Overheating where is the relay switch - 1994 Isuzu Rodeo

It may indeed be the relay overheating, which could mean the relay is bad, or that the dimmer switch or headlamp switch is bad and drawing too much current, or that the headlamp ground circuits are bad, or that a bulb has a cracked filament so drawing too much current. Why not use an amp gauge to see what is going on. FWIW, I think your relay is on the radiator support, driver's side upper.

Relays go bad, rarely. But it sounds like you already fixed this problem, now replace the bad relay ($25) and HVAC should work too?

What relay switch are you talking about, and how is the engine overheating ?

I have fixed my own 2002 Jeep Cherokee twice for the overheating issue. Overheating can be caused by a number of different problems, but one of the most notorious problems for the Jeep is the 'radiator fan relay switch'. When the temperature thermostat goes over 210, it tells the relay switch to turn on the radiator fan to cool down the engine. If that relay switch isn't working, the fan never turns on and thus your engine overheats. Here's a simple test to check if this is your overheating problem:
1. Start up your Jeep, open the hood, and let it run to the point where the temperature gauge on your dashboard creeps past 210.
2. Once it goes past 210, go over to the engine and see if the radiator fan kicked on. (the radiator fan is right behind the grill, circular with big plastic blades) If yes, then the relay switch is working. If no, then you probably need to replace the relay switch or the radiator fan motor is bad. But more than likely, it's the notorious relay switch.
3. Turn off the Jeep asap to avoid damaging the engine.

You can purchase a 'radiator fan relay switch' from most Jeep dealerships if they have a service dept. It should be around $75.
(I saved over $700 by not taking my Jeep to an auto shop to fix this) To change out the relay switch, you need to take off the passenger side front headlight. There's a black plastic guard behind the headlight and the relay switch is located under/behind that guard. If your Jeep ever experienced this problem before, you may see a cut-out where someone replaced this part before. If there's no cut-out, you can check out this link to see a picture of where to cut.
http://rigs.corequipment.com/cebby_WJsite/cooling.htm#relay

Once you switch out the part, you should be golden.

Is the fan coming on? If not, possible lower radiator fan switch/sensor? No leaks... So overflow tanks level stays stable? How do you know it is overheating? Elevated temp guage? Engine smells overheated? Both? We need more info.

It is common for the fan to run momentarily when motor is started. After that the fan should only come on when the engine reaches a certain temperature. If the fans are not running when the engine is overheating, then it is usually the fan relay switch. Your local auto parts store should help you to locate the relay switch, and they are only a few dollars to replace. And can easily be done in 5 minutes or less.
To test the relay first, with the key in the on position, use an electrical tester to find the "hot" wire going to the relay and using a small piece of wire, connect that "hot" wire to one of the other connectors on the relay. If the fan comes on when you do this, you know that the relay switch is indeed defective.

Check for the thermostat to be defective in not recognising the temperature to switch on the fan. alternatively check the fan, the fan relay for the action. If not the relay is not switched on by the thermostat.

I would be a bit leary of hard wiring the fan. That may cause some other problems, such as the motor not getting warm enough in the winter time. I would get another opinion on the price they are giving you. I can see needing to replace the relay, but what is wrong with the wiring, unless the wiring is burnt up, you should be able to just replace the relay.

There are three cooling fan relays in the fuse block under the hood.




The fan relays above are numbered 37,39 and 40

Relay 37 is RH fan
Relays 39 and 40 are LH fan.


You can check if your fans are working by switching on the air con.
Are you having overheating problems?

Regards.

if you are losing coolant is it a bad radiator or just overheating or is it escaping into the engine pull the dipstick and look for water in the oil you will see water bubbles in it however the relay could have a short in the wiring at some point check with a test light for power rusty connections well ?