Help!!! A/C Electrical Trouble shooting

[rswamy]

New to this site, absolutely love it. I bought this 84 911 Carrera a month ago. Came with a non-working A/C, rebuilt compressor per owner. The owner is a really great guy, still helps me out and answers any questions.....

Me and my skills.
Mechanical engineer, worked as a aircraft maintenance engineer for a while. Not afraid to open S*%t up, I don't get stressed out if I can't put it back together. The worst case scenario is to call AAA and take it to the shop I realize it costs money. I promise you that was not my attitude as an aircraft engineer . Electronically challenged, I think I have sound electrically fundamentals, I don't stick un-insulated tools in the wall socket for example.

Now the problem,

Here is the last thread the previous owner posted. where he ran into electrical problems.

A/C Fan Circuit: Will someone help me rewire.

I'm looking at the wiring diagram on Bentley page 970-45, some questions..

1. What is "J/C 4 POLE LT" and "J/C 4 POLE LV"? Where are these?
2. If I'm right I found the A/C relay in the evap blower compartment.
3. Where is the condenser relay?

Where I'm at now...
Checked for voltage on the A/C relay with ignition on, both temp knob and fan knob turned to high. The relay was noticeably warm
1. Red/White on relay hot.
2. Black on relay Hot.
3. Red not hot.
4. Yellow not hot.
5. Two male connectors on the relay top not connected to any wires, one of them is hot.

Confused that per the diagram and my electrical skills, red should be hot and makes Red/white hot. CORRECT ME IF I'M WRONG.

Interesting while checking Black wire on relay, accidentally touched a small metal piece (I imaging it is the relay contact post fixed to base of relay case) on the relay right by the black connector and both the condenser and evap motor came on. There was kinda grinding noise in the evap motor like the bearing was bad or something, the sound went away after about 10-15 seconds. That makes sense with the circuit overload from the original post.



Any input will be appreciated...

[Mitch Leland]

After reading the previous posted link it appears that all the information you need it there or at least a good starting point. After cleaning up your connections I'm guessing you have some worn out motors. If you have to replace the evaporator motor then you'll have to R&R the evaporator. At that point you're on a slippery slope since you might as well do an upgrade on the evaporator and the evaporator blower motor. Those two items will make a big difference in the performance of your A/C. Sooner or later if you want a good working A/C system you'll do this anyway. Both items are available through our host.

It's not a bad project and you'll do yourself a lot of good knowing that you've taken care of a big problem instead of half measures. Plus you never know what kind of rust lurks under the evaporator, gone unchecked can it do a lot of damage.

[86 911 Targa]

Originally Posted by rswamy

New to this site, absolutely love it. I bought this 84 911 Carrera a month ago. Came with a non-working A/C, rebuilt compressor per owner. The owner is a really great guy, still helps me out and answers any questions.....

Me and my skills.
Mechanical engineer, worked as a aircraft maintenance engineer for a while. Not afraid to open S*%t up, I don't get stressed out if I can't put it back together. The worst case scenario is to call AAA and take it to the shop I realize it costs money. I promise you that was not my attitude as an aircraft engineer . Electronically challenged, I think I have sound electrically fundamentals, I don't stick un-insulated tools in the wall socket for example.

Now the problem,

Here is the last thread the previous owner posted. where he ran into electrical problems.

A/C Fan Circuit: Will someone help me rewire.

I'm looking at the wiring diagram on Bentley page 970-45, some questions..

1. What is "J/C 4 POLE LT" and "J/C 4 POLE LV"? Where are these?
2. If I'm right I found the A/C relay in the evap blower compartment.
3. Where is the condenser relay?

Where I'm at now...
Checked for voltage on the A/C relay with ignition on, both temp knob and fan knob turned to high. The relay was noticeably warm
1. Red/White on relay hot.
2. Black on relay Hot.
3. Red not hot.
4. Yellow not hot.
5. Two male connectors on the relay top not connected to any wires, one of them is hot.

Confused that per the diagram and my electrical skills, red should be hot and makes Red/white hot. CORRECT ME IF I'M WRONG.

Interesting while checking Black wire on relay, accidentally touched a small metal piece (I imaging it is the relay contact post fixed to base of relay case) on the relay right by the black connector and both the condenser and evap motor came on. There was kinda grinding noise in the evap motor like the bearing was bad or something, the sound went away after about 10-15 seconds. That makes sense with the circuit overload from the original post.



