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| a/c compressor not engaging [message #345140] |
Thu, 11 July 2019 14:36  |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
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Back again. My dash a/c got up and running last summer. (Ran great! Cold knees  ) We recharged with R12a since it was empty. I'm in Canada plus it had been converted to 134 in a previous American life so the fittings were compatible. This summer though, no cold. Checked the low side static pressure and it is sitting at 32 psi. I don't have a gauge for the high side (yet) so i don't know where that sits right now. Low side static I believe should be sitting somewhere in the 70's? So when I turned the coach on and turned on the a/c, I was expecting it to drop. It didn't move. I think I hear a bit of a clicking when I turn on the a/c but I'm pretty sure the compressor isn't engaging. Have to stick my head into her to check for sure. But in the meantime...
Question here is, what would you consider a low enough low side static pressure that the compressor won't engage simply because it is too low on refrigerant? If the compressor doesn't engage, then that static pressure won't change when I "turn on" the a/c, correct? I have a recharge kit for the R12a and am happy to top it off. But thought I would run it by you folks first and see what your educated opinion is. Would it hurt to add a half can of the 12a to bring that pressure up and see if that does the trick?
I know there are a myriad of things that it could be, but thought I would start with one of the things I could possibly address myself without too much difficulty. Or am I so far off the mark I should turn around and hang my head.
Don't want to wander around blindly throwing things at it without some 2nd, 3rd and "n"th opinions.
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: a/c compressor not engaging [message #345144 is a reply to message #345140] |
Thu, 11 July 2019 15:02  |
lqqkatjon
Messages: 2324
Registered: October 2010
Location: St. Cloud, MN
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Deb-
There is a low pressure switch. Easy to access from right in the hatch. It is kinda a dumb switch in you can pull the connector and use a jumper or paperclip to go accross
The wires in that connector. If you do that you will hear/see the clutch kick in. That will tell you if a low pressure is not making the clutch kick in. Many times you jumper
That connector when you first add refrigerant. To get it to start pumping.
Jon Roche
75 palm beach
EBL EFI, manny headers, Micro Level, rebuilt most of coach now.
St. Cloud, MN
http://lqqkatjon.blogspot.com/
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| Re: a/c compressor not engaging [message #345146 is a reply to message #345144] |
Thu, 11 July 2019 15:34 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
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lqqkatjon wrote on Thu, 11 July 2019 13:02Deb-
There is a low pressure switch. Easy to access from right in the hatch. It is kinda a dumb switch in you can pull the connector and use a jumper or paperclip to go accross
The wires in that connector. If you do that you will hear/see the clutch kick in. That will tell you if a low pressure is not making the clutch kick in. Many times you jumper
That connector when you first add refrigerant. To get it to start pumping.
That did it Jon! Thank you. And in perusing the maintenance manual - I found the cut-off pressure - 37psi. When the low end drops below 37psi, the compressor will shut down.
Excellent! Now when the rain stops (again) I'll go out and recharge her! We're all tired of the rain here but the more it rains, the longer it takes for the forest fire season to start!
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: a/c compressor not engaging [message #345149 is a reply to message #345146] |
Thu, 11 July 2019 17:34 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
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Next question... She's now running & running, and blowing cold air, but I have a 'click'. https://ln.sync.com/dl/c481a66c0/636jbyh8-w3ewbbv3-qra8njpf-fczgdxg4
Definitely coming from the front hatch. Thermostat? Relay? Sounds like a switch opening and closing, and when it does, the low side pressure fluctuates (drops a bit then back up). Sounds more like it's coming from behind the evaporator, inside the blower housing? More likely then the thermostat?
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: a/c compressor not engaging [message #345153 is a reply to message #345149] |
Thu, 11 July 2019 20:40 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
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Possibly the low ambient thermostat in the evap section. When this opens due to too cold a temperature of air leaving the evap coil it will cycle the compressor off till the air warms up then the compressor will reingage.. what is the low side suction pressure? You probably need to add more refrigerant to the system too keep the compressor from short cycling and possibly icing up the coil.
