Chassis Air Condition stopped working - troubleshooting steps. Relay location?

[eXodus]

During my last drip we noticed that the Engine A/C compressor is not coming on anymore. Glad that the Roof A/C can handle the job pinch.

While still out and about I checked all the fuses - but couldn't find anything wrong- pulled them - measure - all good.

When I got home I checked:
- the charge - over 100 PSI on both low and high side.
- both pressure switches have continuity (so the low pressure switch is not blocking it - should be on above 25 PSI)
- the Coil of the compressor has a resistance
- when turning on the Dial to start the A/C there is no power to the plug of the compressor.

I found the troubleshooting steps for the System in Section 1 - HVAC:
http://workhorse.navistar.com/Default.aspx?tabid=574

What I can't seem to find is the location of the compressor relay - is that one  of the 3 ones inside the doghouse on the left? Which one?

[udidwht]

Over 100psi on the low side sounds odd...

What is the resistance on the clutch?

Did you check the air gap on the clutch as well? Too much and it will fail to engage.

[DaveVA78Chieftain]

What I can't seem to find is the location of the compressor relay - is that one  of the 3 ones inside the doghouse on the left? Which one?

Compressor relay location is shown 1999-2003 Section 1 pdf page 13.  There also are other 5.7L location diagrams in this pdf (PDF pages 16/17)

5.7L A/C Section support is provided in Section 6 PDF page 2108

Be sure to check the index pages for topic (eg A/C - 5.7L) for location

[eXodus]

Compressor relay location is shown 1999-2003 Section 1 pdf page 13.  There also are other 5.7L location diagrams in this pdf (PDF pages 16/17)

Thanks,  found the relay    - it's under the doghouse close to the drivers feet.  There are 3 relays and the middle one is the A/C relay in mine - but the wire looms are pretty long and the relays are interchangeable - so anyone working there can put them in any order on the side.

Did you check the air gap on the clutch as well? Too much and it will fail to engage.

I manually bridged the relay and - it works and the A/C compressor comes on. I didn't run it for long - since it bypasses all safety features.

Further I did some more measuring and figured out that the control in the dashboard is doing what it's supposed to do.  It turns on power to the Light-Blue wire when turning A/C lever.



From the diagram - I understand the the PCM is providing the ground to the high pressure - which I tested - it works. It's open when the key is off - and ground as soon as the ignition is on.

But I never get 12V to the High pressure switch at the back of the compressor-  so I assume I got somewhere a loose connection (or another pressure switch/ fuse) from the  "Body Builder A/C control"  to the High Pressure switch.   (right side of diagram)

When I understand the signaling correctly - the PCM waits for the 12V from the high pressure switch to turn on the relay.

[DaveVA78Chieftain]

I am looking at the wiring diagrams in 1999-2003 section 1 and section 6 for 5.7 gas (motorhome) from the workhorse web site. Neither of them reflect the A/C high pressure switch on the left side of your drawing.  Only the one on the right side.  Even the location pics in section 1 only reflect 1 A/C high pressure switch (on rear of AC Compressor).
Your drawing is from the s1-1 Section at the back of Section 1.  Unless your positive you have 2 HI pressure switches I would use the drawings in the front of Section 1.  Even though principle of operation is the same, just be sure your using the correct reference drawing as connections are different.

Anyway, way this works:
Note: when AC system sits idle for a period of time the pressure on HI and LOW side equalizes which is why you had 100psi initial reading.
1. ON/OFF control 12VDC signal from Body builder circuit (thermostat control) is applied to pin A of AC High Pressure Safety Cutoff switch.  The resistor provides the path to ground so that VCM/PCM sees a high/low signal from AC High Pressure switch (AC ON/OFF signal from body builder circuit).
2. This is passed to the VCM (C3 pin 25)
3. VCM orders AC Compressor relay ON by providing a ground path via C3 Pin 1 - Note: this is where differences between your posted drawing and the workhorse drawings I am looking at come into play.
4. As pressure builds up on HI side, Pressure drops on low side (compressor suction) until the AC LOW pressure switch opens (2-9psi). Sensed by VCM C3 Pin 30. (again difference in drawings used)
5. VCM orders Compressor relay OFF by opening ground path to compressor relay.
6. Pressure on LOW side slowly builds back up until AC LOW pressure swtich closes (22-32psi)
7. GO to step 3. 
Step 3 to 7 cycle repeats until Thermostat control opens (requested temp setting achieved (return to step 1) or AC is turned OFF) to High pressure switch.  Compressor clutch should only cycle ON/OFF due to LOW Pressure switch cycling NOT from HIGH Pressure safety switch cycling.

