W114 / W115 - Retrofitted new Sanden A/C but won't turn on - Page 2 - Mercedes-Benz Forum

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post #11 of 26 (permalink) Old 07-24-2015, 10:51 AM
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Why not test your connections with a voltmeter? Test the input for the A/C unit and the switch. Like TZ_280SEL said it could just be that the switch is really old and fails to provide power to the unit.
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post #12 of 26 (permalink) Old 07-24-2015, 03:04 PM
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On the W114/115 cars starting about 1970, The AC power/thermostat control on the center console has both an electrical switch/thermostat for the compressor clutch and a vacuum valve for airflow and blower selection.
The engine needs to be running for the vacuum.
When you turn the control to the AC position, A vacuum pod above the accelerator pedal operates a flap in the ducts to switch airflow from heater to AC, and move the change-over switch, also located above the accelerator pedal, to switch power from the heat/fresh-air blower to the AC blower. There should be an aux fusebox underhood, perhaps near the firewall, with two fuses for the AC. On my '72 250, there's no pressure-switch in the AC system. Nor one shown in my FSM wiring diagram. Only a temperature switch on the filter-drier for the aux fan.
Hope this helps.

Happy Motoring, Mark

Last edited by Mark DiSilvestro; 07-24-2015 at 03:10 PM.
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post #13 of 26 (permalink) Old 07-26-2015, 12:57 PM Thread Starter
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@Kaelor , I did just finally get an opportunity to step out into the garage with my test lead and all the fuses checked out. An interesting thing occurred:

1. As I used the probe to test the two electrical leads that are connected to the A/C temperature switch (screwed into the top of the A/C dryer unit - top of photo - attached to the firewall). On the prong closest to the firewall, when I touched it with the test lead, lo and behold, the always-dead condenser fan sprang to life! The outside lead did nothing.

2. With the ignition on - but the engine off - I took the test lead and contacted the two connections on the back of the fan control switch on the console. That yielded no results other than a faint smell of cooking electronics. I didn't do anything other than use the probe to touch one prong and then the other. Not sure why it would smolder that way but it certainly cannot be good.

3. With the ignition on but the engine off, I touched the hot connection to the compressor with the test probe and it was completely dead. That is probably how it should be but I wanted to share this in case it means something.

I'm handy in many areas but wiring is something I'm just starting to learn about. After watching some instructionals on YouTube, I am starting to develop an understanding but I know I'm missing some higher understanding. Hope this info I've just shared helps to shed some light on this problem and with any luck, means something to those of you who better understand the electricals on these fine old cars.

@Mark DiSilvestro , Later this evening I should have a chance to get back out in the garage and try the vacuum pod test you suggested. I tried to move the lever with my hand and that thing would not budge even a bit. Is it true that if that switch doesn't completely close, the air is never going to turn on? I hope it is just the 3 speed fan switch that is the problem. The car is low miles and everything beneath the dash looks so pristine. Hope springs eternal.

Thanks for all your help, guys!

Last edited by Dave5928; 07-26-2015 at 11:13 PM. Reason: updated info
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post #14 of 26 (permalink) Old 07-27-2015, 05:16 AM
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Quote:
Originally Posted by Dave5928 View Post
@Kaelor , I did just finally get an opportunity to step out into the garage with my test lead and all the fuses checked out. An interesting thing occurred:

1. As I used the probe to test the two electrical leads that are connected to the A/C temperature switch (screwed into the top of the A/C dryer unit - top of photo - attached to the firewall). On the prong closest to the firewall, when I touched it with the test lead, lo and behold, the always-dead condenser fan sprang to life! The outside lead did nothing.

2. With the ignition on - but the engine off - I took the test lead and contacted the two connections on the back of the fan control switch on the console. That yielded no results other than a faint smell of cooking electronics. I didn't do anything other than use the probe to touch one prong and then the other. Not sure why it would smolder that way but it certainly cannot be good.

