My 1991 isuzu trooper heater blower fan is not working, nor when i turn it to the airconditioner the compressor does not engage. i checked all the fuses except the ac relay fuse block, what could the problem be?

Question edited for clarity. Wrong type of break / brake.
Question moved to model category.

Check the brake switch with a meter first. Then check headlight relays and fuses.

https://www.planetisuzoo.com/threads/no-brake-lights-with-headlights-on-1991-trooper.151493/

https://www.google.com/search?q=1999+Isuzu+Trooper+brake+lights+not+working

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Blower motor fuse - IsuzuPup.com

www.isuzupup.com/viewtopic.php?t=18202

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Has anyone checked the freon charge ?

check that the tap that turns on the heater is working . check that the vacuum line is connected and the heater switch is ok.

It can be issue with faulty motor or its faulty fan control relay.
Bother are to be inspected.Test volt at fan relay and fan motor.-------------
For more help,i suggest you to go through the troubleshooting links mentioned below:-----Click the link below:------

How to replace Cooling Fan on Acura Car models?

http://repairhelpcenter.blogspot.com/2011/11/how-to-replace-cooling-fan-on-acura-car.html
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http://repairhelpcenter.blogspot.com/2011/11/engine-cooling-components-working.html

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http://repairhelpcenter.blogspot.com/2011/11/how-does-vehicles-engine-cooling-system.html

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http://schematicsdiagram.blogspot.in/2012/02/hyundai-sonata-cooling-fan-not-working.html

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http://repairhelpcenter.blogspot.com/2011/10/fuel-pump-relay-and-cooling-fan-relay.html
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http://carbeltrouting.blogspot.com/2011/12/fan-belt-routing-diagram-for-2004.html
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Timing belt, drive belt, serpentine belt, accessory belt, fan belt, engine belt routing diagrams for all types of car models?

http://carbeltrouting.blogspot.in/2012/02/timing-beltdrive-beltserpentine.html
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A/C, heater, defroster fan, not working?

http://technoanswers.blogspot.in/2012/02/ac-heater-defroster-fan-not-working.html
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Blower fan not running on Isuzu trooper?

http://technoanswers.blogspot.in/2012/02/blower-fan-not-running-on-isuzu-trooper.html
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http://repairhelpcenter.blogspot.com/2012/01/how-to-replace-blower-motor-fan.html
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------------These will help.Thanks.

Its very possible the fan clutch has locked up and is now a direct connection from the fan to the water pump.
Depending on if it is controlled by temp or speed, it may not run at full speed when cold or at idle.
When the engine is cold and not running, a normal fan clutch would let you turn the fan blade without turning the pulley.

Blower switch or diode is shot

Motor bushings have worn out or leaves of foreign object is on blower fan. You will need to replace the blower motor

resistor will located with blower switch or blower motor. thanks

heater blower needs to be replaced try a scrap yard very minimal cost