Any input will be appreciated...

The condenser relay is relay #6 on the fuse panel. (closest to the front of the car).

The A/C fuse is fuse #2 as marked on the fuse/relay panel cover.

The A/C relays carry high current loads, and are subject to failure due to contact arcing.

Replace both relays, and verify voltages and grounds as per your Bentley.

Good luck,

Gerry

[rswamy]

Thanks guys, I will replace the relay and get it working first. Then look into upgrades for evaporater. Any other upgrades recommended ? I read some about hoses and 134 conversion? Any recomenndations?

[flskala]

upgrades you ask...... Your stock system (even with a rebuilt compressor) will do very little to cool you off. Read the 1 million threads on it. IMHO, you will need to replace nearly every part of that AC system (ok, except for the compressor) - new barrier hoses, additional condensers with cooling fans, evaporator motor and vents to get more air in the cabin. The cost without labor will be roughly +/- $3K. I am going to have to bite the bullet on the same project by next summer. For now, I'll drive my 993 when it gets real hot...;-). Good Luck!

[brads911sc]

+1

Rennaire and Griffith both have good kits. Our host sells the Renniare that is where I started.

ZIMS makes a good rear wheel condenser that is better than Griffiths IMHO because it doesnt sit right over the exhaust.

Rennaire makes a Procooler in place of the dryer hat some swear by. Comes in their kit. Be sure to get their upgraded dessert duty condenser.

Griffiths makes a killer fan for the Evap.

If you do it all you will have a cool and comfortable cabin on most days.

I went with the Rennaire Kit (compressor, hoses, procooler, front dessert duty conderser, expansion valve, etc). I Added the Kuehl Vents, Keuhl fan, Zims Condenser, and new rear Behr Factory Deck condenser...

Was about 3 k. I did all the work myself.

Originally Posted by flskala

upgrades you ask...... Your stock system (even with a rebuilt compressor) will do very little to cool you off. Read the 1 million threads on it. IMHO, you will need to replace nearly every part of that AC system (ok, except for the compressor) - new barrier hoses, additional condensers with cooling fans, evaporator motor and vents to get more air in the cabin. The cost without labor will be roughly +/- $3K. I am going to have to bite the bullet on the same project by next summer. For now, I'll drive my 993 when it gets real hot...;-). Good Luck!

[rswamy]

Update:

Replaced the A/C relay, got one cheap ($8) at O'Reilly's everything works fine. Now I need to evacuate and recharge. Any Idea what I'm looking at for R12 recharge. If it is going to be a few hundred bucks, I may explore the complete system upgrade.

[rswamy]

Do you recommend new dryer before a recharge? Looks like I have to start working on a budget for the new A/C system.

[86 911 Targa]

Originally Posted by rswamy

Do you recommend new dryer before a recharge? Looks like I have to start working on a budget for the new A/C system.

Here is what we did on our '86.

1. Replaced the stock evaporator with the Rennaire high flow unit.

2. Replaced the stock dryer with the Rennaire two stage dryer.

3. Re-adjusted the console mounted A/C temperature switch for a 38 degree compressor shut-off at the center duct, and more importantly, a 10 degree on/off cycle window 40-50 degrees thereby elimenating evaporator freeze-up which had been a constant issue in our humid environment.

Please see my previous A/C post(s) of May 9 for performance results.

I think that you will be surprised at the cost v/s results.

You may pm me.

Good luck,

Gerry

[Hugh R]

Last time I looked the going rate was in the range of $100/pound for R-12. I'm not sure what a stock system holds, but 2 to 2-1/2 pounds is my guess.

[86 911 Targa]

Originally Posted by Hugh R

Last time I looked the going rate was in the range of $100/pound for R-12. I'm not sure what a stock system holds, but 2 to 2-1/2 pounds is my guess.

Hugh,

On our '86 it is 3 pounds.

Gerry

[Barrpete]

Originally Posted by rswamy

Do you recommend new dryer before a recharge? Looks like I have to start working on a budget for the new A/C system.

If the system has been opened up for a while, then it will have absorbed a bunch of moisture and should be replaced. A new dryer is not that expensive.