3. With the ignition on but the engine off, I touched the hot connection to the compressor with the test probe and it was completely dead. That is probably how it should be but I wanted to share this in case it means something.

I'm handy in many areas but wiring is something I'm just starting to learn about. After watching some instructionals on YouTube, I am starting to develop an understanding but I know I'm missing some higher understanding. Hope this info I've just shared helps to shed some light on this problem and with any luck, means something to those of you who better understand the electricals on these fine old cars.

@Mark DiSilvestro , Later this evening I should have a chance to get back out in the garage and try the vacuum pod test you suggested. I tried to move the lever with my hand and that thing would not budge even a bit. Is it true that if that switch doesn't completely close, the air is never going to turn on? I hope it is just the 3 speed fan switch that is the problem. The car is low miles and everything beneath the dash looks so pristine. Hope springs eternal.

Thanks for all your help, guys!
The rectangular metal object in your second photo is your AC thermostat. It only operates the compressor - not the fans. The only fan switch is the round knob in the middle of the sliding heater controls. First, does your fan switch operate the heater-fan? If so, at least your fan switch and that part of the change-over switch above the accelerator-pedal is working.
I don't have the FSM wiring diagrams with me right now. But I don't believe the change-over switch operates the AC compressor.

What type of probe are you using? One with a 12-volt lamp and cable with alligator-clip shouldn't have caused any electrical smell unless you bridged across the two green wires and there's a short in the compressor wiring, or you grounded the probe against something.

There's an alloy vacuum control-valve connected to a pair of vacuum lines, attached between the AC thermostat and the console. That operates the vacuum pod above the accelerator to switch the air-flap, and the change-over switch to move the circuit from heater-fan to AC-fan. You may need to pull the console further out to disconnect & check the vacuum-lines at the valve.
With the engine running, see which line has vacuum. If there's no vacuum, you'll need to track that down. If there's vacuum to the valve, rotate the knob from one extreme to the other and check if there's vacuum through the valve, or from the valve to the pod. This should get you started. Good luck.

Happy Motoring, Mark

Last edited by Mark DiSilvestro; 07-27-2015 at 05:26 AM.
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post #15 of 26 (permalink) Old 07-27-2015, 06:37 AM Thread Starter
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Thanks so much for the detailed response, @Mark DiSilvestro
Quote:
Originally Posted by Mark DiSilvestro View Post
First, does your fan switch operate the heater-fan? If so, at least your fan switch and that part of the change-over switch above the accelerator-pedal is working.
I don't have the FSM wiring diagrams with me right now. But I don't believe the change-over switch operates the AC compressor.
Both heat and A/C fans are dead and have never worked in the year that I've owned this car.

Quote:
Originally Posted by Mark DiSilvestro View Post
What type of probe are you using? One with a 12-volt lamp and cable with alligator-clip shouldn't have caused any electrical smell unless you bridged across the two green wires and there's a short in the compressor wiring, or you grounded the probe against something.
I was using the basic 12v probe w/ the alligator clip. I must've somehow bridged something but with such a small point, it would seem difficult to do (but trust me, I'm 'good' like that). Will be more careful.

Quote:
Originally Posted by Mark DiSilvestro View Post
There's an alloy vacuum control-valve connected to a pair of vacuum lines, attached between the AC thermostat and the console. That operates the vacuum pod above the accelerator to switch the air-flap, and the change-over switch to move the circuit from heater-fan to AC-fan. You may need to pull the console further out to disconnect & check the vacuum-lines at the valve.
Vacuum lines are one of those mysterious, scary objects I've avoided up till now. Will have to look up how to test them and go for it. In this Tampa heat, let's just say I'm HIGHLY motivated to find a solution to this problem. This is a daily driver car.

Quote:
Originally Posted by Mark DiSilvestro View Post
With the engine running, see which line has vacuum. If there's no vacuum, you'll need to track that down. If there's vacuum to the valve, rotate the knob from one extreme to the other and check if there's vacuum through the valve, or from the valve to the pod.
With the engine running, I didn't see any movement with that vacuum pod above the gas pedal. Time to bone up on my vacuum line testing abilities. Is it true that without the vacuum pod fully operational that the A/C system as well as the fan will not operate at all?

