The F° or C° readout flashes and I have no compressor engagement. I know on a same vintage GM truck it would be a bad control head. I assume it's the same deal here. Any thoughts ?

 

The compressor is locked out most likely due to low refrigerant or just from winter. There is a procedure to reset but I forget what it involves right now...its some sequence of button pressing on the HVAC panel on the dash. The flashing F is telling you its locked out.

 

Low freon!

 

If it's low on r12 here is a legitamate r12 substitute I used in the system of my 86 f250. It works great. Don't even bother considering a conversion to r134a unless you go to a completely new system, it doesn't cool as well in an r12 system.

 

 

Disconnecting the battery will clear the lockout if the condition was temporary or after repairs are made

 

I saw how to do the diag with the control head online. Mine wont do it at all. I did bypass the pressure cycling switch which led me to the control head. It was low on refrigerant so I added a can of R12A(which I've found works great) and still nothing. I'll disconnect the battery tonight and try again.

 

I may have done the push button diag wrong. Anybody have the correct procedure ? and do '91s have it ?

 

If the F is flashing the compressor won't run, and you won't be able to add refrigerant. On a 92 the ext temp button must be pressed at the same time as the off button. Hold for 5 seconds. This will put the system in diagnosis mode. A code should come up, 09 is low freon. If 09 is displayed press he off button and the code should clear, F no longer flashing and compressor enabled for charging. This is from the 92 shop manual, don't know if 1991 is the same.

 

Thanks, i'll try it tonight.

 

Thanks Oldsmaniac ! It worked. was code 09. I added two cans of r12a and she blows ice cold now. I need to dig out my leak detector ,and find where it all went. Thank you all.

 

Cool!! My 1st wagon had the electronic system while my now wagon is non electronic. I converted it to 134a and it worked for a couple of seasons, but now has a pretty big leak, have not researched the trouble yet....

 

I used r12a not r12. its already been converted to r134 but was almost empty. I worked for GM as a tech for many years. I've seen and done r134 conversions and never really been happy with results. I'm not a fan of r134. This r12a is all over ebay for cheap.I'm told it's not legal in this country because its flammable. But I guess that's gonna change. It works great. Fatter molocule so it even leaks out slower. No need to evacuate, change seals or oil. Mixes with any oil or refrigerant. Use a third as much and runs at lower pressures.

 

Oops, spoke too soon. Still blows cold but F is flashing intermittently and now has code 08. Anybody have a list of the codes ?