Jake
HalfDork
4/12/13 9:55 a.m.
Need to consult the hive mind for a sec:
Trying to at least diagnose the non-op AC in my '98 Ranger. Seems to have coolant in it (checked that first - so no leaks), but the compressor cuts on then off pretty much immediately- so while the AC is switched on in the cab, you hear it cycling on then off again all the time. Does not cool at all - nothing but warm air out of the vents.
Fuse/relay/sensors to check, or are they all buried inside and require system evac to work on? Or am I kidding myself and AC is black magic enough to require pro-fesh-nul intervention?
Either the fan that provides air through the condenser isn't working, the system is undercharged or overcharged, or you have a blockage on the discharge side. Put gauges on it and see what the pressures are.
cdowd
Reader
4/12/13 10:12 a.m.
You need a set of guages. It is almost impossible to tell what is going on without them. I have a cheap set of Hazard Fraught one that have been usefull for the diagnostics on my BMW.
Chris
The pressure cycling switch in those is a bad mark on the system. Sounds like it is bad to me without hooking up any gauges. Jumper the switch to be always on and see if the compressor stays on. If it does, the switch is bad. If it doesn't, there is something else wrong like a bad relay, you can jumper that too, or something as extreme as a bad compressor or compressor clutch.
Ranger50 wrote:
The pressure cycling switch in those is a bad mark on the system. Sounds like it is bad to me without hooking up any gauges. Jumper the switch to be always on and see if the compressor stays on. If it does, the switch is bad. If it doesn't, there is something else wrong like a bad relay, you can jumper that too, or something as extreme as a bad compressor or compressor clutch.
I don't think any of that would produce fast and consistent cycling. Bumping on the high or low pressure switch would, and I suspect the high pressure switch, as cycling would be slower if it was a low pressure switch. It may use a binary or trinary switch also, in which case it is not a low pressure problem.
bravenrace wrote:
Ranger50 wrote:
The pressure cycling switch in those is a bad mark on the system. Sounds like it is bad to me without hooking up any gauges. Jumper the switch to be always on and see if the compressor stays on. If it does, the switch is bad. If it doesn't, there is something else wrong like a bad relay, you can jumper that too, or something as extreme as a bad compressor or compressor clutch.
I don't think any of that would produce fast and consistent cycling. Bumping on the high or low pressure switch would, and I suspect the high pressure switch, as cycling would be slower if it was a low pressure switch. It may use a binary or trinary switch also, in which case it is not a low pressure problem.
Sorry, meant pressure cutoff switch. Got Chrysler on my mind while typing.
Jake
HalfDork
4/12/13 2:13 p.m.
Being the (in)competent mechanic that I am - I guess I need to locate a multimeter for this project - the pressure switches sound like likely culprits, so we'll see what bypass/jumpering them does?
Take the connector off, insert wire to complete the circuit between your two points of contact inside the connector and attempt to operate the system. No multimeter needed.
BTW, the pressure cutoff should be in the AC line on the driver side near the compressor-ish.
i'm fine, but thanks for asking.
The pressure switches are NOT the problem. They are tripping because of a low or high pressure situation. That's what they are there for. If they were bad, the compressor would either not work, would run fine, or it would run until high pressure destroyed it or burst a line or another component. You need to put gauges on it. If you jump across the high pressure switch and run it, the pressure will continue to rise until damage is done. Get some gauges.
Jake
HalfDork
4/12/13 2:57 p.m.
bravenrace wrote:
The pressure switches are NOT the problem. They are tripping because of a low or high pressure situation. That's what they are there for. If they were bad, the compressor would either not work, would run fine, or it would run until high pressure destroyed it or burst a line or another component. You need to put gauges on it. If you jump across the high pressure switch and run it, the pressure will continue to rise until damage is done. Get some gauges.
Also, duly noted. I have a brother in law who's an HVAC tech - are these the same ones you'd use on your house AC? If so, I can bribe him with beer instead of making a trip to buy a cheap set I'll likely never use again, at least any time soon.
bravenrace wrote:
The pressure switches are NOT the problem. They are tripping because of a low or high pressure situation. That's what they are there for. If they were bad, the compressor would either not work, would run fine, or it would run until high pressure destroyed it or burst a line or another component. You need to put gauges on it. If you jump across the high pressure switch and run it, the pressure will continue to rise until damage is done. Get some gauges.
Disagree, but I digress. Have fun!
In reply to Jake:
No, they are different then home use gauges.
Ranger50 wrote:
bravenrace wrote:
The pressure switches are NOT the problem. They are tripping because of a low or high pressure situation. That's what they are there for. If they were bad, the compressor would either not work, would run fine, or it would run until high pressure destroyed it or burst a line or another component. You need to put gauges on it. If you jump across the high pressure switch and run it, the pressure will continue to rise until damage is done. Get some gauges.
Disagree, but I digress. Have fun!
Well then maybe you can explain how a bad pressure switch will make the compressor cycle at a high frequency. Maybe you know something I don't?
