I am currently working on a a/c system in my 87 fiero with a 3800 sc swap. I shorted out the LT blue wire (22) going to the pcm. The engine quit and fried the fuel pump relay when this happened. Now I keep getting a P1651 code and the A/C pump will not go on. I checked all the relays and reset the code but it keeps coming back.

My question is did I fry my PCM?

P1651 is indicating your PCM isn't seeing the cooling fan relay. Did you hook it up?

Lt Blue that goes to pin 22 is AC Request Input. Shorting it to ground should have blown your A/C fuse but since it is an input to the PCM should not have affected it.

Did you hook up your A/C pressure transducer? It's needed for the PCM to run the A/C.

Just wondering, but how is your fuel pump relay fried? Did it smoke or something?

[This message has been edited by phonedawgz (edited 05-29-2013).]

quote Originally posted by phonedawgz: P1651 is indicating your PCM isn't seeing the cooling fan relay. Did you hook it up?

yes the relay is connected and the fan works. I even tried a new relay. also why is my compressor not coming on?

Is your PCM showing +12 on the light blue wire?

What voltage is showing on your A/C pressure transducer sensor?

If you ground the Dk Blue wire to the relay, does the relay activate and does the compressor turn on?

quote Originally posted by phonedawgz: Is your PCM showing +12 on the light blue wire? What voltage is showing on your A/C pressure transducer sensor? If you ground the Dk Blue wire to the relay, does the relay activate and does the compressor turn on?

I did check the LT blue wire with a test light and it lit up fine, I will check to see what power that is coming from it when I have a chance.

Can you tell me what the A/C pressure transducer sensor is? Is it the pressure switch on the accumulater? If so there is power coming from it, I would have to check the voltage tho.

The compresser does activate, I bypassed the relay and it works fine. I will try grounding the the dk blue like you said.

The 3800 PCM, and many (most) modern GM PCMs use a 3 pin pressure transducer on the high pressure line. This allows the PCM to determine the pressure on the high pressure side and to decide if it should turn on the relay.

The pressure transducer needs 3 wires to it.

A - Black - Blue pin 80 - Sensor Ground
B - Gray - Clear pin 34 - +5v
C - Red/Black - Clear pin 27 - Sensor output

With any luck you already have the sensor on the aluminum line right behind the A/C compressor. GM located the sensor there on full sized cars. On mid sized cars the sensor is located on the same HIGH line, but is at the firewall or fenderwall usually.

quote Originally posted by phonedawgz: The 3800 PCM, and many (most) modern GM PCMs use a 3 pin pressure transducer on the high pressure line. This allows the PCM to determine the pressure on the high pressure side and to decide if it should turn on the relay. The pressure transducer needs 3 wires to it. A - Black - Blue pin 80 - Sensor Ground B - Gray - Clear pin 34 - +5v C - Red/Black - Clear pin 27 - Sensor output With any luck you already have the sensor on the aluminum line right behind the A/C compressor. GM located the sensor there on full sized cars. On mid sized cars the sensor is located on the same HIGH line, but is at the firewall or fenderwall usually.

Ok I do not have this sensor, I forgot to mention that I am running the fiero A/c compresser with custom lines going to the hard lines.

Do I have to have this sensor to allow the pcm to control the compresser?

Thanks

Yes if the 3800 PCM is to control the compressor.

You really want the PCM to control the compressor. The PCM then compensates when it turns the compressor on and off. The PCM shuts off the compressor if the pressure is too high (and low I believe) It also shuts off the compressor if you floor it and at other times.

The ECM controlled the compressor on the Fiero 2.5/2.8 but then also used pressure limit switches. The 3800 PCM does it a bit more elegantly.

Walking through a junk yard you can find these all the time on midsized cars that have had their engines pulled already. On the full sized 3800s the sensor is located down on the lines right behind the compressor and it's a pain to get it out and it will be all nasty dirty.

If you don't want to make a trip to the yard, email me and I'll ship one that has been cut off for $20.00. Paypal my email if you are wanting one. The fitting needs to be braised/soldered onto your existing high pressure line somewhere (which means you have to evacuate and then later refill your A/C).

[This message has been edited by phonedawgz (edited 05-30-2013).]

to add this would require me to splice into the lines? Is there a easy way to tie it in? or could I tie into the high side pressure port and then run the wires from the front back?

Also how do others do there ac with the stock system and 3800sc pcm?

Usually the bung is soldered/braised to the aluminum line. Since the system needs to be evacuated to do this anyways you can unbolt the line from the body, and unbolt it from the compressor both. Then locate the bung onto either the aluminum line where it bolts to the compressor or where it bolts to the body. Locate it where ever it is easiest for your wiring. Then replace the line, vacuum the system and refill it.

yeah pita

Maybe someone has a work around.

The bung/sensor on an aluminum line -

Thanks for your help so far!

I just filled the system with the redtek. could I install this switch into the back of the compressor? to avoid removing the lines?

Also any ideas on that code issue P1651?