Note A: AC LOW pressure switch opens at 2-9PSI, Closes at 22-32psi.  There has to be enough Freon in the system in order for this switch to close (22-32psi) and allow the AC Compressor Clutch to be turned ON.
NOTE B: Workhorse only provides a partial AC system because they have no control over how the different body builders will implement the interior design. That is why you do not see the interior AC controls, Expansion Valve, Evaporator, etc.  on the Workhorse drawings.
NOTE C: A description of what additional functions the VCM provides during AC operation is listed in Section 6 page 2108.

[eXodus]

Thanks Dave for the explanation. I'm trying to find the right diagram

Your drawing is from the s1-1 Section at the back of Section 1.  Unless your positive you have 2 HI pressure switches I would use the drawings in the front of Section 1.  Even though principle of operation is the same, just be sure your using the correct reference drawing as connections are different.

So I got 3 pressure switches - but I don't know if they are high or low pressure:
 
- Back of A/C compressor (high presumable)
- In one of the fixed aluminum lines (have to trace where that one goes to)
- On top of the Accumulator drier (low presumable) 

For testing - I bridged all pressure switches (one by one) with jumpers and it didn't change anything.

I'm a little suspicious about switch on the accumulator since I'm not getting a good reading on that one. (hard to get to under the hood)  but since when I bridge the plug - nothing happens - not sure.

Thanks Dave for the hint with the Engine module of the Manual:


I've looked at the Diagram you noted on Page 2108 and the part I'm looking at is the same - I'm not getting 12V to the high pressure switch LT Blue - Would you agree there should be 12V while running?

[DaveVA78Chieftain]

No 12VDC at the input to High Pressure switch means the Dash Panel Thermostat/AC ON/OFF switch is not telling the AC system to turn ON.  Also referred to as NO AC Request signal.  No matter which setup you have that is required.

[eXodus]

Ok thanks for confirming,

I've checked the Dash Panel A/C switch and there the Blue Cable is delivering 12V -  so I'm loosing it somewhere in the wire loom going to the High Pressure switch - I've checked for continuity at the connector and none to be found.

Could be just the pressure switch connector - I found lots replacement pigtails online - since they apparently go out more often.  I've had bunch of engine work done a couple of months ago - and now we removed that

So my idea is to run a parallel wire from the dash panel to the high pressure switch connector and see if I get the A/C to turn on.   If that confirms our theory - I'm going to trace the wire loom and see where the connectors from the Bodybuilder to the Chevy P30 parts are and where I got a broken connection.

[eXodus]

After lots of crawling under the dash tracing wires and in the engine bay I finally found component which is causing my troubles.
There is a small component on top of the airbox where the condenser lives.  It gets the 12V from the dash A/C control and then from there it goes to the High pressure switch at the back of the compressor.

The wire going to the "thing" had a weathered label with a printed "AC sense"  on it.  It only has two electric connectors attached.  I've bridge them with a 5A fuse and my A/C running nice again.

It has thin metal pipe attached and when I look up the parts number it says it's a

a46-3122-000 thermostat. Which is now superseded by A46-3122-030
https://www.ebay.com/itm/112336927082

It's $45 and I looks like the sense tube is going into the condenser housing and will be a pain to replace.

What does this thermostat do? It is not part of any electric drawing I could find.