Roy Keen
Minden,NV
76 X Glenbrook
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| Re: a/c compressor not engaging [message #345154 is a reply to message #345153] |
Thu, 11 July 2019 21:10 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
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Hi Roy. Low side static is at 70psi. Running drops to about 40ish but goes up to about 45-50 and down again as the switch repeatedly opens and closes. It never settles at one pressure. So I don't really know exactly what the running pressure is. I did find in the manual that the low pressure switch wants it above 37, so anything less than 40 would be getting pretty close to low end acceptable.
It is possible Im still running with too little refrigerant but the static low side is at 70 which I think should be pretty close to where it should be. I'm running the R12a and I'm checking into whether that should affect my static pressure in this system. I know 37 is bottom limit for the compressor to run (thats in the switch). But I have to find what the static pressure should be. Still going through the manual. Don't want to overfill it but don't want to freeze things up either.
I'll take another look at it tomorrow. If it is that switch, what is more likely - problem with the expansion valve or the switch itself? Any good way to determine where the problem lies?
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: a/c compressor not engaging [message #345155 is a reply to message #345154] |
Thu, 11 July 2019 22:02 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
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Dug a bit deeper and that click seems to coming from close to or at the front of the compressor. It does sound like a switch opening and closing. Very obvious when I open up the engine cover, but cant quite locate it. I'll look more closely tomorrow with a flashlight. Meanwhile checking in the maintenance manual for something that might correspond to what I'm hearing and seeing in the pressures.
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: [GMCnet] a/c compressor not engaging [message #345158 is a reply to message #345154] |
Thu, 11 July 2019 23:16 |
emerystora
Messages: 4442
Registered: January 2004
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Can you please clarify exactly what refrigerant you are using. You say R12a but is this Freon 12 or is it HC12a? It makes a big difference in pressures.
Emery Stora
77 Kingsley
Frederick CO
> On Jul 11, 2019, at 8:10 PM, Deb McWade via Gmclist wrote:
>
> Hi Roy. Low side static is at 70psi. Running drops to about 40ish but goes up to about 45-50 and down again as the switch repeatedly opens and closes.
> It never settles at one pressure. So I don't really know exactly what the running pressure is. I did find in the manual that the low pressure switch
> wants it above 37, so anything less than 40 would be getting pretty close to low end acceptable.
>
> It is possible Im still running with too little refrigerant but the static low side is at 70 which I think should be pretty close to where it should
> be. I'm running the R12a and I'm checking into whether that should affect my static pressure in this system. I know 37 is bottom limit for the
> compressor to run (thats in the switch). But I have to find what the static pressure should be. Still going through the manual. Don't want to
> overfill it but don't want to freeze things up either.
>
> I'll take another look at it tomorrow. If it is that switch, what is more likely - problem with the expansion valve or the switch itself? Any good
> way to determine where the problem lies?
> --
> Deb McWade
> Logan Lake, BC, CAN
> "Li'l Sister"
> '77 Kingsley, 403, EBL EFI;
> TZE167V101404
> It's Bigger on the Inside!
>
>
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| Re: [GMCnet] a/c compressor not engaging [message #345160 is a reply to message #345158] |
Fri, 12 July 2019 00:00 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
Karma: 2
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emerystora wrote on Thu, 11 July 2019 21:16Can you please clarify exactly what refrigerant you are using. You say R12a but is this Freon 12 or is it HC12a? It makes a big difference in pressures.
Emery Stora
77 Kingsley
Frederick CO
Hi Emery. Up here we call it R12a. Lots of suppliers since its a legal conversion directly from R12. We don't have to go through the R134 conversion. Same as Duracool. It is a straight hydrocarbon so probably what you are calling HC12a? Not Freon or R12 that was originally in these machines.
