AC Compressor doesn't engage

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roostabunny

roostabunny

10 Year
Joined
Oct 22, 2013
Threads
16
Messages
258
Hey all, I've read around on AC-related threads, but couldn't find quite what I'm looking for.

Here's the basic. 1991 FJ80 (3FE) DD named Vera with non functioning AC. I knew about the AC when I bought it, but it was November in Alabama, no biggie, I'll get to it. Now it's May in Alabama, I've been busier than I expected (not to mention the steering knuckle rebuild) and I care more about the AC every day.

First basic troubleshooting revealed that the AC light came on, but the compressor was not engaging. There's also nothing visible in the sight glass, so simplest explanation was low on refrigerant.

I thought to just throw in a can (Vera's already been converted for R134a) to see if that was the issue (the truck has sat, possibly for years), and then monitor for leaks.

But, (silly me) you can't add refrigerant unless the compressor's running, and by design the compressor won't engage without adequate refrigerant (and the lubricant that goes with it) to protect the compressor internals.

So my questions are...
  1. How do I override that "run dry" protection for long enough to get some refrigerant in? (And is it in the FSM, cause I can't seem to find it!)
  2. Is that the wrong question? Is there something else I should be checking first?
Thanks for any thoughts!
 
Alternatively, just hook a can up to it and hold it upside down. The cans have some pressure in them and may be enough to get the compressor running to suck more into the system. Worked on my 91...
 
1972FJ55 said:
To engage the compressor, there is a pressure switch by the battery. Disconnect it and jump terminals 1 & 2 in the plug and the compressor should engage.
Click to expand...

I looked over by the battery and only saw these, which don't look quite right as pressure switches to me...

0516141244.jpg


This one below, however, looks promising? What do you think? It's over by the sight glass reservoir.

0516141246.jpg

0516141247.jpg
 
R0b0con said:
Alternatively, just hook a can up to it and hold it upside down. The cans have some pressure in them and may be enough to get the compressor running to suck more into the system. Worked on my 91...
Click to expand...

Yeah, I was hoping to be lucky in that way, but nothing happened when I did that.

EDIT: Nothing happened except the pressure in the fill hose went way up. ;)
 
If it's out of refrigerant you need the low pressure switch. If out, the can pressure will be adequate to introduce refrigerant to system thereby closing low pressure switch which should engage compressor so you may complete charging procedure. You can add refrigerant without compressor running


...via IH8MUD app
 
Are you using a manifold to introduce the can of refrigerant or a can with a hose?
 
Reelitchy said:
Don't have any experience running a compressor without freon ( jumping the psi sw) but I would guess it wouldn't take to long to seize it up IMO
Click to expand...

I'm nervous about it, that's why I haven't done it yet. Call me chicken, but I want to do it when I have a helper on hand to jump the switch while I stand ready with the freon.
 
Don't try to add freon the first time you jump the compressor. Just jump it for a couple seconds to make sure it really will engage. If it won't, you have other issues to track down first.

Like others have said, it the systems fine except for being out of freon, you should be able to just dump a can in with the engine off, and then the compressor will engage with the engine and A/C on.
 
CJF said:
Don't try to add freon the first time you jump the compressor. Just jump it for a couple seconds to make sure it really will engage. If it won't, you have other issues to track down first.

Like others have said, it the systems fine except for being out of freon, you should be able to just dump a can in with the engine off, and then the compressor will engage with the engine and A/C on.
Click to expand...

Yeah, quick jump was what I had in mind.

Dump in a can with the engine off? I didn't think that could happen, maybe I'm just thinking that from reading the can.
 
Here's another idea. If the system is empty, use a vacuum pump to put the system into a vacuum and assuming there aren't any large leaks, it will pull the refrigerant in when you hook up the can.
 
Just shoot some in the system. The can is pressurized right? There's no need to jump the pressure sensor. Once the sensor detects sufficient pressure the clutch will engage as long as everything else works. Then find your leak.
 
X2. If it already has pressure it will tell you the problem is elsewhere most likely high or low pressure switch.


...via IH8MUD app
 
CJF said:
Good gawd; jump the d*mn thing already.
Click to expand...

Yeah, yeah - the rest of life gets in the way. ;)

So, as of yesterday - The compressor engages when I short the switch.

I couldn't tell if I was getting flow from the can and my ancient (probably single-use) trigger hose. A friend has a manifold and I'll see if that's more effective. As it is, I held the trigger and saw that there was pressure in the can and the hose, but not sure it was getting into the system. Could be the cheapo connector is messed up. Or the low pressure port is jammed somehow.

Planning to clean the port, get a new can of refrigerant, borrow the manifold, try again.
 
A couple things might be going on. Sometimes the cheaper connections to the service port don't depress the schrader core enough to allow the refrigerant to flow. It also can take 5-10 minutes for the can to empty. A set of gauges will probably work better. Also try setting your idle speed up to about 12-1500 rpm.
 
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