Better aircon clutch relay
04-21-2010, 05:25 PM
#1
Drifting
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Better aircon clutch relay
Last weekend - just as weather in the UK finally warmed up - I had disappointment of ice-cold aircon on trip in the morning, but no cold air on the way back when it was much warmer. Especially disappointing because recently I'd got the hvac working perfectly with new cabin temp sensor, sensor fan motor and new water control valve and connection hose (the water valve was fine, but I like to keep on top of preventive maintenance).
The compressor belt was fine but the clutch was not engaging. With engine off I had almost 12V at the low pressure switch connector with A/C switch in, but if I tried to run even a small 100mA bulb at that point the voltage dived down to about 7V. It looked like failure of the small relay on the PCB in the HVAC head. They are known to fail in a mode where they just can't sustain any decent current at the switched terminals, so the clutch won't engage. It doesn't help that the relay is rated for 2A continuous, and the clutch draws more than this, so the part is almost bound to fail.
Searching posts here it looked like people had been successful in wiring a beefier outboard relay into the board in place of the original (posts referred to a blue original relay), using six wires to the new relay and tucking it somewhere safe in the head.
I was doubly fortunate in having both a yellow relay part number DS2E-M-DC12V, and a GTS-owning friend who is a professional electronics engineer who had found a direct substitute relay which is rated much higher at 5A, by careful checking of the datasheets for various relays.
The replacement relay is available from the UK supplier RS Components. Their stock number is 1782214, and the relay is marked DSP2A-DC12V. It has 6 pins whereas original has 8, but the centre 4 pins of the original are shorted together on each side on the PCB so the replacement has identical functionality. It costs about $9 (they also sell the original relay for about half this price, but it's worth the extra to have a 5A rather than 2A output rating and less chance of future failure)
What's lucky too is that the centre pins of the replacement are spaced differently from the original, but the HVAC board pcb has empty holes on the relevant pcb lands so that the new relay drops in perfectly in the hitherto unused holes! If only all 928 jobs worked out so fortuitously.
I desoldered the old relay with solder pump, and soldered in the new grey one. To be honest I haven't put the controller back in the car yet but this relay works fine in my friend's GTS, so I'm pretty confident it will work fine. Will install tomorrow and report.
So if all works ok this install is far less fiddly than soldering 6 wires to relay pins, soldering them into board and securing outboard relay somewhere in the hvac head.
This only works if you have the yellow original relay, not the blue. There is no drop in replacement for the blue.
Photos show the original yellow relay, and the replacement grey one. All the markings are clear so may be possible to find the grey relay or equivalent in the US?
The compressor belt was fine but the clutch was not engaging. With engine off I had almost 12V at the low pressure switch connector with A/C switch in, but if I tried to run even a small 100mA bulb at that point the voltage dived down to about 7V. It looked like failure of the small relay on the PCB in the HVAC head. They are known to fail in a mode where they just can't sustain any decent current at the switched terminals, so the clutch won't engage. It doesn't help that the relay is rated for 2A continuous, and the clutch draws more than this, so the part is almost bound to fail.
Searching posts here it looked like people had been successful in wiring a beefier outboard relay into the board in place of the original (posts referred to a blue original relay), using six wires to the new relay and tucking it somewhere safe in the head.
I was doubly fortunate in having both a yellow relay part number DS2E-M-DC12V, and a GTS-owning friend who is a professional electronics engineer who had found a direct substitute relay which is rated much higher at 5A, by careful checking of the datasheets for various relays.
The replacement relay is available from the UK supplier RS Components. Their stock number is 1782214, and the relay is marked DSP2A-DC12V. It has 6 pins whereas original has 8, but the centre 4 pins of the original are shorted together on each side on the PCB so the replacement has identical functionality. It costs about $9 (they also sell the original relay for about half this price, but it's worth the extra to have a 5A rather than 2A output rating and less chance of future failure)
What's lucky too is that the centre pins of the replacement are spaced differently from the original, but the HVAC board pcb has empty holes on the relevant pcb lands so that the new relay drops in perfectly in the hitherto unused holes! If only all 928 jobs worked out so fortuitously.
