AC condenser fan/compressor clutch relay (99 Tradewind)

[mirage]

The Evans tempcon AC system includes an AC condenser fan/compressor clutch relay that looks like it is supposed to have a fused hot lead independent of the ignition or dash controls (according to the Evans Tempcon wiring diagram). I replaced that relay because both my compressor clutch and condenser fan are not switching on. With the new relay my fan clutch problem persists so I checked each lead on that relay (looking for 12v power) and have found no power. I can't seem to locate any bad fuses on the coach and wonder if anyone knows where that fuse is typically located on this coach or if anyone knows if power to that relay could be switched or interrupted by another devise or condition. (1999 National Tradewind 7371 Cat 300)

Evans Tempcon diagram:

http://www.evanstempcon.com/pdf/ccl/...ic_coolant.pdf

[BFlinn181]

There is often a pressure switch that won't allow 12 v if the coolant pressure is too low. In addition, many systems have a high pressure switch that also stops 12 v power if pressure is too high, as happens for a few minutes after the compressor stops. You might check that those pressure switches are the issue.

[Skip426]

The wiring schematic in the file is much better than the one in the original paper work supplied with my coach , but the dotted lines indicate wiring supplied by the coach manufacturer , so the fuse or 12v Circuit Breaker, could be anywhere. But more than likely in the front of the coach, perhaps on the firewall above the gen set.

A few questions.
Is your coach on a Freightliner chassis? Side or rear rad?
Is the condenser and fan just forward of the front axle?
Have you found the fan and made sure it isn't jammed?
Made sure the compressor isn't seized, by turning the center of the electro-magnetic clutch?
No sense finding and replacing the fuse if it's just going to blow again.

[mirage]

Freightliner, rear radiator, condenser fan is center just forward of front axle, fan is not jammed and turns when external 12v is applied. Center of clutch also turns easily by hand. The tempcom wiring diagram (to me) shows that the relay should have a constant 12v fused lead on pin 30 regardless of the ignition switch position, AC dash controls, pressure switches, or thermostat switch. I think that absence of relay power might be the best place to start?

[Skip426]

Diagram also shows that , condenser fan operation should be independent of compressor clutch, if the thermostat and pressure switch are operational , so the schematic shouldn't be taken as 100% as installed.
So check the relay terminal for power with the key on , before you try anything else.
Then power through the , thermostat and pressure switch, and to terminal 85 on the relay.
Can you supply fused ( 20amp) power to terminal 30 and have things operate?
I'll look at the Freightliner wiring schematic that I have, to see if anything else that might help is apparent .

[mirage]

I will not be able to get back to this for several days but I plan to check for power on relay pin 30 with ignition on. If no power, I will jump 12v power to pin 30 and check for fan and or compressor clutch operation with the engine running and AC on max. If no fan or clutch operation I will move on to the thermostat and the high pressure cut off switch tests. I know where the high pressure cut off is but so far I have not been able to locate the thermostat switch.

[Skip426]

After looking at the chassis schematics, I can tell you this. Only one wire from the relay goes into the main harness, the one that runs the length of the coach to the A/C clutch. The wiring from the relay is a sub harness, and not included in the schematic, the longest wires go to the condenser fan , the other wires from the relay are all under 4 feet in length, the way Newmar hooked up the wiring, both the dash power and the relay power are from the ignition ; through a master ignition relay, and 2, 12v 25amp circuit breakers; because the wiring is so short tracking the wiring shouldn't take long.
I may have a picture of my Evans unit, that shows the thermostat, I'll see if I can post it so you know what your looking for.

[Skip426]

Found some pictures that may help.
First is of the Evans set-up , square box is the thermostat with a tube that runs into the housing.
Second is of the Newmar wiring. The blue wire across the bottom of the picture , that changes to white is the power wire to the A/C clutch.
In my wiring the relay is hidden in the top left of the photo the blue wire runs up to it, The two 12v circuit breakers with red wires, of the 3 that are linked with the aluminum bar, are the A/C dash and A/C relay power.

[mirage]

Thanks for the pictures, your setup is very different than mine but this did help me to ID and locate my temp sensor. Here is an update of my troubleshooting, any opinions or suggestions are welcomed;


I do not ever have 12v on pin 30 on the relay in any condition. I have replaced the relay and have the same condition. I have even applied separate 12v fused power to pin 30 on the relay at which point my condenser fan turns continuously but I still do not get compressor operation in any condition with engine running and AC on max. I do have continuity across the pressure switch terminals as I should. I can't access the location of the temp switch (6 pin connector). I am confused as to where the compressor obtains it's power, is it powered off the relay or off of the dash vacuum switch?

Should my next step be to try to get to the temp sensor (I may have to disassemble the front body of the coach). Should I try to apply 12v power to the compressor?

I am assuming that I could either have a bad temp sensor or a bad compressor clutch (the fuse is good)(The clutch is not frozen as I can spin it manually with my finger when the engine is not running) Is it also a possibility that I have a bad dash vacuum switch even though when switched on it sounds like it is operating the vacuum pump?

[Skip426]

I'll scratch my head and post more in the morning. After looking at my coach again.
I'll double check my wiring, but the power flow should be , dash switch , to the vacuum pump and the temp sensor, from the temp sensor to the pressure switch then to the compressor clutch.
This section of the wiring is competed by the coach manufacturer , so there can be differences, and Evans would have no real say in how the final wiring is hooked up.
If you going to jumper power to the compressor , do so through the pressure switch, so if the refrigerant pressure is low you won't do damage.


Do ANY of the wires to the relay have power at any time , key on , A/C switch on ?

[mirage]

No, never any power at the relay on any pin and in any condition unless I jump fused 12v to pin 30 and then the condenser fan runs regardless of ignition or AC dash controls condition. I am still not clear on the location of the temp sensor and suspect that it might be the problem. Evans tempcon suggested that it might be on my condensor coil but I cannot find it there. I believe that you suggested that it is a "square box" in one of your images with a 6pin micro connector. Evans tempcon believes that is just heater core temp. I do have continuity across the pressure switch and I read about 35psi pressure on the low side so I do not believe that I have a high or low pressure condition and am likely OK jumping 12v directly to the clutch for a very short time just to verify it's operation.

[bdpreece]

Not familiar with your exact coach but when my compressor and fan would not come on I found the problem to be what I think you would call a temp sensor. This was located on the outside fire wall and is nothing more than a switch with a sensor tube that is stuck into the coils to sense whether the ac is freezing up. I jumpered the two tabs of the switch together and everything started working. Of course you can't just leave it jumpered as the unit will freeze up but you can test it that way.

[mirage]

Thanks, I have been trying ti find the temp switch and finally located it in a very hard to reach location that I have to squeeze myself into so that I am standing up between the front fiberglass exterior of my coach and the firewall. I cant even see it and had to reach up blind to remove the two connections, unscrew the sensor one handed and gradually extract the capillary tube also one handed. Once out I tested it and found no continuity across the pins so I know it to be bad. I'm sure this is the problem (certainly a problem) and have ordered a new temp sensor. National made this part nearly imposable to find and just as hard to change out! My only uncertainty is that with that bad temp sensor in the circuit and with external 12v jumped to pin 30 on the relay I was able to get the fan turning but still had no compressor clutch engagement. I expect that replacing this temp sensor will get my fan working without the jump, keeping my fingers crossed that it gets the compressor clutch working also.

[Skip426]

Thanks for the update.
Hope the new part cures your problem.