The only reference I could find someone in https://www.rvforum.net/threads/whats-this-ac-part-called.56040/  saying it's against freezing up. I'm in Florida and never drive in cold weather. Is this necessary?

[DaveVA78Chieftain]

What does this thermostat do? It is not part of any electric drawing I could find.

Think in terms of a glass of ice water where condensation builds up on the outside of the glass (warm air on cold surface).
If the condenser temp gets below 32F (0C) then ice starts to form.  The thermo-relay detects the low temp (31F) and opens the circuit shutting down the AC.  Once the condenser temp gets back up to around 39F it closes allowing the AC to turn back ON.  Just a safety device to prevent the condenser from freezing up. Most likely added by RV Mfg.

[eXodus]

Just a safety device to prevent the condenser from freezing up. Most likely added by RV Mfg.

I made a description mistake - its the evaporator housing and not the condenser - the evaporator is the thing which is getting cold - the condenser is warm.

Thanks Dave.

I've ordered the part and should get it in week or two.  I found video how to replace it with minimum effort - might be not as accurate placed as before. but good enough to act as a safety device.

[DaveVA78Chieftain]

LOL - Silly me I should have caught that, Oh well it was the wee hours of the morning.  Good luck

[eXodus]

All good

I've just added the Thermostat-switch to the Wiring Diagram which I have been using for the final diagnosis.

Might help someone in the Future.  But how the A/C system works - the manufacturer could have put the thermostat in series with any of the other switches and achieve the same effect- shut it down when getting to cold.

[eXodus]

I've replaced the Freeze Protection Thermostat 

The new next to the old one-  Was relatively simple to replace

just mark the distance how long the old stick into the airbox - transfer that marking to the new tube
bend the tube straight and fiddle it inside. At some point it stops - probably hitting the evaporator

A/C works nice again.  Waiting for a couple of hot days to take it for a drive and check it's capacity.

Interesting that they opted to add the freeze protection. None of the P30 or Chassis builder A/C system diagrams I looked at have this specified.



But I found pictures of the thermostat on the airbox from the A/C builder.  SCS Frigette Dash Air, Heat - Cool Unit

[Mlw]

Well, as far as I know every AC should have this function.

as dave said
Think in terms of a glass of ice water where condensation builds up on the outside of the glass (warm air on cold surface).
If the condenser temp gets below 32F (0C) then ice starts to form.

With other words, when there is no protection and you would turn on the AC in allready freezing temperatures (I sometimes do when i want to defrost the windshield faster the whole system would freeze solid when you forget to turn it off with all hazards waiting to happen.

[DaveVA78Chieftain]

I have house window AC's freeze up on me especially if I get lazy and allow the air intake filter over the evaporator get dirty reducing air flow.  Same issue. 

[eXodus]

Well, as far as I know every AC should have this function.

Thanks, learning more every day.

Not saying it's unnecessary, just never saw it.  And I took apart many A/C systems in cars, trucks and home.
And never saw a part like this.  Maybe more modern systems are solving the icing issue with other sensors? 
Temperature sensor in the mixing body ? Airflow? Blower current? 

[Mlw]

I have house window AC's freeze up on me especially if I get lazy and allow the air intake filter over the evaporator get dirty reducing air flow.  Same issue. 

That's probably the main reason then why those units are banned in Europe and not seen here. I often wondered about that in the past.

Why US have windowed A/C units where in most of Europe they are banned as either hazardous or simply inefficient

So you see, you learn something every day ;-)

[eXodus]

That's probably the main reason then why those units are banned in Europe and not seen here. I often wondered about that in the past.

1. Reason almost no sliding windows in Europe. Most of them swing inward or outward. No way to mount a Window A/C
2. Since you can't mount them properly - they are bound to fall out of the window and hit someone (Hazard)
3. Electricity is expensive in Europe - Window A/Cs are cheap, but ineffective. So you get a better return on Investment with a split unit.   
4. Mini Split are cheaper in Europe then in North America and far more advanced. Americans get like 15-20 year old tech, the consumer/regulators is less demanding. (cheaper electric and fuel)