Whitaker717 Posted July 19, 2022 Share Posted July 19, 2022 Hey guys, back at it again working on this truck. Lol. I have an 87 4.0 that came with factory air. Currently not working, looking to get it going. After looking at a few threads I got a few ideas. Compressor doesn’t kick on or anything. Fan blows nice and fast. I took the low pressure switch out and jumped it with a paper clip. Low and behold the electric fan turned on. I didn’t really hear the compressor come on though. Can someone tell me if I am on the right track? I’m hoping compressor isn’t shot but I really don’t know. Any guidance would be appreciated. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 19, 2022 Share Posted July 19, 2022 Well the compressor is controlled by a relay in the Renix relay center(I don’t know which one it is in the factory set up, cruiser has a pic of it). If you jump that it should engage the clutch and probably get it to spin. That being said if you do this and the system is out of refrigerant, do NOT run it for long. Hell 3 seconds to see the compressor move and hear it should be enough. Link to comment Share on other sites More sharing options...
Whitaker717 Posted July 19, 2022 Author Share Posted July 19, 2022 So when I jumped it, the e fan came on and I could see the inside of the compressor moving. I’m hoping that’s a good thing. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 19, 2022 Share Posted July 19, 2022 What do you mean by inside of the compressor? Are you referring to the clutch on the pulley? Link to comment Share on other sites More sharing options...
Whitaker717 Posted July 19, 2022 Author Share Posted July 19, 2022 I took the nut off the top and I could see it turning through the oil fill hole. Only let it run for about 2 seconds Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 19, 2022 Share Posted July 19, 2022 Ohhhhhhhh. Sounds like to me the system may not have any refrigerant in it if it doesn’t kick on. That being said if you jump the low pressure switch and it doesn’t engage the clutch and move the pulley then the relay could be bad. Now are you absolutely certain this system is still charged? Link to comment Share on other sites More sharing options...
Whitaker717 Posted July 19, 2022 Author Share Posted July 19, 2022 Not at all. Lol. I doubt there is any coolant at all in it. Is it hard to recharge? Can I just buy the stuff in the can and give it a try? Now let me ask you this, if I did get some refrigerant in it, would the low pressure switch then allow it to kick on? Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 19, 2022 Share Posted July 19, 2022 It’s not hard to recharge if you have an idea but the system requires 2.4lbs of R12(I think as the conversion asks for less R134)or 2.32lbs of R134. But the system has to be completely void of anything else. So if there is a leak, there’s probably moisture in it. If it’s just low then maybe a can in it will trigger the low pressure switch to engage and get the system running. All the low pressure switch does is prevent the system from running if there’s nothing in it. Link to comment Share on other sites More sharing options...
Whitaker717 Posted July 19, 2022 Author Share Posted July 19, 2022 In theory doe this mean the compressor still works though since it came in when jumped? Link to comment Share on other sites More sharing options...
cruiser54 Posted July 19, 2022 Share Posted July 19, 2022 Yes, sorta. Go have it diagnosed at a shop. Link to comment Share on other sites More sharing options...
Whitaker717 Posted July 19, 2022 Author Share Posted July 19, 2022 21 minutes ago, cruiser54 said: Yes, sorta. Go have it diagnosed at a shop. I plan on it for sure. So you think I can add a can of refrigerant and see what happens or will it do more harm than good? Link to comment Share on other sites More sharing options...
cruiser54 Posted July 19, 2022 Share Posted July 19, 2022 This is likely to be expensive. Probably just a waste of time and money to throw a can of expensive refrigerant in. Let the shop do it. The system will need to be evacuated, and certain components replaced, along with a conversion to R134a refrigerant. How much money are you thinking of throwing at this? Budget? Link to comment Share on other sites More sharing options...
Whitaker717 Posted July 19, 2022 Author Share Posted July 19, 2022 Till it’s fixed. I have spent about 15-18k on this pos truck so far. Lol. I’m not stopping now. Link to comment Share on other sites More sharing options...
cruiser54 Posted July 19, 2022 Share Posted July 19, 2022 cool. Take it to a shop then and save yourself a ton of frustration. Link to comment Share on other sites More sharing options...
Whitaker717 Posted July 19, 2022 Author Share Posted July 19, 2022 Will do. Thanks Cruiser. Link to comment Share on other sites More sharing options...
Andy in Pa Posted July 19, 2022 Share Posted July 19, 2022 Where is the low pressure switch located? I am working on an AC system as well, and have not found the low pressure switch yet.. I jumped 12vdc to the AC clutch though with it not running and the clutch is working. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 19, 2022 Share Posted July 19, 2022 Low pressure switch should be attached to the dryer. Regardless of the engine Link to comment Share on other sites More sharing options...
Andy in Pa Posted July 19, 2022 Share Posted July 19, 2022 3 hours ago, eaglescout526 said: Low pressure switch should be attached to the dryer. Regardless of the engine Aha, ok thank you. I have a new dryer to put on, but have not pulled the old one out yet. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 19, 2022 Share Posted July 19, 2022 Welcome. Link to comment Share on other sites More sharing options...
Andy in Pa Posted July 20, 2022 Share Posted July 20, 2022 The new dryer has a new pressure switch attached as well. Link to comment Share on other sites More sharing options...
eaglescout526 Posted July 20, 2022 Share Posted July 20, 2022 1 hour ago, Andy in Pa said: The new dryer has a new pressure switch attached as well. That must be nice. The two dryers I have didn’t come with one and the original one from the MJ my parts were pulled from had a broken prong. Link to comment Share on other sites More sharing options...
Andy in Pa Posted July 20, 2022 Share Posted July 20, 2022 17 minutes ago, eaglescout526 said: That must be nice. The two dryers I have didn’t come with one and the original one from the MJ my parts were pulled from had a broken prong. I grabbed a new one on Rockauto. I think it was $15 or so. The pressure switch was capped off like a fitting, so I didn't realize what it was until I looked at the old one. Link to comment Share on other sites More sharing options...
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