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Topic: Air Conditioner runs but won't cool

Posted By: COboondocker on 06/23/15 06:16pm

We have a brand new coleman mach 8 cub and an rv comfort hc coleman mach 7330g335 thermostat. The AC fan runs on both low and high and responds to the thermostat but the air won't cool. For whatever reason the compressor won't kick on. I've checked the yellow wire and made sure it's got a good connection at both the thermostat and at the control box on the AC itself.

It's brand new so we're taking it back for a warranty once we return but we're traveling back through the heatwave in the southwest so I'd like to try to get it working.


Posted By: Chris Bryant on 06/23/15 07:01pm

Compressor not coming on, I would suspect the freeze control- don't know offhand what value they need, but usually either opening or shorting the leads will bypass with no damage.


-- Chris Bryant


Posted By: dougrainer on 06/23/15 08:03pm

Jumping the 2 leads at the Freeze Thermister connection on the control board will start the compressor on a RVP. NOT installing the Freeze Thermister will also NOT allow the compressor to start and run. Did you install the Freeze Thermister? Doug


Posted By: mchero on 06/23/15 09:28pm

Any LED lights on the control board? If so flashing or steady?


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Posted By: COboondocker on 06/23/15 10:48pm

I didn't install the unit but found the freeze thermistor, it's connected to the control board on the other end is just jammed between the fins on the condenser, I was guessing that's not correct but let me know otherwise.

mchero, no lights on the control board I could see from my vantage point. I can try to pull it out completely tomorrow and check. it seemed like the tabs to pull it out didn't want to release and they would break off if I tried to remove it.


Posted By: COboondocker on 06/23/15 10:54pm

i'm tempted to short the leads on the freeze thermistor to see if it works but i don't want to void the warranty or give the impression i am the reason it's not working...


Posted By: dougrainer on 06/24/15 08:15am

adambeck7 wrote:

i'm tempted to short the leads on the freeze thermistor to see if it works but i don't want to void the warranty or give the impression i am the reason it's not working...


The Thermister is installed correctly. Shorting the 2 pins where the Thermister connects will not void your warranty. It takes a few seconds to do that test. just unplug the 2 spades and jump between them. It is NOT 120 volts, it is low voltage dc current. Doug


Posted By: dougrainer on 06/24/15 08:16am

mchero wrote:

Any LED lights on the control board? If so flashing or steady?


You have to remove the control board cover to see any LED lights. Doug


Posted By: Chris Bryant on 06/24/15 08:35am

Unplug it and jump across the terminals- won't hurt anything. That is where the sensor is supposed to be.
You can also check to see if the yellow wire has 12 volts on it (while calling for cool)- if not, it's in the thermostat or t-stat wiring.


Posted By: COboondocker on 06/24/15 11:15am

Didn't work shorting the freeze thermistor didn't help. Don't have a 12v circuit tester.


Posted By: COboondocker on 06/24/15 11:57am

i'll give that shot doug, thanks.


Posted By: COboondocker on 06/24/15 12:15pm

Doug, no LED's but here's two pics of the board itself and the wiring diagram. within the compressor relay the "NO" (black wire) had power but the "COM" (Purple wire) did not.

[image]

[image]


Posted By: dougrainer on 06/24/15 12:41pm

adambeck7 wrote:

Doug, no LED's but here's two pics of the board itself and the wiring diagram. within the compressor relay the "NO" (black wire) had power but the "COM" (Purple wire) did not.

[image]

[image]


The BLACK is the 120 hot feed to the AC board. The Purple goes to the start capacitors. That black box is the relay that CLOSES to supply 120 power to the purple wire. So, If you have it set for COOL and no 120 power to the Purple wire, then the odds are the wiring between the tstat and the control board is open or miswired. It is extremely RARE for a wall tstat to be bad, it is 99% the wiring. It takes 12 volt power to close that compressor relay. In the shop, I would apply 12 volt power to the "Y" spade and see if the relay closes. Before that, I would check for 12 volts on the "Y" feed wire from the tstat. Doug


Posted By: COboondocker on 06/24/15 01:17pm

You're awesome Doug. Thanks. I'll grab a 12v circuit tester and post back.I'll post a pic of the t-stat wiring too. I'm a little color blind so it's tough for me to tell.


Posted By: COboondocker on 06/24/15 03:15pm

[image]

[image]

* This post was last edited 06/24/15 03:45pm by an administrator/moderator *


Posted By: COboondocker on 06/24/15 04:28pm

yellow wire has power leaving the thermostat but not when it reaches the controller box...

* This post was edited 06/24/15 04:36pm by an administrator/moderator *


Posted By: dougrainer on 06/24/15 04:59pm

adambeck7 wrote:

yellow wire has power leaving the thermostat but not when it reaches the controller box...


The yellow wire is open somewhere. USE the unused white wire and connect it instead of the yellow. Also, cut the spade terminal OFF at the AC control box and test the yellow again. Sometimes, they crimp and the insulation stops the copper to spade connection. Or they neglected to strip the yellow before crimping. Doug


Posted By: COboondocker on 06/24/15 05:05pm

finally got it. between switching the two lines on controller board and running a new yellow wire for the compressor to the controller board it worked. thank god, the way home will be MUCH better now.


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