Newbie here on the forum. Typical 2003 GS300 servo issue. Replaced them (hot/cold both sides and selector on PS). No heat on either side.

Flushed radiator (looked bad-rusty water look) w Prestone 10 min flush and then have driven the car all week with the 2nd flush. Will flush and refil w antifreeze tomorrow. But after driving all week, still no heat either side. So it looks like I need to flush the heater core.

Any tips on unclogging the heater core?

 

U can do a quick check by feeling the in and out heater hoses going thru the passenger side of the firewall. When the car is warmed up, just cautiously feel the heater hoses, they both should be warm, if neither or only 1 is, then you have a plugged heater core. Sometimes u can flush the cooling system with a quality flush. But usually if it’s blocked flushing won’t work because the coolant and cleaner aren’t flowing over the restriction fast enough to remove it. Sometimes u can disconnect the heater hoses and then use a high pressure water like from a garden hose, or if you really don’t want to pull the to change it, u could use a higher pressure source like what is used at the car wash. But I would avoid that option. Usually a garden hose being alternated from one side to the other can dislodge the obstruction, these are both risky. Usually an obstruction has to do with corrosion building up and that usually means a weak surface area that’s going to give out if it’s put under to much pressure. If you can’t get it flowing, the next option is to pull the dash and replace it. I would go ahead and do the evaporator while I was in There. They go out fairly regularly and removing the dash is a major undertaking u only want to do once in a car’s life. There is a sticky thread in the FAQ that has a full write up on how to remove the dash. I would try to feverything else before going with that option.

 

Thanks! If I can’t break it loose, I’ll have a shop w a power flush system try it.

 

I had a shop flush the radiator. All looks good now. The D/S servo is working. When I increase the D/S temp on the automatic Climate Control system, the servo arm moves and then moves again when I lower the temp setting.

just to be cautious, I replaced the D/S servo with a new one. Same movements when temp setting is set up/down.

However, no heat on the D/S. Lots of hot air on the P/S. The D/S left side vent is very cold. The center vent is not as cold on the D/S, but the P/S center vent is plenty hot, as is the P/S right vent.

There must be something simple I am missing. Any suggestions?

 

One issue that I ran into and found is pretty common when u have all 3 servos removed from the passenger side, the wire harness plugs are all the same and it’s actually pretty easy to insert the plugs into the wrong servos. Also did u clean out the temp sensor in the dash below the ignition? You made the sure your coolant is full and u aren’t loosing any? Another possibility would be the climate controller, the wiring or the hvac amplifier? Have u checked for a diagnostic code in the climate controller?

 

Hi,

plugs all correct (verified). I did get 3 codes. 21 (I was in my garage, so I dismissed that one, 24 and 46 when I ran the diagnostic test w the controller. The servos all worked correctly when I did the 2nd step of that diagnostic test. Air blows out of the D/S lower vent below the steering wheel (lower kick panel removed so i only was checking the main duct). Cannot get that air to go hot. But the D/S servo diligently raises and lowers the swing arm as I move the temp setting up and down via the button on the climate system. Just no hot air.

I just ordered a Lisle coolant filler and I am going to drain the engine coolant again. I had it power flushed by a shop last week. Maybe another couple of flushes will work on the heater core if that is the problem. I don’t think it is, but it’s just me guessing now.

 

Might be worth paying for access to the online repair data so u can skip the guessing and see what the most likely causes would be and the proven repairs. The Climate Control in these cars isn’t the most intuitive system I have seen. You have covered the obvious stuff, for $15 you should able to pin point the problem with ease. All the mechanical/electrical aspects of the system make it tough to diagnose without experience or the technical info found in a repair manual