responded properly by comparing the measured value with the stored value 34 x 34 if the measured value exceeds the stored value there is a problem with modulation valve 64 and step 530 initiates shut down of unit 20 by setting flag sdf true and program 286 exits at 532 when step 528 finds that the current draw measurement of step 526 does not exceed the stored value 34 x 34 modulation valve 64 responded properly to step 524 and step 528 proceeds to steps 508 and 510 which executes the requested mode change lsc hg with modulation if the request is still valid when step 520 finds that the current draw measurement of step 518 passes the upper limit test of step 520 step 584 determines if modulation valve 64 is energized by comparing the current draw measurement of step 518 with the stored value 34 x 34 if the current draw measurement does not exceed the stored value 34 x 34 modulation valve 64 failed to close at all step 586 de energizes driver line 228 to valve 64 step 588 records alarm code modc which indicates the modulation valve 64 and its circuitry should be checked and the alarm icon is flashed unit 20 is allowed to run without suction line modulation by proceeding to step 608 which resets the stored value 34 x 34 to zero and step 608 proceeds to steps 508 and 510 which implement the lsc hg mode without modulation and program 286 exits at 512 when step 584 finds that the current draw measurement of step 518 passes the lower limit test step.