Starcool III Compressor Cycling

[Stormy98]

Working on getting the Starcool system operating in my '98. Replaced the frozen front fan and am now troubleshooting the compressor with the van connected to shore power.

The blower runs fine. At the compressor, there is an an audible click and the compressor starts to run, but after about a second there's another audible click and the compressor stops. This repeats every 20 seconds or so.

I've been through the troubleshooting guide and searched the forums but haven't been able to locate any posts with this specific issue.

At first I didn't understand the necessity of operating the Starcool when the dash AC was running, so I definitely did that on a number of trips. Dash AC still blows cold though.

I opened the electrical box adjacent to the compressor and didn't see any obvious issues with the capacitor, so I'm wondering if that's still the most likely culprit or if there's somewhere else to start first.

 

[Twoxentrix]

First post on this Thread has the manuals for a '95 which member hardwire kindly shared, so I'm just guessing most would apply to what you have as well (page 35 starts the trouble shooting guide):
https://www.sportsmobileforum.com/forums/f20/starcool-ii-manual-and-electrical-system-32386.html

The second Post in that Thread has a link to Manuals that Scalf77 made available as well.

EDIT: This was also an informative Thread started by arctictraveller back in 2020:
https://www.sportsmobileforum.com/forums/f9/starcool-info-26005.html

 

[Stormy98]

Thanks for that, hadn't seen the first thread and while it appears I have Starcool III in my '98 those scans are great. Had already read the second thread all the way through (was very helpful repairing the frozen front fan).

Seems both relays are functioning since the compressor starts vibrating briefly so that's why I suspect the capacitor. Is there a way to test it?

 

[doublevan2]

Stormy 98 - if you find a suitable capacitor please pass the part number on Thanks !

 

[arctictraveller]

I suspect the capacitor. Is there a way to test it?

 

[Stormy98]

Thanks for that, it was just what I needed. Capacitor was bad. Installed a replacement but am seeing the same behavior: there's a click, the compressor starts, then after a second or so there's another click and the compressor shuts off. The process repeats every 10-15 seconds.

The clicking is definitely the AC relay. I put the meter across the lower two terminals of the AC relay (see attached) and it reads 120V with the compressor off. As soon as the relay clicks, the meter drops to 100-105V and then the compressor shuts off and the meter returns to reading 120V.

Two other pieces of info:

1) The replacement capacitor is physically smaller than the original. I had a hard time finding an exact replacement but this one was smaller than I expected. Picture attached.

2) With the capacitor removed but without disconnecting any other wires, I checked for continuity across the various terminals of the relay and they all had continuity with each other. For example, with one lead on the upper right terminal, there was continuity with the other three. Same when testing upper left, lower right, lower left. That seems bad, but I wasn't sure since I didn't disconnect the wires. Can't find any info about the relay so not sure which terminals are the coil and which are the switch, or how to find a replacement.

 

[Scalf77]

be careful with your meter, you are going across multiple voltage systems.

My best guess would be that relay is like this

The control wire is the yellow same as it is manual

I would monitor the 12 control wire to see if the 12 volts stays to keep the relay closed. If it is going away then you need to track backward. It is goes back to the thermostat.

hope this helps.

 

[Stormy98]

The 12V signal is fine - it stays on.

I've got a larger capacitor on order, but in the meantime I'm trying to figure out how the AC relay (contactor?) works. That's what cycles when I energize the compressor with shore power. Wondering which terminals are switched when 120V is applied and also which compressor wire color is start and which is run.

I've labeled the connections in the attached image.

 

[doublevan2]

When capacitor arrives - would appreciate the info on "what - where - cost" if possible - many StCool owners most likely would also appreciate ! Thanks -

 

[Scalf77]

Yes, I forgot about the potential relay. So to the best of my knowledge the potential relay is normally closed relay on the start windings of the motor. When the motor spins up it creates a back emf that energizes that relay removing the start windings and the compressor will continue to run. If that does not open up then I expect there is an overload on the compressor that kick in and takes a way power. Which kind of sounds like what is happening to your unit. I believe the top two contacts in your picture are the two relay controlled terminals, Compressor Yellow and Capacitor Terminal 2. They should be connected when there is no power coming in on the line voltage, once the compressor get's up to speed it should open up.


Here is a pretty good video on the potential relay

 

[Stormy98]

Thanks for the explanation, it makes a lot of sense. I knew the start capacitor needs to be disconnected after the motor spins up but I wasn't sure where it was happening. What's interesting is that the behavior of the system was the same with the broken capacitor and the new one. The new cap arrived today, I'll report back after I've had a chance to test it.

 

[Scalf77]

If the behavior seems the same after replacing the start cap, then maybe it is possible the potential relay is stuck open. Thus compressor would try to start but not have the aid of the start cap, then go into overload shutdown and cycle. You could see if terminal 1 and 2 (Comp Yellow and Cap Term 2) are connected at rest as a check.

 

[doublevan2]

Stormy98 -- not being a mechanic or electrician - I'd appreciate a photo or explanation of where your box with start cap, etc., is located on your van - my van is a 2002 - and I "think" my box containing capacitor is very close to compressor - and facing/up against a frame rail - and NOT easy to access due to the access door actually facing into the frame rail ! Duh - bright idea - NOT !

 

[Scalf77]

So I tried to put the pictures into a schematic form.

 

[Stormy98]

doublevan2 - See attached picture of the electrical box next to the compressor on my '98. Camera is in front of the rear driver's side wheel and is pointing forward. Removal screws are at the top and bottom, angled 45 degrees from the face of the cover.

Scalf77 - Diagram looks great. One note is this type of capacitor does not have positive and negative terminals.

I found this article:

Troubleshooting The Potential Starting Relay

and followed the instructions and got good readings at first - it seemed there was continuity across the switch terminals and an acceptable resistance across the coil. I say "at first" because I was unable to reproduce those readings after removing the relay, although that might have something to do with cracking the case when removing one of the corroded screws with locking pliers. No more continuity across the switch after removal.

Tried looking up a replacement relay but it appears discontinued. Not sure how necessary it is to match the exact model so I ordered one of these:

https://www.supco.com/web/supco_live/products/SUPR.html

I also found what I think is a direct replacement for the original capacitor:

https://www.supco.com/web/supco_live/products/CS340-408X110.html

It's a good match for the dimensions and the capacitance values.

Various pictures attached.

 

[Scalf77]

Updated the schematic, yes the start cap is non-polarized, so no neg or pos terminals.

Looks like the "Universal" potential relay should work.

Good luck with getting this going. I never had issues in this area on my Starcool, so pretty much ignored it. Nice work

 

[Stormy98]

Replacing the potential relay did the trick. It took the compressor a few cycles to start the first time, but now it starts immediately. The $6 capacitor I purchased initially works fine, even though it's physically smaller:

https://www.amazon.com/dp/B0C2KQ1QTL

The original cap was loose in the box so I added a zip tie to the new one to hold it in place.

Getting about a 25 degree difference between input and output air temps.

Thanks to all. Next up, adding a remote fan switch in the dash.