#1  
Old 04-22-2020, 04:49 PM
jays55's Avatar
jays55 jays55 is offline
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Talking 1977 Lemans Can Am .... Dash Ventilation Controls Prevent Engine Firing ???

I have a 1977 Can Am (Lemans Sport with a Grand Prix dashboard). I was driving the other day and decided to test the different functions of the A/C system (MAX, NORM, Vent, Htr, etc). Everything seemed to function correctly.

After a quick stop, the engine would not fire. The starter turned over, but the engine would not start. Additionally, all of the factory dash gauges were going crazy while the ignition was in the "start" position. I began to look for anything I may have changed, to undo it. I had left the A/C control lever in the Vent position. I moved the lever back to Off. Bam, the engine fired right up!

While driving home, I moved the A/C control lever through all positions and everything again seemed fine. I did notice the oil pressure gauge was twitching a bit either side of normal. The other gauges looked fine.

I moved the lever back to Off, before shutting down the engine and it started right back up again. I would like to correct this, if anyone has a suggestion. Electrical is not my strong suit, so anyone with knowledge could probably save me a lot of time

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  #2  
Old 05-04-2020, 10:58 PM
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73LeMans 73LeMans is offline
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Nice car man. I'm no electrical wizard, plus most of my cars original wiring is no longer used and all of the HVAC stuff has been removed. Im surprised no one has chimed in, but it sounds like you need to look under the dash to see whats happening when you move to the vent. (if you can even witness anything) Sounds like something is grounding. If no one responds here, try the Pontiac - Street Section of the board, or the 73-77 A-body TECH section, for help more specific to these cars.

You the original owner? Maybe it was someones cool theft deterrent.

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  #3  
Old 05-05-2020, 10:51 AM
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Ben M. Ben M. is offline
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Amusingly enough I went through this with a slightly older car ('73). It turns out there is a temperature switch that operates the compressor in the head unit - it prevents the compressor from running if the temperature is below freezing. Mine had failed internally with a partial ground short. It dragged my entire +12V in the dash down and intermittently caused a ground problem. Kept the car from running and eventually would just blow the fuse for the AC blower, then the car would run again. You need to check the wiring in the head unit or dash for something similar.

  #4  
Old 05-06-2020, 12:52 PM
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jays55 jays55 is offline
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Thanks for the input. I have been driving the car more and just moving the Climate Control lever to Off before shutting down the engine and while starting. Lazy man's fix, but it's working! Right now the R134 A/C system is not charged. I will be getting it charged when summer temps arrive and see if that makes any difference.

When the car was restored, a factory 1973 Harrison evaporator box was installed in the firewall, along with a VIR Elimination Kit (external electric control switch on the accumulator). I recently converted it to R134a using an Original Air conversion kit, but haven't had it charged, yet.

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