Automotive Air Conditioning Information Forum

i have a 2006 mercury grand marquis. ac has been working fine. yesteday while at idle and the compressor kicked on rpm droped 1000 rpm, this has not been the normal opperation. also engine cooling fan not coming on. ac comprssor kicking on and off every 5 seconds or so. installed gauges, with compressor on, no cooling fan, high side 400 and low side 130 or pegs the gauge. hot wired engine cooling fan and it runs, but will not come on by itself. replaced the cooling fan module, no diffence, replaced cylinder head temp sensor, still no engine cooling fan. why are my low and high side pressures so high and stalling the engine at idle?

Sounds like it might be overcharged. Was anything done to the system recently that might have caused the change in operation, for instance, "topping off" the refrigerant with one of those charging kits having an attached gauge?

no nothing has been done. has been operating ok all sumer untill yesterday

There should be a cooling fan Relay as well as the control module.

(insert rant here about engineers adding solid state modules where a relay will do just fine)

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What do the pressures look like when you run battery voltage directly to the fan?

JohnHere wrote: ↑Mon Aug 07, 2023 8:12 pm What do the pressures look like when you run battery voltage directly to the fan?

will try that tomorrow, but as soon as i turn the ac on, pressures go instantly to 130 or more on low side and 400 or more on high side and pulls the engine down. the high side line gets hotter the heck in less than 5 min.

There is a puller fan on the engine side of the radiator. My guess is that your fan is toast and the clutch fan can't draw enough air to remove the heat from the condenser, thus the pressure rises and your cooling is diminished.

2006 & up Grand Marquis has NO fan clutch. Stop guessing if you don't know Tony.