A 5 ton heat pump system with R22 was improved by Liquid Pressure Amplification (LPA) and refrigerant injection technologies. Three approaches for refrigerant injection were used. The first one was by mixture injection in suction line through accumulator; the second one was by liquid refrigerant injection through discharge line, while the third was a hybrid injection, in which vapour and liquid refrigerant were injected both simultaneously. For both approaches two and three LPA technique was used. The range of volume ratio of injected mixture and liquid was 1 to 7%, and 1 to 10% respectively, and in the hybrid injection, the volume ratio of injected mixture was 1 to 3% and for injected liquid was as mentioned above. The following improvement in cycle performance factors were achieved, for mixture injection 5.33%, for liquid injection 29.4%, and 33.45% for hybrid injection. The effect of condensing pressure on the cycle performance was studied also in this work.