diff --git a/auto_cpufreq/core.py b/auto_cpufreq/core.py
index bb44ae2..66cdc34 100644
--- a/auto_cpufreq/core.py
+++ b/auto_cpufreq/core.py
@@ -457,42 +457,66 @@ def display_load():
 
 # set minimum and maximum CPU frequencies
 def set_frequencies():
-    conf = get_config()
-    section = "charger" if charging() else "battery"
+    """
+    Sets frequencies:
+     - if option is used in auto-cpufreq.conf: use configured value
+     - if option is disabled/no conf file used: set default frequencies
+    Frequency setting is performed only once on power supply change
+    """
+    power_supply = "charger" if charging() else "battery"
+
+    # don't do anything if the power supply hasn't changed
+    if (
+        hasattr(set_frequencies, "prev_power_supply")
+        and power_supply == set_frequencies.prev_power_supply
+    ):
+        return
+    else:
+        set_frequencies.prev_power_supply = power_supply
+
     frequency = {
         "scaling_max_freq": {
             "cmdargs": "--frequency-max",
             "minmax": "maximum",
-            "value": None,
         },
         "scaling_min_freq": {
             "cmdargs": "--frequency-min",
             "minmax": "minimum",
-            "value": None,
         },
     }
-    max_limit = None
-    min_limit = None
+    if not hasattr(set_frequencies, "max_limit"):
+        set_frequencies.max_limit = int(getoutput(f"cpufreqctl.auto-cpufreq --frequency-max-limit"))
+    if not hasattr(set_frequencies, "min_limit"):
+        set_frequencies.min_limit = int(getoutput(f"cpufreqctl.auto-cpufreq --frequency-min-limit"))
 
-    for freq_type in ["scaling_max_freq", "scaling_min_freq"]:
-        if not conf.has_option(section, freq_type):
-            frequency.pop(freq_type)
+    conf = get_config()
 
     for freq_type in frequency.keys():
+        value = None
+        if not conf.has_option(power_supply, freq_type):
+            # fetch and use default frequencies
+            if freq_type == "scaling_max_freq":
+                curr_freq = int(getoutput(f"cpufreqctl.auto-cpufreq --frequency-max"))
+                value = set_frequencies.max_limit
+            else:
+                curr_freq = int(getoutput(f"cpufreqctl.auto-cpufreq --frequency-min"))
+                value = set_frequencies.min_limit
+            if curr_freq == value:
+                continue
+
         try:
-            frequency[freq_type]["value"] = int(conf[section][freq_type].strip())
+            frequency[freq_type]["value"] = (
+                value if value else int(conf[power_supply][freq_type].strip())
+            )
         except ValueError:
             print(f"Invalid value for '{freq_type}': {frequency[freq_type]['value']}")
             exit(1)
 
-        if not max_limit:
-            max_limit = int(getoutput(f"cpufreqctl.auto-cpufreq --frequency-max-limit"))
-        if not min_limit:
-            min_limit = int(getoutput(f"cpufreqctl.auto-cpufreq --frequency-min-limit"))
-
-        if not (min_limit <= frequency[freq_type]["value"] <= max_limit):
+        if not (
+            set_frequencies.min_limit <= frequency[freq_type]["value"] <= set_frequencies.max_limit
+        ):
             print(
-                f"Given value for '{freq_type}' is not within the allowed frequencies {min_limit}-{max_limit} kHz"
+                f"Given value for '{freq_type}' is not within the allowed frequencies {set_frequencies.min_limit}-{set_frequencies.max_limit} kHz"
             )
             exit(1)