I desoldered the old relay with solder pump, and soldered in the new grey one. To be honest I haven't put the controller back in the car yet but this relay works fine in my friend's GTS, so I'm pretty confident it will work fine. Will install tomorrow and report.
So if all works ok this install is far less fiddly than soldering 6 wires to relay pins, soldering them into board and securing outboard relay somewhere in the hvac head.
This only works if you have the yellow original relay, not the blue. There is no drop in replacement for the blue.
Photos show the original yellow relay, and the replacement grey one. All the markings are clear so may be possible to find the grey relay or equivalent in the US?
04-22-2010, 01:10 AM
#2
If only you had posted this last week! I've just replaced my yellow relay with an out board job. I haven't tested it yet as I'm doing other work.
However, I'm going to order the relay above and maybe change mine back as it is a much neater job.
However, I'm going to order the relay above and maybe change mine back as it is a much neater job.
06-25-2013, 05:04 PM
#4
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Randy--
The contacts on that replacement are rated for 5 Amps AC, just a little less current than the clutch draws and not suitable for long-term use with the inductive DC load. I did the original write-up for the the replacement relay because the only on-board relays I could find were not rated for the actual duty. The full-rated external hang-on relay a) gets the job done with enough spare capacity that you won't worry about it again, and b) is completely hidden in the dash so no external wiring to do. As tempting as that little on-board replacement is, it fails my primary criteria of getting the job done.
The contacts on that replacement are rated for 5 Amps AC, just a little less current than the clutch draws and not suitable for long-term use with the inductive DC load. I did the original write-up for the the replacement relay because the only on-board relays I could find were not rated for the actual duty. The full-rated external hang-on relay a) gets the job done with enough spare capacity that you won't worry about it again, and b) is completely hidden in the dash so no external wiring to do. As tempting as that little on-board replacement is, it fails my primary criteria of getting the job done.
06-25-2013, 05:05 PM
#5
Look here: http://www.mouser.com/ProductDetail/...sfp2R8jqCZIg==
or here: http://www.digikey.com/product-detai...1053-ND/251825
or here: http://www.digikey.com/product-detai...1053-ND/251825
Last edited by pjg; 06-25-2013 at 05:07 PM. Reason: add link
06-26-2013, 01:31 PM
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Randy--
The contacts on that replacement are rated for 5 Amps AC, just a little less current than the clutch draws and not suitable for long-term use with the inductive DC load. I did the original write-up for the the replacement relay because the only on-board relays I could find were not rated for the actual duty. The full-rated external hang-on relay a) gets the job done with enough spare capacity that you won't worry about it again, and b) is completely hidden in the dash so no external wiring to do. As tempting as that little on-board replacement is, it fails my primary criteria of getting the job done.
The contacts on that replacement are rated for 5 Amps AC, just a little less current than the clutch draws and not suitable for long-term use with the inductive DC load. I did the original write-up for the the replacement relay because the only on-board relays I could find were not rated for the actual duty. The full-rated external hang-on relay a) gets the job done with enough spare capacity that you won't worry about it again, and b) is completely hidden in the dash so no external wiring to do. As tempting as that little on-board replacement is, it fails my primary criteria of getting the job done.
06-26-2013, 02:09 PM
#7
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Randy--
If you are comfortable with the soldering tools and such, go for the Dwayne solution. All mods are reversible so long as you don't damage the controller board. If you are a little hesitant about doing the soldering or control head disassembly, send the whole unopene and unmolested controller to Greg and get the mod done for you. Makes it a plug-and-play process.
---
Adding relays in the engine bay, to me anyway, adds another exposed failure point. You get to do a bit of cobbled wiring by the jump post and the 14-pin connector, or you have a separate wire running between the relay and the compressor connection.
I mentioned in your other thread my reservations about amateur work in the CE panel wiring, plus the required documentation and chain-of-custody issues with changes in there.