I very much appreciate your gift of knowledge. I'm no dummy but these cars' HVAC systems require some special understanding that isn't exactly intuitive at first blush. Happy Monday!
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post #16 of 26 (permalink) Old 07-27-2015, 11:44 AM
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Quote:
Originally Posted by Dave5928 View Post
Thanks so much for the detailed response, @Mark DiSilvestro

(quote) Both heat and A/C fans are dead and have never worked in the year that I've owned this car. (quote)

Usually the change-over switch will stop at one end or the other after the engine is shut off. So the fact that BOTH fans aren't working could be bad news. If the heater fan itself is bad, pulling the console, heater & AC system to replace it is a two-day job. But for now, the AC fan is just inside the console so that should be much easier to deal with.


(quote) I was using the basic 12v probe w/ the alligator clip. I must've somehow bridged something but with such a small point, it would seem difficult to do (but trust me, I'm 'good' like that). Will be more careful.
Vacuum lines are one of those mysterious, scary objects I've avoided up till now. Will have to look up how to test them and go for it. In this Tampa heat, let's just say I'm HIGHLY motivated to find a solution to this problem. This is a daily driver car. (quote)

Mysterious maybe.
For the newbie DYI-er, I would think wiring would be much more scary. I never heard of vacuum lines causing a fire.


(Quote) With the engine running, I didn't see any movement with that vacuum pod above the gas pedal. Time to bone up on my vacuum line testing abilities. [B]Is it true that without the vacuum pod fully operational that the A/C system as well as the fan will not operate at all? (quote)


With the vacuum lines disconnected from the control-valve, and the engine running, you may be able to feel some 'sucking' from one of those lines with your finger. If there's no vacuum, your best bet is to look underhood for any vacuum lines that go to/through the firewall to see if any are broken or disconnected. Even without vacuum, You probably could get the AC compressor running. But lack of vacuum can disable the AC blower and block it's airflow.

(quote) I very much appreciate your gift of knowledge. I'm no dummy but these cars' HVAC systems require some special understanding that isn't exactly intuitive at first blush. Happy Monday!
I've had a '72 W114 220 and '72 W115 250 sedan. Both needed significant rehab to get the AC working. Though those cars were much younger 25 years ago and their change-over systems were still working.
My 250 also needed a new heater-fan and I replaced one on a friend's '72 220 more recently. Hence my two-day estimate to pull everything apart on the first day. Then get everything back together on the second.
At least the entire dash doesn't need to come out for this job.

Happy Motoring, Mark

Last edited by Mark DiSilvestro; 07-27-2015 at 11:51 AM.
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post #17 of 26 (permalink) Old 07-27-2015, 06:27 PM
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Alright guys, I could really use your help! I just spent the last week carefully removing the old factory A/C lines and York compressor, refitting the system with new lines and a rotary Sanden SD5H compressor. I'm no dummy but I can say I've never attempted A/C work before now. I took my time and ensured each and every fitting was nice and tight. Everything that came out went back into the car with new components.


New items: lines, compressor, condenser, dryer, expansion valve

With all the install work done, I decided to try to turn on the system BEFORE I drew down the air and added refrigerant. The a/c didn't work in the car when I bought it. The fan never came on. When I turn the switch on the dash, I don't hear the 'hissing' sound other posters have mentioned it should make as the system engages. Nothing but silence and a dead green light on the console.

I've checked the fuses to the right of the dryer (2 fuse boxes mounted to the firewall of the car). Fuses are good. I'm not sure if this is enough to go on. I'm happy to supply images or provide additional details. It's 'fires of hell' hot down here in Tampa and I've got to get this A/C sorted out. Any and all help is much appreciated. Thanks!