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: [GMCnet] a/c compressor not engaging [message #345161 is a reply to message #345160] |
Fri, 12 July 2019 00:46 |
roy1
Messages: 2126
Registered: July 2004
Location: Minden nevada
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The switch I believe you are referring too is the loss of charge switch it should be located in the liquid line not the suction line. It would be best to have a set of gages on the system and jumper out the loss of charge switch then add refrigerant till the low pressure gage reads about 25# with the engine rpm around 1500. I suspect you may have a fair sized leak if the loss of charge switch is shutting off the compressor.. it will be easer to diagnose the problem with the switch jumped and the high and low pressure readings with the engine running.
Roy Keen
Minden,NV
76 X Glenbrook
[Updated on: Fri, 12 July 2019 00:52] Report message to a moderator |
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| Re: a/c compressor not engaging [message #345163 is a reply to message #345140] |
Fri, 12 July 2019 06:06 |
Chris Tyler
Messages: 458
Registered: September 2013
Location: Odessa FL
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Id recomend getting a set of gauges as well. Otherwise you are shooting blind, and 12a doesnt like overcharge.
Harbor frieght has a decent set. You may need adaptors depending on your fittings, and a can tap to attach.
76 Glenbrook
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| Re: [GMCnet] a/c compressor not engaging [message #345191 is a reply to message #345170] |
Fri, 12 July 2019 13:59 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
Karma: 2
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Hello all. I do have a gauge in the recharge hose so I have been able to note the low side pressures. Problem was that with the compressor toggling on & off repeatedly every couple of seconds or faster, I never got to a steady running pressure yesterday. It was continually flipping between running (when it the gauge would start to drop and then right back into non-running, when the gauge would start to climb again). That was why I couldn't determine a running pressure. I only put 1 can in yesterday since it was reading '0 psi' running once I bypassed the low pressure switch. It was after that I got the oscillating on/off and fluctuating low side pressure - because I had reconnected the switch. The reason I was asking earlier about static pressures was because not knowing exactly how much refrigerant was remaining after my winter loss, and the inability to get a running pressure, the only thing I had was the static pressure to go from.
This morning I tried first by-passing the switch. The clicking disappeared. It was running at 10 psi, so I slowly added one can. The thermostat was toggling on & off every minute or so. Got the running pressure at 18-20psi.
Cold air inside, but then I thought I heard a hiss coming from the line coming out of the evaporator and thought I felt a leak at the threaded connection. Wasn't there yesterday. Pressure started dropping very slowly. I went inside to get my "bubble bottle".
Came back out - no hiss, no bubbles. But also the tube coming out of the receiver was no longer cold though it was still cold at the evaporator. Seems like the compressor shut off and so did the flow of refrigerant. The low pressure switch was still by-passed.
Went inside the coach and was getting a smell from the vents. I turned off the a/c. Rechecked back outside, no leak no hiss. Back into the coach and turned the blower onto vent - no blower. I no longer have any blower with vent, heat, defrost or a/c 
I have reconnected the low pressure switch. Waiting to see if something has over heated due to coolant loss (probable leak), the lack of flow (freeze up?) and the by-passed switch, and some internal breaker might reset once it sits and cools off. My feeling is probably not. My luck won't be that good.
Just went out and checked - still no blower. Blower relay? There is a faint smell of hot plastic/rubber in the hatch.
Smell is coming from the blower motor. Just checked and the blower works (went straight from battery to hot connector and she fired right up. Thanks Rob  ). So... somewhere between A & Z. The blower itself might want to be replaced. I may pull it (give it a try) and see what kind of shape everything is in there. This is the second time I have had a burned out 'something' this summer related to the blower. Perhaps it's pooped and the everything else needs to work too hard to push it. Dunno. Give it a clean out, see if it turns freely. Maybe replace it, or brushes?. We'll see. But first have to figure out where the current 'no run at all' problem is coming from. I no speeds at all, with a/c, heater, vent or defrost.