This is just my opinion, not meant to criticize the efforts or results others have had with the various options available. I like the localized option right at the control head. It may not be the easiest if you DIY, but IMHO it's the cleanest, least invasive and most easily reversible if needed later in the car's life. For those that treasure originality at least as much as functionality (as I do) and see a future market potential for relatively unmolested cars, the heavy-duty relay at the control head makes the most sense for me.
If you are comfortable with the soldering tools and such, go for the Dwayne solution. All mods are reversible so long as you don't damage the controller board. If you are a little hesitant about doing the soldering or control head disassembly, send the whole unopene and unmolested controller to Greg and get the mod done for you. Makes it a plug-and-play process.
---
Adding relays in the engine bay, to me anyway, adds another exposed failure point. You get to do a bit of cobbled wiring by the jump post and the 14-pin connector, or you have a separate wire running between the relay and the compressor connection.
I mentioned in your other thread my reservations about amateur work in the CE panel wiring, plus the required documentation and chain-of-custody issues with changes in there.
This is just my opinion, not meant to criticize the efforts or results others have had with the various options available. I like the localized option right at the control head. It may not be the easiest if you DIY, but IMHO it's the cleanest, least invasive and most easily reversible if needed later in the car's life. For those that treasure originality at least as much as functionality (as I do) and see a future market potential for relatively unmolested cars, the heavy-duty relay at the control head makes the most sense for me.
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06-26-2013, 06:38 PM
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06-26-2013, 08:39 PM
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Randy--
The contacts on that replacement are rated for 5 Amps AC, just a little less current than the clutch draws and not suitable for long-term use with the inductive DC load. I did the original write-up for the the replacement relay because the only on-board relays I could find were not rated for the actual duty. The full-rated external hang-on relay a) gets the job done with enough spare capacity that you won't worry about it again, and b) is completely hidden in the dash so no external wiring to do. As tempting as that little on-board replacement is, it fails my primary criteria of getting the job done.
The contacts on that replacement are rated for 5 Amps AC, just a little less current than the clutch draws and not suitable for long-term use with the inductive DC load. I did the original write-up for the the replacement relay because the only on-board relays I could find were not rated for the actual duty. The full-rated external hang-on relay a) gets the job done with enough spare capacity that you won't worry about it again, and b) is completely hidden in the dash so no external wiring to do. As tempting as that little on-board replacement is, it fails my primary criteria of getting the job done.
06-26-2013, 11:59 PM
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There is no fuse on the circuit. That's the problem. The relay IS the fuse. 
When I do A/C work on a non-operative A/C, I always test the clutch load through the circuit before connecting the clutch to the front main harness. I've always found it to be 3 Amps (unless it was shorted in which case my meter's fuse 10A fuse blows.)
Now that I think about it, it might be more when the compressor is spinning faster. But, if it was much more than 2A the relay in the head would never, ever, last.
When I do A/C work on a non-operative A/C, I always test the clutch load through the circuit before connecting the clutch to the front main harness. I've always found it to be 3 Amps (unless it was shorted in which case my meter's fuse 10A fuse blows.)
Now that I think about it, it might be more when the compressor is spinning faster. But, if it was much more than 2A the relay in the head would never, ever, last.
06-27-2013, 01:23 PM
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I still like the under-hood relay on the early cars. The cooling fan is triggered by coolant temp or refrigerant temp, and I don't feel that the refrigerant temp control works very well.
By using a relay at the right front corner of the engine bay, you can remove the load from the little head relay and have the fan running anytime that the AC compressor is operating - a twofer!
By using a relay at the right front corner of the engine bay, you can remove the load from the little head relay and have the fan running anytime that the AC compressor is operating - a twofer!
06-27-2013, 03:59 PM
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I still like the under-hood relay on the early cars. The cooling fan is triggered by coolant temp or refrigerant temp, and I don't feel that the refrigerant temp control works very well.
By using a relay at the right front corner of the engine bay, you can remove the load from the little head relay and have the fan running anytime that the AC compressor is operating - a twofer!
By using a relay at the right front corner of the engine bay, you can remove the load from the little head relay and have the fan running anytime that the AC compressor is operating - a twofer!
09-11-2013, 03:13 AM
#14
Drifting
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