Compressor/clutch not coming on. Unplugged the pigtails connected to the compressor and turned ignition on with A/C set to max and tested with volt meter. Nothing!!! Zero voltage. I checked the 30 amp fuse and it is good. Ready to attack the controls for vacuum leak, but don't know where to start. Any good "this is how to remove '91 Bronco climate controls" sites? Don't really want to start breaking plastic. Any other possibilities that may cause the symptoms that I need to look at before looking at the vacuum? All of the other controls (heater, defrost, vent ) work fine. Thanks.....

 

Before going a single step further, make sure the system has a decent refrigerant charge. If there is not enough initial pressure in the system BEFORE the compressor is turned on, the power to engage the clutch WILL NOT come through the clutch trigger pigtail. This is a fail-safe that prevents you from trashing a compressor in the event the system leaks or discharges completely. There is a pressure switch in the system that determines this. IF the system does indeed have enough of a refrigerant charge to be operating properly, THEN you can pursue other possible causes.

 

Welp, Greystreak....you nailed it again. Only 18 lbs of pressure. Can they convert this system from R12 to 134A or am I stuck with paying $65 a can (3) every two or three years when it leaks out? Sure do thank you for your input. Saving me a heap of time, trouble, and money.....

 

I'm interested in this also. I've chased down most of the issues with my "new" truck, and I'm now left with the A/C, T-Case shift motor, and wiper issues.

Is there a good write-up on this that 3Nails and I can refer to?

 

You can buy a compressor that has been rebuilt to run R134 but the cost is about the same as buying the R12.

 

I have converted my F150 over to R134a and it cools really well but there is a big cost up front if you want to do it right. There are plenty of guys who do quick-and-dirty conversions and sometimes they work, for a while, but I would not do it to my truck. I replaced the compressor, the manifold hose assy (you need barrier hoses), the liquid line, the orifice tube, the accumulator, and the condensor. About the only thing left from the R12 system is the evaporator core.

Now, you don't have to replace the compressor, I did that because my compressor was bad. If your compressor is good, just drain all the mineral oil out and replace it with ester oil. Mineral oil is not compatible with R134a. You will also need to flush out the evaporator core to remove mineral oil from that.

You can get your existing manifold hose assy. converted to barrier hoses if you can find someone to do it - look for a place that makes hydraulic hoses or who specializes in a/c hoses. If not you can buy one for a 94 model, which is what I did.

Buy a 94 condensor but you will have to mod the brackets a bit to make it fit in the 91 core support. It's not major but you also need a hose made to adapt the 94 condensor to the liquid line - the fittings are different. Again, you need a place that makes hoses for this. If this is too much hassle, you don't have to replace the condensor, but if you don't, your a/c is gonna warm up on you at idle (like at a stoplight) when there's not much air movement. R134a needs about 50% greater condensor capacity than R12. You can compensate by adding an electric fan that comes on with the compressor if this suits you.

Use the green o-rings. Charge is about 36 oz. of R134a.

 

Are any of the leak indicator additives any good and do they detect a slow leak? Sure would like to fix the leak issue before the recharge if that's the way I go.

 

What year did Ford change from R12 to R134a? If I can find a complete unit at the JY, I'll pull the whole thing.

 

That would be 1994. If you use the 1994 evap core then the 94 liquid line will work and you won't need to make one like I did.

 

...then that's my next project.

Thanks!