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
[Updated on: Fri, 12 July 2019 15:05] Report message to a moderator |
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| Re: [GMCnet] a/c compressor not engaging [message #345195 is a reply to message #345191] |
Fri, 12 July 2019 17:01 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
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Well, fuse is fine (tested) fusible link looks OK. Tomorrow when its cooler in there I'll grab the meter and start checking circuits.
Right now, the a/c is taking a backseat.
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: [GMCnet] a/c compressor not engaging [message #345196 is a reply to message #345195] |
Fri, 12 July 2019 18:10 |
6cuda6
Messages: 975
Registered: June 2019
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Sounds like you may have lost the blower motor resistor.... its what gives you the speeds. If something in the blower box hit it (like a twig, rodent etc) it usually gives up the ghost and since the blower motor runs with direct power it would be the next logical component to verify.
Rich Mondor,
Brockville, ON
77 Hughes 2600
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| Re: a/c compressor not engaging [message #345212 is a reply to message #345140] |
Sat, 13 July 2019 02:14 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
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HI Deb. This is meant as a compliment. You can not believe how great it is to have someone here giving complete on topic information when requesting help. I have not commented on this thread because everybody here has been giving you good responses.
I agree that you have two different problems and that you need to fix the blower problem first. A couple of comments on the blower motor problem and you may already know this.
There are two different power sources for the blower motor. The first is through a 25 amp fuse and it supplies voltage to the blower motor through the fan switch and the blower motor resistor for all speeds EXCEPT the highest speed. In the highest fan speed this same circuit powers the fan relay coil.
Energizing this relay coil changes the power for the blower to a different power source. This source is a wire with fusible link direct from the center terminal of the isolator which is effectively direct from the alternator. So in the high speed fan switch position power from the 25 amp fuse will energize the relay coil (you can feel it if you hold the cover while someone else moves the switch to high and back) but if the engine alternator is not running, then no power will be applied to the blower motor from the isolator / alternator connection.
So if all speeds fail suspect the 25 amp fuse.
If only high speed fails WITH THE ENGINE RUNNING suspect the high speed wire, or the inline fusible link (not the one on the relay) or fuse, or relay, or burned connections which are very common.
If only one or more low speeds fail but high speed works, suspect the fan resistor, or fan switch, or again a burned connection on either or these or the fan relay.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
[Updated on: Sat, 13 July 2019 13:23] Report message to a moderator |
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| Re: [GMCnet] a/c compressor not engaging [message #345216 is a reply to message #345212] |
Sat, 13 July 2019 06:41 |
Ken Henderson
Messages: 8726
Registered: March 2004
Location: Americus, GA
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And don't forget the unreliable ground connection of the motor through a
single jumper to the motor's mounting flange.
Ken H.
On Sat, Jul 13, 2019 at 3:14 AM Ken Burton via Gmclist <
gmclist@list.gmcnet.org> wrote:
> HI Deb. This is meant as a compliment. You can not believe how great it
> is to have someone here giving complete on topic information when requesting
> help. I have not commented on this thread because everybody here has been
> giving you good responses.
>
> I agree that you have two different problems and that you need to fix the
> blower problem first. A couple of comments on the blower motor problem and
> you may already know this.
>
> There are two different power sources for the blower motor. The first is
> through a 25 amp fuse and it supplies voltage to the blower motor through
> the fan switch and the blower motor resistor for all speeds EXCEPT the
> highest speed. In the highest fan speed this same circuit powers a the fan
> relay coil.
>
> Energizing this relay coil changes the power for the blower to a different
> power source. This source is a wire with fusible link direct from the
> center terminal of the isolator which is effectively direct from the
> alternator. So in the high speed fan switch position power from the 25
> amp fuse
> will energize the relay coil (you can feel it if you hold the cover while
> someone else moves the switch to high and back) but if the engine
> alternator is not running, then no power will be applied to the blower
> motor from the isolator / alternator connection.
>
> So if all speeds fail suspect the 25 amp fuse.
