Basment a/c

madred · 03-02-2012, 07:23 PM

I have recently purchased a 2005 Vectra and the basement a/c is new to me. The thermostat does not seem to be working correctly, in that if I set it for say 74 it does not turn off, even when the temp gets to 72. If I move it to 75 it does not turn on, even when the temp gets to 77.

Also when we go to bed we like to make it colder, so we set it to 62 the other night and it worked for 5 minutes then turned off. I let it set for awhile and it came back on and seemed to work great but after a few hours it stopped. Then it came back on but only for a few minutes before turning off again. When I check the thermostat to see what the temp was, it showed only 67. Is this normal?

KIX · 03-02-2012, 08:02 PM

Assuming you have the typical Coleman-Mack tstat you have three slide switches at the bottom front of the tstat. The left one will control the indoor fan and can be set at Auto or ON. The right side switch is either high or low. always have it on high while using cooling. The middle one is most likely the culprit. It has 4 positions.....Cool - off - gas heat - elect heat. Remove the cover of the tstat then lift off the switch black slider. Spray some electronics cleaner (Radio Shack) where that switch slides. Work the switch back and forth several times. This MAY fix your problem.

KJD · 03-02-2012, 09:44 PM

Doing what " Kix" said should cure your problem but..... there is always a but huh...... I had a wire come loose inside the control box. I took it off the wall 2 screws and one of the wires on the back side where it connects to the wiring on the coach was not pushed in all the way. It was on but not not on right if you know what I am trying to say. I pushed it all the way in and heard a click and mine was good to go from then on. You might check that also if it still is giving you problems.

hdmoxness · 03-03-2012, 02:31 AM

That 4-position slide switch was our problem, too. We’ve had to “fiddle” with the original thermostat for a couple of years, especially in the Elec Heat (heat pump) position. “Cleaning” the switch (it is open and accessible if you pry the thermostat cover off with a fingernail) was some help, but we finally tired of messing with it and just changed it a couple of days ago. Replacement Coleman-Mach stat works great!

As KJD says, check your connections, and be sure the stat is exposed to general air circulation (not a direct draft from a vent, or blocked by a closed door) through your coach. Besides the switch, the stat also contains most of the intelligence that controls your comfort, hot or cold. $107 from RV Plus online. Good luck.

madred · 03-03-2012, 07:05 AM

Thanks, I will try the thermostat. It is strange that moving it one degree up or down does not work as it should. It seems to have problems with determining the temp inside the coach.

KIX · 03-03-2012, 02:33 PM

Quote:

Originally Posted by madred

Thanks, I will try the thermostat. It is strange that moving it one degree up or down does not work as it should. It seems to have problems with determining the temp inside the coach.

If it actually displays the correct room temp but will not power up to achieve the set temp with even a 1* difference then the problem is most likely in the tstat. If it still doesn'l work satisfactorily after trying the cleaning then a new tstat is in your future.

All that is assuming it does start, run and cool sometimes.

madred · 03-04-2012, 12:04 PM

That is were I am confused! The four position switch works in all four modes. The problem is the thermostat sensitivity is not good, we have digital indoor/outdoor thermometers in the coach that are very accurate. the thermostat will continue to run even after the temp (say 74) has been reached, sometimes by 2 or 3 degrees. And if I move it up one degree (to 75) then it will not come on until 78 or so. When the other thermometers are reading 78 the thermostat will still be reading 75. The other problem is when we set the reading to a low setting say 62 (when we go to bed) it will run for a short time then turn off at a high reading say 73 (well short of the 62 setting) then after a time will come back on and act like it is work fine. Then during the night it will turn off again and start coming on and running for 5 to 10 minutes then turn off again. The temp will be something well about the 62 setting. I still think it might be the thermostat but I am not sure, it could be freezing up due to the low setting? Could it be low on refrigerant?

KIX · 03-04-2012, 08:07 PM

The basement units do not have connection points to attach HVAC gauges to unless added after-market. So the only way I know for you to check to see if refrigerant is adequate is to turn the unit on and set cooling to at least 5* lower than room temp. Do this with your generator as power. Watch the amp gauge and when the amps are at 35 - 30 (with only the A/C on) then you can be pretty sure both compressors are running. Check temp of air at return air plennum. Then check air temp at first supply register. There should be approx. a 20* difference if refrigerant level is adequate.
But, to answer your question, low refrigerant will not cause the symptoms you have. A faulty tstat will cause those symptoms.

HD4Mark · 03-04-2012, 08:23 PM

We replaced our Coleman Mach/True Air thermostat after we determined that it read 5 degrees higher than the actual temp. It also had difficulty starting the second compressor according to the HVAC guy that helped me with it but I couldn't swear to that. The new one although expensive as thermostats go works much better.

MntDriver · 03-05-2012, 08:19 AM

What was the outside ambient temp?

We like it cold inside also, and if the outside ambient temperature is lower than what we set the thermostat on, the unit clicks off. It did this until we moved the outside coil thermister to the inside of the coil. All the units we tried (in the dealer's lot did this).

So to reiterate, if your set point is 65 degrees, and the outside ambient temp. is below 65 degrees, your unit wont run....there is nothing wrong with your thermostat.

FrontrangeRVer had some good posts on this issue on this forum several years ago.

Hoghead · 03-05-2012, 03:32 PM

Quote:

Originally Posted by HD4Mark

We replaced our Coleman Mach/True Air thermostat after we determined that it read 5 degrees higher than the actual temp. It also had difficulty starting the second compressor according to the HVAC guy that helped me with it but I couldn't swear to that. The new one although expensive as thermostats go works much better.

Okay, so what brand/model did you get?

hdmoxness · 03-05-2012, 04:28 PM

Here's the one I used, along with instructions to make a required minor wiring adjustment. The OEM thermostat in our coach was a 6535-335; we replaced it as recommended with a 6535-3442.

https://www.makariosrv.com/products/...-True-Air.html

It's a pleasure to have all the HVAC working nicely without our detailed attention all the time. Hope this helps.

HD4Mark · 03-09-2012, 06:54 AM

Quote:

Originally Posted by hdmoxness

Here's the one I used, along with instructions to make a required minor wiring adjustment. The OEM thermostat in our coach was a 6535-335; we replaced it as recommended with a 6535-3442.

https://www.makariosrv.com/products/...-True-Air.html

It's a pleasure to have all the HVAC working nicely without our detailed attention all the time. Hope this helps.

We did the same and also bought ours from Makarios. They are very helpful if you need any assistance with the install.