4mA * 220 = 880 mA < 1A. What kind of transistors are you using in the high side, NPN also? NPNs don't work in the high side of a bridge without special considerations (which I won't get into, because you probably are using PNPs). I would guess your problem is probably "shoot through," the high side and low side transistors in the same leg on at the same time. You need some dead time between turning one off and the other on to allow the transistor to turn off. This is particularly important when driving an inductive load. Do you have "snubbers" and or reverse diodes across the transistors as well, otherwise they may be failing from overvoltage. Do you have a scope? If you do, you can monitor the current through the transistors (on the low side, if you don't have isolated channels) by putting a small (1/4 ohmish) resistor in series with the emitter and monitoring the voltage across it. If you have shoot through, you will see very short spikes of extremely high current, which won't last long because the transistor will probably fail.
j.