AC system blows cold but clutch stays engaged does not disengage at all.

[olli1]

I have searched this forum and other forums but I just cant seem to find anything on why the ac clutch is staying engage and not cycling like most ac systems do. Im in the process of moving to a different state in the coming weeks. So Ive pulled the fuse for ac system so car transport company wont engage system. Im also in Dallas location for just a little while longer if anybody is near by who wants to come take a look. Otherwise I will be messing with it here and there between packing and twin toddler duties.

Ac charge was way low so I hooked up my gauges and started toping off the charge. Ac started blowing cold again. So using temp chart and scale tried to get the gauge readings in range of chart without adding to much refrigerant. Well little to late I noticed that the clutch is always engaged and it never disengages. I usually run into the clutch wont engage problems but never had a clutch wont disengage. I noticed the sight glass on dryer is full of liquid with ac switch engaged and never leaves the window unless I turn it off of ac. I tried getting into the service manual a little bit but haven’t found anything yet. I swapped relays in engine bay just incase. There was no help and swapped relays back.
The gauges still reading low after 2 cans of just refrigerant only and its blowing cold. Ive ran the car for 10min and clutch just doesnt disengage. I fear maybe its over serviced or if not I dont want to over service it or is the system still low on refrigerant. Also I just dont know what sensor or switch tells the clutch to disegage.

What should I be looking for?
What switch or sensor tells the clutch to disengage?
Is the system still low or overfilled on refrigerant?
Should I just evacuate it all out and start over?

Thanks

 

[Chad Spackman]

I believe compressor clutch uses a high side pressure switch. My own experience with this has been, too low on refrigerant causes no cycling, too high causes frequent cycling. I have a 94, things may be different with later generations. I’m not near my shop manuals at the moment. If no one else chimes in, I will when I’m back home. Take this as an incomplete response. In short, on all the time, might indicate not enough refrigerant or a bad pressure switch

 

[Chad Spackman]

I’m wrong. Looked under the hood and pressure sensor is on low pressure side. So low pressure would turn compressor off. A stuck switch, too much refrigerant, or a bad compressor, could keep pump on

 

[Chad Spackman]

The only other sensor in the system is a temperature probe on the evaporator. This is meant to turn the compressor off when the evaporator gets too cold. I suspect that in a properly charged system. The temp probe is the main source of feedback that would cause compressor on/off cycling

 

[Chad Spackman]

Another addition: the way the system is wired, the dashboard AC switch, the low pressure cutout switch, and the evap temp switch… are all wired in series. So the power train control module gets one signal. If all three switches are closed, the compressor can be instructed to engage. The low pressure switch, and the evap temp probe/switch are both normally closed. One of them could be stuck closed.

The only way to test the pressure switch would be to bleed refrigerant. Which doesn’t sound like a great idea. I don’t how you test the evap switch without removing it and sticking it in your freezer and then confirming that it opens when very cold. In the process you might find the temp probe is no longer in contact with the evaporator or some other obvious thing.

 

[Chad Spackman]

Lastly, the question of which sensor; the low pressure cutout, or the low temperature evap switch, is most involved during normal compressor clutch operation, is the key to knowing what is going on. I guessed earlier it was evap temp. I once again think my guess was perhaps incorrect. I’m going to say it’s the low pressure switch.

If this is true, your issue will be a stuck switch or too much refrigerant. In either case, it would seem to me a debug step would be to vent some refrigerant. Use your refrigerant gauge to monitor pressure with a rag over the place the can would normally be. With AC off you should see a relatively high pressure. With AC on the pressure should drop. You want this to be on the very low end of green if you have no high side monitoring capability. Vent a little at a time. At some point in the process, the clutch should open up and the compressor should stop.

It so happens my 94 is in need of a charge so I’m starting from low refrigerant. My compressor does not turn on. I’ll let you know if I learn anything.

 

[Chad Spackman]

I brought my system up to 27 psi. Once I got over about 10 psi the compressor started. I ran for about about 15 minutes and the pressure never deviated from 27 psi. I’m back to my earlier thinking. It won’t turn off unless cold probe says to do it and that’ll be rare I think. I guess the AC is like everything else on this car. Brute force approach. I wouldn’t give it another thought

 

[GregVP]

One thing you could try before troubleshooting is bring the rpm to 2000 and hold there. When I recharged had same problem this worked for me. Good luck.

 

[Viper Specialty]

Gen-1 & 2 use a Trinary switch on the High side, and a Thermostat. Gen-3/4/5 use a Binary switch on the Low Side, as well as a Pressure Sensor on the High Side, and a Temp probe on the Evaporator.

In general, the Compressor will run when called, unless the system pressure drops too low via Binary/Trinary, the Trinary or Pressure Sensor show a system pressure too high, or the Thermostat interrupts the compressor call for output target being met.

On a hot day at idle, its highly unlikely the compressor will cycle on and off. More than likely it will run continuous unless the RPM is increased and/or vehicle speed/ambient temps are changed.

 

[Chad Spackman]

Viper Specialty, thanks for chiming in. Is there a, most likely spot for a leak? I have to refill once a year. Workable, but I’d like to find the bleed

 

[Viper Specialty]

Viper Specialty, thanks for chiming in. Is there a, most likely spot for a leak? I have to refill once a year. Workable, but I’d like to find the bleed

Use a light, and run over the whole system. You should see oil residue where there is a slow leak. If you find absolutely nothing, its likely the evaporator.

For what its worth, be careful. A slow hidden leak means you are losing both refrigerant and oil, and most recharges are refrigerant only. Be sure to add a little oil each time to be safe.

If you come up empty AND don't want to mess with the Evaporator core, try Red Angel leak sealer. Its the ONLY one that actually works from my experience, and it WILL NOT harm compressors or clog lines and orifices. Most other sealers only help O-Rings, and will do nothing for an Evap or Condenser leak. If you go that route, evacuate the system, add an estimate of missing oil, add Red Angel, and then fill as normal.

 

[olli1]

A lot of good info here to investigate. So my 99 rt/10 has a trinary switch instead of a high low correct? Im in the middle of moving to a different state, so I wont be able to test some of these replies out for a while but when i figure this out I will respond. Thanks chad, greg, and viper s for the info. Also my shrader valve was leaking, so i replaced both shraders and pulled and vacuum for and hour then shut the system and it held perfect vacuum. I left it like that for the move empty. I pulled the fuse so transporter wont turn on ac. but my question is, will that slow leak out of shrader cause oil loss? also will leaving the system empty hurt anything?