A/C clutch engaging and disengaging

[KK]

Got a 94 ranger that on the way home tonight I decide to use the a/c, well it never got cool. Once I got home I noticed the clutch wasn't engaging at all. I got the cheapo refilling deal out and seen that it was right on the lower side of the green area. So I put some more in to get it in the middle, still wouldn't engage. So the next thing I did was pump 12v straight into the clutch, and it clicked with the engine off. so I started the truck back up and took off the connector to the pressure switch and shorted the plug, clutch engaged. Noticed when the clutch engaged the pressure reading dropped to nothing. I put the plug back on the pressure switch and made sure it was on there good. Now the clutch is engaging, pressure is dropping, and clutch is disengaging, the pressure comes back up, and repeat.

What would make the pressure drop when the clutch engages?

 

[Bartman39]

The cheapo refill rig is not telling the truth... The reason the pressure drops when the clutch is engaged is the compressor is pulling suction on the low side which is what your reading... There is not enough freon in the system for the high side to build properly and the cycle to work as it should... Meaning after the high side goes through the orafice tube it drops to a lower pressure but not enough to keep the low side which your reading to be enough to keep the cycling switch engaged to keep the compressor running... But when the compressor cuts off the system starts to equalize and the cycling switch see's enough pressure to make and start the process again...

In short you have low freon in the system still...

But note there is a reason the system became low to begin with... It has a leak so needs to have dye injected and the system recharged then checked a couple of days later with a UV light and glasses to find where the leak is and what needs to be done to fix it...

 

[KK]

There is a cap on the line coming off the compressor that I assume is the high side, as thats the only other cap, and the cheap thing does not fit the fitting. I did notice when I took the cap off that one, that appeared like it was leaking. Sticking my finger over the inlet hole, you could feel the pressure building. I put the cap back on, not sure if the cap and the gasket in the cap is able to withstand holding back the pressure that the high side would reach. I may go out there tomorrow and play around with what ever is in the fitting. I imagine its like a schrader valve on a tire. maybe poking a paper clip will get it to seal better. Anyways, once I put that cap back on tightly, I kept emptying the r134 can until it got to the top of the green area. How long til the refrigerant in the low side makes its way into the high side, I was hesitant to go above the green for fear of screwing something up.

 

[NutBucket]

The only way to properly check the pressure is to get a gauge like this:

http://www.harborfreight.com/a-c-manifold-gauge-set-92649.html

As stated, the low side gauge doesn't tell the whole story.

 

[KK]

I got a pressure gauge like that, but for the houses AC. The ends have screw on connectors as opposed to the snap on like the vehicles have. Do they make some sort of converter for that?

 

[Bartman39]

I got a pressure gauge like that, but for the houses AC. The ends have screw on connectors as opposed to the snap on like the vehicles have. Do they make some sort of converter for that?

Yes but I would not try to mess with it as you can get either type of system contaminated... The one linked to harbor freight would do just fine for most people...

Also the high side schrader valve is a common leak point on 134a systems... You cannot use a reg schrader valve it must be a type that is suited for the high temps produced on the high side of the system... A simple check is make up a little soapy water in a spray bottle and spray the valve(s) Low & High side and see if they are leaking... If so to replace the valves you should recover the freon in the system or have it done...? Then recharge and retest the valves but to note: Be sure to blow all the soapy water out before doing any thing else to the system...

BTW good deal on the gauge kit...:thumbsup:

 

[KK]

No chance to the expansion valve being stuck is there? I don't want to dump money into a truck worth less than repairs would cost. if its something I can jerry rig, even with regard to stuffing the high side schrader valve with jb weld or something like that, anything to stop the leak so the high side can maintain a charge.

 

[NutBucket]

I've always been told the schrader valve really needs a cap to operate properly and that you shouldn't rely solely on the schrader to hold pressure. I'm sure someone will correct me if I'm way off.

 

[Bartman39]

I've always been told the schrader valve really needs a cap to operate properly and that you shouldn't rely solely on the schrader to hold pressure. I'm sure someone will correct me if I'm way off.

Never heard that before...? The caps on 134a systems are made from plastic and do not seal any except to keep dirt & moisture out...


KK... Your first idea about playing with the schrader valve sometimes works to get it to quit leaking, but most of the time its because the seal part of it has gone bad... Please do not put JB weld in it... Back to the idea of capping it I've often wondered why no one has come out with metal caps like when R12 was used...? They would actually seal the port when a schrader valve started leaking and the 134a ports have a better method/type of port for sealing anyhow...?

 

[KK]

Never heard that before...? The caps on 134a systems are made from plastic and do not seal any except to keep dirt & moisture out...


KK... Your first idea about playing with the schrader valve sometimes works to get it to quit leaking, but most of the time its because the seal part of it has gone bad... Please do not put JB weld in it... Back to the idea of capping it I've often wondered why no one has come out with metal caps like when R12 was used...? They would actually seal the port when a schrader valve started leaking and the 134a ports have a better method/type of port for sealing anyhow...?

You would think that somebody out there would make such a thing.

 

[KK]

I was able to get the leak in the high pressure access point to stop. looking into it, there was a little round ball, I poked it with a pen, and got the leak to completely stop. I then used what was left in the 12oz. can I had from before, and what was in a new 12oz. can. From what the gauge is showing it isn't dropping quite as fast therefore it is cycling on and off not quite as fast. It gets up to around 45lbs. and then kicks on, and drops the pressure to 25lbs. at which time the switch turns it off. I need to get another can and put it in and I think it'll be good to go.