1997 Chevy Suburban

Hi, there is a compressor relay, voltage to the relay goes hot when you turn on the key. The PCM grounds the coil side of relay in order to energize relay. The pcm won't ground the relay without request. The request comes from the hvac control module. I'd check for any possible trouble codes, to see if a code could point me in the right direction, otherwise, I'd have to backtrack the circuit.