OK Dave.....first things first. I have gone through your same problems with My '71 250C and a now departed '73 280C both with Sanden Compressors that I converted from the original Yorks. So......bear with me and we will fix your AC. OK? It is not really that difficult......you just have to understand exactly, and I mean exactly how the entire system works first. Then it will be easy.
1. Did the old system work?

2. Does the New compressor clutch engage?

3. Do you have complete instructions on how to operate the Heating and AC system? ie: Owners Manual or other data?

4. Forget about the Aux Fan for the moment. We'll get to that once we know that the Compressor will engage when the switchology is understood and working.

Give me some feedback on these questions so we know where we need to start. OK?

If necessary I will provide photos and wiring schematics as required.

E'Mail me privately at merc250c@embarqmail.com . Easier and better communication that way.

Charlie

Charlie
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post #18 of 26 (permalink) Old 07-29-2015, 10:07 AM
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From memories of my various 250Cs. The vacuum operated AC on/temperature switch, the AC blower switch, and the pressure switch all have to close to get power to the compressor clutch. It sounds like your vacuum-operated switch isn't working. Maybe it's not getting vacuum, maybe the electrical part is disconnected or has no power to it. Maybe the lever is disconnected, or the flaps are jammed. Until you get that switch to move the flaps you have no hope of AC.

Chuck Taylor
Falls Church VA
1998 SL500
1959 220S
1970 280SL

Last edited by ctaylor738; 07-29-2015 at 10:14 AM.
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post #19 of 26 (permalink) Old 07-30-2015, 08:30 PM
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It is an amazing coincidence that somebody else is working on basically the same project. I have also had many hours of frustration figuring out how to make the system work. I have a 1975 w115 240D with a Sanden compressor that I installed a year ago. My A/C compressor will turn on, but only by bypassing the changeover switch. I run a three wire contraption at the location of the changeover switch to activate the compressor. The A/C runs 100% of the time which is no big deal to me since I live in Florida, but i would love to have the system work properly.

I thought that the changeover switch was faulty, so I finally found a replacement and installed it. Unfortunately, the replacement did not fix the issue and now my A/C compressor will not turn on again. The properly installed changeover will activate the vacuum flaps when I turn to the A/C knob on and off, but does not energize the A/C compressor. I have messed around with the switch while installed in the car and I can't energize the A/C. I am interested in the "switchology" so if anybody has anything else to share I would love to hear it. I added a crappy copy of the A/C wiring that may help out somebody.
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post #20 of 26 (permalink) Old 07-31-2015, 04:10 AM
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It is an amazing coincidence that somebody else is working on basically the same project. I have also had many hours of frustration figuring out how to make the system work. I have a 1975 w115 240D with a Sanden compressor that I installed a year ago. My A/C compressor will turn on, but only by bypassing the changeover switch. I run a three wire contraption at the location of the changeover switch to activate the compressor. The A/C runs 100% of the time which is no big deal to me since I live in Florida, but i would love to have the system work properly.

I thought that the changeover switch was faulty, so I finally found a replacement and installed it. Unfortunately, the replacement did not fix the issue and now my A/C compressor will not turn on again. The properly installed changeover will activate the vacuum flaps when I turn to the A/C knob on and off, but does not energize the A/C compressor. I have messed around with the switch while installed in the car and I can't energize the A/C. I am interested in the "switchology" so if anybody has anything else to share I would love to hear it. I added a crappy copy of the A/C wiring that may help out somebody.
Unfortunately, the component labels on your diagram are nearly illegible on my display and I'm 200 miles away from my FSM this week. so I'm going by memory of how my '72 W114-115 AC worked.
Does your change-over switch activate the heater-fan in the dash, then the AC blower in the console as needed? Do you have power to the AC compressor thermostat? In the OP's photo it's one of the two green wires connected to the square metal device in the console, controlled by the rotary AC knob. When the thermostat is getting power and it's connecting to the compressor, you should have 12V at both wires.

Happy Motoring, Mark
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