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Jun 15, 2011 | 01:11 PM

#16

CR3999

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From: Katy TX

I didn't have to do that because I didn't lose any refrigerant. There was a valve there to stop it. now what do ya think the pressure should be? It is 100 degrees today. Does 45 seem like a good fiqure?

Jun 15, 2011 | 09:15 PM

#17

projectSHO89

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From: St Louis

For an R134a system, static pressure in PSI is about 1.0 to 1.2 times the ambient temperature in degrees F.

Jun 16, 2011 | 10:10 PM

#18

greg_23805

Mountain Pass

Joined: Sep 2002

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Go to this website for a pressure/temperature chart for 134a:
Pressure - Temperature Chart for HFC-134a

With a low side pressure of 45 pounds, the saturation temperature of 134a is 49.61 degrees, let's say 50 degrees. The low side pressure switch will not cutoff the compressor until the pressure gets down to 22-24psi.

Here's what you can try. Set the a/c at max ac and high fan. Connect gauges to the low and high side. Have someone hold the throttle at 1500 rpm and watch. When and if the compressor cuts out, what are the low and high pressures?

If the compressor does not shut off, increase the rpm of the engine more. As you increase the rpm, the low side pressure will continue to drop to a point. If you can get the compressor to cutout by increasing the rpm, either it cutout at 22-24psi on the low side or it cutout because the high side got too high.

Is the condensor coil clean of bugs, rocks and dirt?

Let us know what happens.

Jun 20, 2011 | 11:20 AM

#19

CR3999

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From: Katy TX

OK, I put the gages on the truck yesterday and at idle it would read 40psi and at 1200rpm's it read 30psi. I did it early in the morning so the temp was only 82 degrees out side. I forgot what the high side was but I have the notes in the truck. I didn't do any adding or anything to the system, I wanted to see what you guys thought. It sounds to me that it may be a little low on refrigerant per an earlier post. The truck has 222,000miles on it. What is this shim thing you speak of and how hard is that to check or fix. Man it sure is hot down here hehehe.

Jun 20, 2011 | 09:32 PM

#20

greg_23805

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Run the truck up to 1500 to 2000 rpm when it's above 90 degrees and tell us what the pressures are on the low and high side. Does it cutout when the low pressure goes down to around 24 or less psi? If so, it is low on freon. Knowing how low it is is the challenge. You could charge it with the engine running at whatever rpm it cutout at before, with the system in normal a/c, not Max a/c! Charge until the compressor does not cutout. Leave the can upright so you are only putting gas in the system and not liquid.

If you had a digital temp probe for reading the pipe temps, you could charge it more accurately.

Jun 29, 2011 | 09:03 PM

#21

SabreF150

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Quote:

Originally Posted by greg_23805

Thankyou I have posted on this in another forum and been beating my head I like to work on vehicles but auto A/C new to me and only have cheap Walfart guage and a HF thermometer. I am trying this tommorrow I have narrowed it down to depending on ambient temp morning 80 I have short cycling, afternoon 100 dont have it. I thought the the low cycle switch or little low on juice in system.

I do have some questions should I start a new thread I do not want to Hijack anybodys thread Thanks

Jun 30, 2011 | 08:45 PM

#22

greg_23805

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Joined: Sep 2002

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CR, what's the status of your a/c?

Heh, just noticed you are in Katy, TX. I lived in Cat Spring from 1990 to 2005. Live in North Carolina now.

Let us know what's up.

Sabre, maybe best to start new thread if you haven't already.