HVAC working on my P38 Range Rover overland camper ( now officially called Dogger) Rather just do a reply to the&#8230;<\/p>\n","protected":false},"author":1,"featured_media":1691,"comment_status":"open","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"footnotes":""},"categories":[5,147,31],"tags":[],"post_folder":[],"_links":{"self":[{"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/posts\/1683"}],"collection":[{"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/comments?post=1683"}],"version-history":[{"count":7,"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/posts\/1683\/revisions"}],"predecessor-version":[{"id":3780,"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/posts\/1683\/revisions\/3780"}],"wp:featuredmedia":[{"embeddable":true,"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/media\/1691"}],"wp:attachment":[{"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/media?parent=1683"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/categories?post=1683"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/tags?post=1683"},{"taxonomy":"post_folder","embeddable":true,"href":"https:\/\/www.beady.com\/blog\/wp-json\/wp\/v2\/post_folder?post=1683"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}