HVAC air flow switching to defrost under heavy engine load on Plymouth Acclaim

Problem Description and Possible Solution

The heating, ventilation and AC (HVAC) system may  change to defrost mode under heavy engine load conditions when low engine vacuum is produced. This can often be corrected by installing an additional vacuum check valve with reservoir to help stabilize the vacuum supply to the HVAC system.

Problem Data
RepairPal Verified
Average mileage: 62,500 (30,000–95,000)
6 model years affected: 1990, 1991, 1992, 1993, more1994, 1995
9 people reported this problem
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Problem as described, but not repaired.