( ( Heat ( from ( outside air ) ) ) ( ( vaporizes ( ( ( the ( liquid refrigerant ) ) , ) ( which ( ( becomes ( a ( low-pressure ( , ( low-temperature ( ( gas and ) returns ) ) ) ) ) ) ( to ( the compressor ) ) ) ) ) ) . ) )
(ROOT (S (NP (NP (NNP Heat)) (PP (IN from) (NP (JJ outside) (NN air)))) (VP (VBZ vaporizes) (NP (NP (DT the) (JJ liquid) (NN refrigerant)) (, ,) (SBAR (WHNP (WDT which)) (S (VP (VBZ becomes) (NP (DT a) (JJ low-pressure) (, ,) (JJ low-temperature) (NN gas) (CC and) (NNS returns)) (PP (TO to) (NP (DT the) (NN compressor)))))))) (. .)))
Heat from outside air vaporizes the liquid refrigerant, which becomes a low-pressure, low-temperature gas and returns to the compressor.
(ROOT (S (NP (NNS Gases) (CC and) (NNS liquids)) (VP (VBP become) (NP (NNS solids)) (PP (IN at) (NP (JJ low) (NNS temperatures)))) (. .)))
Gases and liquids become solids at low temperatures.