Question about Dometic Rooftop RV Air Conditioner

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High cool not working

The low cool and low fan works but high cool and high fan does not work at all. I can here a humm on the roof if I try to turn it on.Whats uo

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  • gitzit1 May 11, 2010

    Do you think it could be a fan capasitor? or is it even worth trying it.

  • Anonymous Mar 22, 2014

    modle#MGHOO55B THE FAN BOWS FOR ABOUT 20 MIN. THEN CUTS OFF AND THE UNITE DOSE NOT TRY TO COOL AND THE LINE DOES NOT FREEZE UP LIKE ITS OUT OF FREON

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  • Master
  • 828 Answers

Compressors on these units runs at only one speed. The change to high cool is only a change in blower speed moving air faster over the cooling coil. I would have the running capacitor for the fan motor checked. A bad capacitor can cause your type of problem. The other problem could be that the high speed winding in the fan motor is bad. Try it operation in the fan only position through the two speeds. If it works in the low and high speed for fan only your problem could be in the selector switch.

Posted on Jun 28, 2008

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Fan is not working on 2001 Chevy Silverado 2500 truck radiator fan motor?


The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
Your best bet would be to take your vehicle to a qualified repair shop !
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My low cool and low fan does not work. High cool and high fan works good. Is this something I can fix myself and if so, how?


If it is a Ford product the problem is with the ignition switch!!!!!!!!High cool function bypasses switch, Other speeds do not.
Your headlights might not be working either.

Jul 29, 2015 | Cars & Trucks

1 Answer

My ac is not working I have a Chevy Tahoe 2005 the fans won't turn on either .


Hi Maria , The A/C system wouldn't keep the fans from running but none working cooling fans will keep the A/C from working ! This is a fairly complex system if your not familiar with this sort of thing ! I will add the description from the factory service manual.
Cooling Fan Control - Two Fan System
The engine cooling fan system consists of 2 electrical cooling fans and 3 fan relays. The relays are arranged in a series/parallel configuration that allows the powertrain control module (PCM) to operate both fans together at low or high speeds. The cooling fans and fan relays receive battery positive voltage from the underhood fuse block.
During low speed operation, the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. This energizes the low speed fan relay coil, closes the relay contacts, and supplies battery positive voltage from the low fan fuse through the cooling fan motor supply voltage circuit to the left cooling fan. The ground path for the left cooling fan is through the cooling fan s/p relay and the right cooling fan. The result is a series circuit with both fans running at low speed.
During high speed operation the PCM supplies the ground path for the low speed fan relay through the low speed cooling fan relay control circuit. After a 3 second delay, the PCM supplies a ground path for the high speed fan relay and the cooling fan s/p relay through the high speed cooling fan relay control circuit. This energizes the cooling fan s/p relay coil, closes the relay contacts, and provides a ground path for the left cooling fan. At the same time the high speed fan relay coil is energized closing the relay contacts and provides battery positive voltage from the high fan fuse on the cooling fan motor supply voltage circuit to the right cooling fan. During high speed fan operation, both engine cooling fans have there own ground path. The result is a parallel circuit with both fans running at high speed.
Do you have a check engine light lit ? The thing to do would have it check at the dealer or a ASE certified repair facility ! They could hook up a advanced scan tool an diagnose fairly quick ! Or you could find a wiring diagram an try testing with a volt meter yourself ! But watch yourself so you don't short out the PCM - engine computer !

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1 Answer

2007 chrysler pt cruiser cooling fan does not work with ac


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1 Answer

Almost no air comes from the ac vents but fan is on high. This happens on auto and also on econ.


The 1992 was prior to Buick putting cabin air filters in so there is not a possibility it is clogged. So more than likely your blower motor is going bad or your fan control switch is bad. Does this problem occur with heating as well as AC? Does it change if you switch between blowing on floor, face, window(defrost) If it doesnt change based on location of blow and type of air temp then I would start by turning fan on high and placing head (ear ) against dash in center of console area. Have someone turn fan knob from low to high with engine OFF...After goign from low to high and back a few times you can see if the blower motor is responding to signal from switch. Listen for a whine, squeal, rattle, or humm. A whine or Humm would indicate a bad blower motor... Squeal or rattle a bad squirrel cage/fan blower blades. If you hear no noise and no perceivable change in blower speed/noise then its possible your switch is bad. Unfortunately the only way to definitely diagnose either is to pull the switch from dash and use multimeter to test for voltage change and for blower motor to pull dash. There is a digital control unit for your car as well. Although rare sometimes the wires on this can loosen or it can go bad. But since you didnt state teh fan wasnt working at all and you are getting cool air, that woudl be teh last thing to check

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1 Answer

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It needs to have the blower motor resistor card replaced.
It still works on high speed because on the high setting the voltage does not go through the resistor.
The resistor is mounted beside the blower motor and is easy to replace.
There you are, thank you for using FixYa.

KL

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