>
> If only high speed fails WITH THE ENGINE RUNNING suspect the high speed
> wire, or the inline fusible link (not the one on the relay) or fuse, or
> relay,
> or burned connections which are very common.
>
> If only one or more low speeds fail but high speed works, suspect the fan
> resistor, or fan switch, or again a burned connection on either or these or
> the fan relay.
> --
> Ken Burton - N9KB
> 76 Palm Beach
> Hebron, Indiana
>
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Ken Henderson
Americus, GA
www.gmcwipersetc.com
Large Wiring Diagrams
76 X-Birchaven
76 X-Palm Beach
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| Re: [GMCnet] a/c compressor not engaging [message #345232 is a reply to message #345216] |
Sat, 13 July 2019 11:23 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
Karma: 2
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Hi Ken. Thanks for the crash course! I wasn't aware that there were two power sources for that fan. I just went down to check the high speed fan since that was something I could easily do BEFORE my morning coffee (after I got that weird smell I couldn't remember if i had tested the fan with it running or just in acc). No joy. No fan at all even running. Though it was blowing when I initially got the smell and therefore turned it off. Won't come on again.
Yesterday I pulled that 25A fuse from the panel and it checked out fine on my MM. But I haven't gone point to point with my test light. And haven't looked at the fuse panel itself. So that is next on my list. And Rich (say Hi to Ontario for me), I will check that resistor, as well as pull the motor to see what was going on there that gave me the hot plastic/overheated wire smell from the blower at the end of it all. Something overheated inside that housing.
And Ken H, when I checked the motor directly from the battery, I connected my jump wire right at the connection at the motor housing. But it's possible there's no power getting to it. I'll check that line from the relay to the motor next as well as look at the actual connection. It's another 45 year old spade connector.. I didn't look at the ground. It seemed pretty solid when I last looked at it (June, when the blower quit the first time) but I'll give it a good look this morning.
Even if I do (that's negative)... When I find the problem, I still have to figure out why. I have had 2 issues now with the blower this summer. Overheated & fried one of those plastic OEM connectors in the power line to the motor (the main one with the condenser), and now this. I don't know if this incident and the a/c are related, or coincidental. But I don't think pulling the motor out and giving it a look see and a cleaning could hurt!
But... Coffee and walk the dogs first. Then I can devote my day to test lights and perusing the manual. I have more pieces of paper book-marking pages than I can count right now. I have 2 weeks to get this sorted before I head to Bellingham. Manny tranny on the way!
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
[Updated on: Sat, 13 July 2019 11:26] Report message to a moderator |
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| Re: [GMCnet] a/c compressor not engaging [message #345241 is a reply to message #345232] |
Sat, 13 July 2019 16:38 |
Deb
Messages: 349
Registered: October 2016
Location: Logan Lake, BC
Karma: 2
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Found the in-line fusible link (was what I thought it was, floppy, soft green insulation, 18 ga if I'm reading it right. I can see why some folks might feel inclined to replace it with a fuse. Just looks like it's at the end of its life) and it is intact. Insulation is intact anyway. Have checked the 25A fuse in the glovebox, and it is good (checked it 3 times, flicked it, shook it, checked out all 3 times).
Now this may sound stupid, but bear with the electrically challenged  ... Is the panel flowing current both in acc and running? Or just when the engine is running? Cause when I pulled the fuse and checked for current across the clips I got a light when the engine was running, but not when ignition was in acc. Fuse panel is working from the alternator? Acc is working off the battery? I was wanting to make sure that there was actually current going across the fuse. Perfectly intact fuse means nothing if there's no current for it to carry, right?
The main power wire from the relay to the motor (directly off the battery) is OK. Pulled the top of the dash off yesterday and just checked the fan speed switch now. With the ignition in acc power coming into the switch (brown wire if I'm reading the diagrams correctly) and going out the other connections (blue &?) but not the orange (which I believe is the High), but all 3 outgoing wires light up when the ignition is running. So looks like the fan speed switch is OK. That's as far as I've got. Currently taking pictures of the wiring diagrams (too small for my eyes) so I can check the circuits based on colour, what's going where in the relays and the resistor (though the easiest way to check the resistor is probably to take it out!).
