90 ford 150 a/c works for a few minutes


Old 07-07-02, 05:09 PM
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Join Date: Feb 2001
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90 ford 150 a/c works for a few minutes

Looking for some help.
Just checked the a/c system on my B.in laws 1990 Ford F150 6 cyl truck.
Hooked up gauges and read 30 lb.on the low and 225 lb. on the high side and clutch engaged on & off every 30 sec. so I added 12 oz. and it kept running.
Let the truck idle for 20 minutes or so and all was fine then took it out for a drive.
Low speeds around 25-30 for 2 miles then stopped for 5 min. at the store at idle and still cooling.
Drove out the highway and in 2 miles you could tell the comp. quit since it was starting to get warm.
Opened hood on side of road and it had quit.
Switched off at control heading down the road and drove 2 more miles and switched unit back on and it started to cool again.
tried this 2 times and the second time after it quit we quickly pulled to his drive and flushed out the condensor for 5 minutes but it never engaged , actually not real dirty plus pressure change didnt help doing this.
Shut truck off and waited 10 min and tried again and all fine for awhile untill you run up on the speed.
The main first problem he complained to me about was that running down the highway it worked fine until slow speed and it would cut down, signs of being low.
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Old 07-07-02, 07:14 PM
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Monitor your gauges while raising the rpm's on the truck.Your high side should gradually rise while the low side should fall.Your original pressure readings weren't that far off. Also you might check and make sure this thing's drain is ok,you should see water dripping out under the truck,it could be freezing up without proper
If all ok on items mentioned,when compressor shuts off again,unplug the pressure switch and use a piece of wire and jump across the harness which will make the compressor run continually.if when doing this the pressures stay around 230-240 high side and 30-40 low side ,you might try a new pressure switch.
Old 07-08-02, 03:43 AM
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I agree with Fordtech. Might also suggest a new orifice screen too.
Old 07-08-02, 02:39 PM
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When the unit disengaged(clutch) I did jump across pressure switch and it did not engage clutch.
However I did not think about checking for condensation drainage.
I guess sometimes a person forgets to overlook the easiest things first.
Ill find up on this and get back.
Thanks for the info
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