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Jim Grant Tech Tips Jim Grant Tech Tips
A collection of helpful articles based on reader submissions
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  Jim Grant's Tech TipsJim Grant's Tech Tips
Below is a collection of Jim Grant's Tech Tips sorted by Vehicle Make. These Tech Tips were answers to questions submitted to Jim by users over the course of many years.
If you have any questions, please feel free to email us.



Lincoln - Mercury
  Jim Grant's Tech Tips

‘89 Ford Aerostar, A/C Problems
Q: I have an ‘89 Ford Aerostar and the air conditioner takes a break when it's hot enough to really need it. When the temperature’s at or below 80, it's ice cold; much above 80 and everything seems to work except the compressor. By turning it 'OFF' and then back 'ON' (sometimes 6 or more times) it will kick in and cool for a short period. It's been "looked at" several times and it seems fine. There are no freon leaks, gas pressure is normal. I have had "wide open throttle " switch replaced twice, it made no difference. Where's the thermostat ? HELP! I'm going to be in Florida this summer! This isn't the model year with the catch-fire wiring, is it ? ....... Jean

A:You want to ask the person who diagnoses your problem to perform a voltage drop test from the battery to the A/C compressor’s electric clutch assembly. Watch their eyes closely when you say this. Why? Either they are going to look bumfumbled because they don’t know what you’re talking about (which means get out of that shop), or there will be a look of understanding mixed with curiosity, wondering how you would know about that test procedure. One of the problems we’ve seen with A/C systems such as yours has been a loss of battery voltage available to the A/C compressor clutch. The condition is not a complete loss, it’s just a drop in voltage available which is just enough to cause problems. This doesn’t present a problem until the temperatures climbs. As the A/C system works harder (high air temperature) the demand for electricity increases. An electrical circuit just by its nature will make its own heat. This internal heat interferes, actually creating more internal resistance, reducing the flow of electricity even more. The end result is an A/C system that will stop working when you really need it. The fix is identifying the switch or contact that is resisting the flow of electricity or installation of a relay kit to provide power to the A/C compressor.

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