This is going to be a longish process me-thinks. Glad I have a couple of weeks. Should learn a lot about the wiring, basics at least. Let me know if I'm off on a tangent or misinterpreting something. 
Deb McWade
Logan Lake, BC, CAN
GMC Alumnus
It's Bigger on the Inside!
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| Re: [GMCnet] a/c compressor not engaging [message #345251 is a reply to message #345241] |
Sat, 13 July 2019 23:48 |
Ken Burton
Messages: 10030
Registered: January 2004
Location: Hebron, Indiana
Karma: 10
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Deb wrote on Sat, 13 July 2019 16:38Found the in-line fusible link (was what I thought it was, floppy, soft green insulation, 18 ga if I'm reading it right. I can see why some folks might feel inclined to replace it with a fuse. Just looks like it's at the end of its life) and it is intact. Insulation is intact anyway. Have checked the 25A fuse in the glovebox, and it is good (checked it 3 times, flicked it, shook it, checked out all 3 times).
Now this may sound stupid, but bear with the electrically challenged ... Is the panel flowing current both in acc and running? Or just when the engine is running? Cause when I pulled the fuse and checked for current across the clips I got a light when the engine was running, but not when ignition was in acc. Fuse panel is working from the alternator? Acc is working off the battery? I was wanting to make sure that there was actually current going across the fuse. Perfectly intact fuse means nothing if there's no current for it to carry, right?
The main power wire from the relay to the motor (directly off the battery) is OK. Pulled the top of the dash off yesterday and just checked the fan speed switch now. With the ignition in acc power coming into the switch (brown wire if I'm reading the diagrams correctly) and going out the other connections (blue &?) but not the orange (which I believe is the High), but all 3 outgoing wires light up when the ignition is running. So looks like the fan speed switch is OK. That's as far as I've got. Currently taking pictures of the wiring diagrams (too small for my eyes) so I can check the circuits based on colour, what's going where in the relays and the resistor (though the easiest way to check the resistor is probably to take it out!).
This is going to be a longish process me-thinks. Glad I have a couple of weeks. Should learn a lot about the wiring, basics at least. Let me know if I'm off on a tangent or misinterpreting something.
Deb, the previous posting was to tell you how the circuit works. Now let's trouble shoot it. First I believe that the green floppy wire that you found is indeed the flexible link. It is designed to burn in half if there is a sustained over load unlike most fuses that will blow immediately on any current flow that exceeds it's rating. (They do make slo-blo fuses) If the wire does burn in half, I would replace it with another of the same size and forget using a fuse.
Here is how I would trouble shoot this. Am Ohm meter works most times, but it will fail occasionally because you are not reading things in their failing condition. As an example a fuse can read good on an ohm meter but open up when current flows through it. I have seen this many times. Also if the fuse holder is not making a good connection you will not catch it reading the fuse with an ohm meter.
So I would now suggest that you check circuits with a volt meter or a test light. The procedure for using wither one is the same:
1. Connect the negative lead of the voltmeter or the alligator clip on the test light to a good ground. Engine battery negative terminal, or the aluminum plate that the isolator is mounted on, or inside the aluminum plate that the gauges like speedometer is mounted in are all good ground sources.
2. Put the circuit in it's failing condition (Key on and fan switch on in this case) and start reading the various components in the circuit looking for absence or presence of approximately 12 Volts DC.
3. Based on knowledge or the wiring diagram start probing the various items (Fuse - both sides, Motor connection , fan relay, delay relay if equipped, fan switch, etc. looking for where the voltage loss is. Once you have found the loss you can more closely look in that area only for why it is missing.
Ken Burton - N9KB
76 Palm Beach
Hebron, Indiana
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